QUIC-LB: Generating Routable QUIC Connection IDs
draft-ietf-quic-load-balancers-06

Document Type Active Internet-Draft (quic WG)
Authors Martin Duke  , Nick Banks 
Last updated 2021-02-04
Replaces draft-duke-quic-load-balancers
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QUIC                                                             M. Duke
Internet-Draft                                         F5 Networks, Inc.
Intended status: Standards Track                                N. Banks
Expires: 8 August 2021                                         Microsoft
                                                         4 February 2021

            QUIC-LB: Generating Routable QUIC Connection IDs
                   draft-ietf-quic-load-balancers-06

Abstract

   The QUIC protocol design is resistant to transparent packet
   inspection, injection, and modification by intermediaries.  However,
   the server can explicitly cooperate with network services by agreeing
   to certain conventions and/or sharing state with those services.
   This specification provides a standardized means of solving three
   problems: (1) maintaining routability to servers via a low-state load
   balancer even when the connection IDs in use change; (2) explicit
   encoding of the connection ID length in all packets to assist
   hardware accelerators; and (3) injection of QUIC Retry packets by an
   anti-Denial-of-Service agent on behalf of the server.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 8 August 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.

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   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   5
     1.2.  Notation  . . . . . . . . . . . . . . . . . . . . . . . .   5
   2.  Protocol Objectives . . . . . . . . . . . . . . . . . . . . .   6
     2.1.  Simplicity  . . . . . . . . . . . . . . . . . . . . . . .   6
     2.2.  Security  . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  First CID octet . . . . . . . . . . . . . . . . . . . . . . .   7
     3.1.  Config Rotation . . . . . . . . . . . . . . . . . . . . .   7
     3.2.  Configuration Failover  . . . . . . . . . . . . . . . . .   8
     3.3.  Length Self-Description . . . . . . . . . . . . . . . . .   8
     3.4.  Format  . . . . . . . . . . . . . . . . . . . . . . . . .   8
   4.  Load Balancing Preliminaries  . . . . . . . . . . . . . . . .   9
     4.1.  Non-Compliant Connection IDs  . . . . . . . . . . . . . .   9
     4.2.  Arbitrary Algorithms  . . . . . . . . . . . . . . . . . .  10
     4.3.  Server ID Allocation  . . . . . . . . . . . . . . . . . .  11
       4.3.1.  Static Allocation . . . . . . . . . . . . . . . . . .  11
       4.3.2.  Dynamic Allocation  . . . . . . . . . . . . . . . . .  12
   5.  Routing Algorithms  . . . . . . . . . . . . . . . . . . . . .  14
     5.1.  Plaintext CID Algorithm . . . . . . . . . . . . . . . . .  14
       5.1.1.  Configuration Agent Actions . . . . . . . . . . . . .  14
       5.1.2.  Load Balancer Actions . . . . . . . . . . . . . . . .  14
       5.1.3.  Server Actions  . . . . . . . . . . . . . . . . . . .  14
     5.2.  Stream Cipher CID Algorithm . . . . . . . . . . . . . . .  15
       5.2.1.  Configuration Agent Actions . . . . . . . . . . . . .  15
       5.2.2.  Load Balancer Actions . . . . . . . . . . . . . . . .  15
       5.2.3.  Server Actions  . . . . . . . . . . . . . . . . . . .  17
     5.3.  Block Cipher CID Algorithm  . . . . . . . . . . . . . . .  17
       5.3.1.  Configuration Agent Actions . . . . . . . . . . . . .  17
       5.3.2.  Load Balancer Actions . . . . . . . . . . . . . . . .  17
       5.3.3.  Server Actions  . . . . . . . . . . . . . . . . . . .  18
   6.  ICMP Processing . . . . . . . . . . . . . . . . . . . . . . .  18
   7.  Retry Service . . . . . . . . . . . . . . . . . . . . . . . .  18
     7.1.  Common Requirements . . . . . . . . . . . . . . . . . . .  19
     7.2.  No-Shared-State Retry Service . . . . . . . . . . . . . .  20
       7.2.1.  Configuration Agent Actions . . . . . . . . . . . . .  20
       7.2.2.  Service Requirements  . . . . . . . . . . . . . . . .  20
       7.2.3.  Server Requirements . . . . . . . . . . . . . . . . .  22
     7.3.  Shared-State Retry Service  . . . . . . . . . . . . . . .  22
       7.3.1.  Token Protection with AEAD  . . . . . . . . . . . . .  24
       7.3.2.  Configuration Agent Actions . . . . . . . . . . . . .  25

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       7.3.3.  Service Requirements  . . . . . . . . . . . . . . . .  25
       7.3.4.  Server Requirements . . . . . . . . . . . . . . . . .  26
   8.  Configuration Requirements  . . . . . . . . . . . . . . . . .  27
   9.  Additional Use Cases  . . . . . . . . . . . . . . . . . . . .  28
     9.1.  Load balancer chains  . . . . . . . . . . . . . . . . . .  28
     9.2.  Moving connections between servers  . . . . . . . . . . .  28
   10. Version Invariance of QUIC-LB . . . . . . . . . . . . . . . .  28
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  30
     11.1.  Attackers not between the load balancer and server . . .  30
     11.2.  Attackers between the load balancer and server . . . . .  30
     11.3.  Multiple Configuration IDs . . . . . . . . . . . . . . .  31
     11.4.  Limited configuration scope  . . . . . . . . . . . . . .  31
     11.5.  Stateless Reset Oracle . . . . . . . . . . . . . . . . .  31
     11.6.  Connection ID Entropy  . . . . . . . . . . . . . . . . .  31
     11.7.  Shared-State Retry Keys  . . . . . . . . . . . . . . . .  32
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  33
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  33
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  33
     13.2.  Informative References . . . . . . . . . . . . . . . . .  33
   Appendix A.  QUIC-LB YANG Model . . . . . . . . . . . . . . . . .  34
     A.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .  39
   Appendix B.  Load Balancer Test Vectors . . . . . . . . . . . . .  39
     B.1.  Plaintext Connection ID Algorithm . . . . . . . . . . . .  40
     B.2.  Stream Cipher Connection ID Algorithm . . . . . . . . . .  41
     B.3.  Block Cipher Connection ID Algorithm  . . . . . . . . . .  42
   Appendix C.  Acknowledgments  . . . . . . . . . . . . . . . . . .  44
   Appendix D.  Change Log . . . . . . . . . . . . . . . . . . . . .  44
     D.1.  since draft-ietf-quic-load-balancers-05 . . . . . . . . .  44
     D.2.  since draft-ietf-quic-load-balancers-04 . . . . . . . . .  44
     D.3.  since-draft-ietf-quic-load-balancers-03 . . . . . . . . .  44
     D.4.  since-draft-ietf-quic-load-balancers-02 . . . . . . . . .  45
     D.5.  since-draft-ietf-quic-load-balancers-01 . . . . . . . . .  45
     D.6.  since-draft-ietf-quic-load-balancers-00 . . . . . . . . .  45
     D.7.  Since draft-duke-quic-load-balancers-06 . . . . . . . . .  45
     D.8.  Since draft-duke-quic-load-balancers-05 . . . . . . . . .  45
     D.9.  Since draft-duke-quic-load-balancers-04 . . . . . . . . .  46
     D.10. Since draft-duke-quic-load-balancers-03 . . . . . . . . .  46
     D.11. Since draft-duke-quic-load-balancers-02 . . . . . . . . .  46
     D.12. Since draft-duke-quic-load-balancers-01 . . . . . . . . .  46
     D.13. Since draft-duke-quic-load-balancers-00 . . . . . . . . .  46
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  46

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1.  Introduction

   QUIC packets [QUIC-TRANSPORT] usually contain a connection ID to
   allow endpoints to associate packets with different address/ port
   4-tuples to the same connection context.  This feature makes
   connections robust in the event of NAT rebinding.  QUIC endpoints
   usually designate the connection ID which peers use to address
   packets.  Server-generated connection IDs create a potential need for
   out-of-band communication to support QUIC.

   QUIC allows servers (or load balancers) to designate an initial
   connection ID to encode useful routing information for load
   balancers.  It also encourages servers, in packets protected by
   cryptography, to provide additional connection IDs to the client.
   This allows clients that know they are going to change IP address or
   port to use a separate connection ID on the new path, thus reducing
   linkability as clients move through the world.

   There is a tension between the requirements to provide routing
   information and mitigate linkability.  Ultimately, because new
   connection IDs are in protected packets, they must be generated at
   the server if the load balancer does not have access to the
   connection keys.  However, it is the load balancer that has the
   context necessary to generate a connection ID that encodes useful
   routing information.  In the absence of any shared state between load
   balancer and server, the load balancer must maintain a relatively
   expensive table of server-generated connection IDs, and will not
   route packets correctly if they use a connection ID that was
   originally communicated in a protected NEW_CONNECTION_ID frame.

   This specification provides common algorithms for encoding the server
   mapping in a connection ID given some shared parameters.  The mapping
   is generally only discoverable by observers that have the parameters,
   preserving unlinkability as much as possible.

   Aside from load balancing, a QUIC server may also desire to offload
   other protocol functions to trusted intermediaries.  These
   intermediaries might include hardware assist on the server host
   itself, without access to fully decrypted QUIC packets.  For example,
   this document specifies a means of offloading stateless retry to
   counter Denial of Service attacks.  It also proposes a system for
   self-encoding connection ID length in all packets, so that crypto
   offload can consistently look up key information.

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   While this document describes a small set of configuration parameters
   to make the server mapping intelligible, the means of distributing
   these parameters between load balancers, servers, and other trusted
   intermediaries is out of its scope.  There are numerous well-known
   infrastructures for distribution of configuration.

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS.  Lower case uses of these words are not to be
   interpreted as carrying significance described in RFC 2119.

   In this document, "client" and "server" refer to the endpoints of a
   QUIC connection unless otherwise indicated.  A "load balancer" is an
   intermediary for that connection that does not possess QUIC
   connection keys, but it may rewrite IP addresses or conduct other IP
   or UDP processing.  A "configuration agent" is the entity that
   determines the QUIC-LB configuration parameters for the network and
   leverages some system to distribute that configuration.

   Note that stateful load balancers that act as proxies, by terminating
   a QUIC connection with the client and then retrieving data from the
   server using QUIC or another protocol, are treated as a server with
   respect to this specification.

   For brevity, "Connection ID" will often be abbreviated as "CID".

1.2.  Notation

   All wire formats will be depicted using the notation defined in
   Section 1.3 of [QUIC-TRANSPORT].  There is one addition: the function
   len() refers to the length of a field which can serve as a limit on a
   different field, so that the lengths of two fields can be concisely
   defined as limited to a sum, for example:

   x(A..B) y(C..B-len(x))

   indicates that x can be of any length between A and B, and y can be
   of any length between C and B provided that (len(x) + len(y)) does
   not exceed B.

   The example below illustrates the basic framework:

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Example Structure {
  One-bit Field (1),
  7-bit Field with Fixed Value (7) = 61,
  Field with Variable-Length Integer (i),
  Arbitrary-Length Field (..),
  Variable-Length Field (8..24),
  Variable-Length Field with Dynamic Limit (8..24-len(Variable-Length Field)),
  Field With Minimum Length (16..),
  Field With Maximum Length (..128),
  [Optional Field (64)],
  Repeated Field (8) ...,
}

                       Figure 1: Example Format

2.  Protocol Objectives

2.1.  Simplicity

   QUIC is intended to provide unlinkability across connection
   migration, but servers are not required to provide additional
   connection IDs that effectively prevent linkability.  If the
   coordination scheme is too difficult to implement, servers behind
   load balancers using connection IDs for routing will use trivially
   linkable connection IDs.  Clients will therefore be forced to choose
   between terminating the connection during migration or remaining
   linkable, subverting a design objective of QUIC.

   The solution should be both simple to implement and require little
   additional infrastructure for cryptographic keys, etc.

2.2.  Security

   In the limit where there are very few connections to a pool of
   servers, no scheme can prevent the linking of two connection IDs with
   high probability.  In the opposite limit, where all servers have many
   connections that start and end frequently, it will be difficult to
   associate two connection IDs even if they are known to map to the
   same server.

   QUIC-LB is relevant in the region between these extremes: when the
   information that two connection IDs map to the same server is helpful
   to linking two connection IDs.  Obviously, any scheme that
   transparently communicates this mapping to outside observers
   compromises QUIC's defenses against linkability.

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   Though not an explicit goal of the QUIC-LB design, concealing the
   server mapping also complicates attempts to focus attacks on a
   specific server in the pool.

3.  First CID octet

   The first octet of a Connection ID is reserved for two special
   purposes, one mandatory (config rotation) and one optional (length
   self-description).

   Subsequent sections of this document refer to the contents of this
   octet as the "first octet."

3.1.  Config Rotation

   The first two bits of any connection ID MUST encode an identifier for
   the configuration that the connection ID uses.  This enables
   incremental deployment of new QUIC-LB settings (e.g., keys).

   When new configuration is distributed to servers, there will be a
   transition period when connection IDs reflecting old and new
   configuration coexist in the network.  The rotation bits allow load
   balancers to apply the correct routing algorithm and parameters to
   incoming packets.

   Configuration Agents SHOULD deliver new configurations to load
   balancers before doing so to servers, so that load balancers are
   ready to process CIDs using the new parameters when they arrive.

   A Configuration Agent SHOULD NOT use a codepoint to represent a new
   configuration until it takes precautions to make sure that all
   connections using CIDs with an old configuration at that codepoint
   have closed or transitioned.

   Servers MUST NOT generate new connection IDs using an old
   configuration after receiving a new one from the configuration agent.
   Servers MUST send NEW_CONNECTION_ID frames that provide CIDs using
   the new configuration, and retire CIDs using the old configuration
   using the "Retire Prior To" field of that frame.

   It also possible to use these bits for more long-lived distinction of
   different configurations, but this has privacy implications (see
   Section 11.3).

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3.2.  Configuration Failover

   If a server has not received a valid QUIC-LB configuration, and
   believes that low-state, Connection-ID aware load balancers are in
   the path, it SHOULD generate connection IDs with the config rotation
   bits set to '11' and SHOULD use the "disable_active_migration"
   transport parameter in all new QUIC connections.  It SHOULD NOT send
   NEW_CONNECTION_ID frames with new values.

   A load balancer that sees a connection ID with config rotation bits
   set to '11' MUST revert to 5-tuple routing.

3.3.  Length Self-Description

   Local hardware cryptographic offload devices may accelerate QUIC
   servers by receiving keys from the QUIC implementation indexed to the
   connection ID.  However, on physical devices operating multiple QUIC
   servers, it is impractical to efficiently lookup these keys if the
   connection ID does not self-encode its own length.

   Note that this is a function of particular server devices and is
   irrelevant to load balancers.  As such, load balancers MAY omit this
   from their configuration.  However, the remaining 6 bits in the first
   octet of the Connection ID are reserved to express the length of the
   following connection ID, not including the first octet.

   A server not using this functionality SHOULD make the six bits appear
   to be random.

3.4.  Format

   First Octet {
     Config Rotation (2),
     CID Len or Random Bits (6),
   }

                        Figure 2: First Octet Format

   The first octet has the following fields:

   Config Rotation: Indicates the configuration used to interpret the
   CID.

   CID Len or Random Bits: Length Self-Description (if applicable), or
   random bits otherwise.  Encodes the length of the Connection ID
   following the First Octet.

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4.  Load Balancing Preliminaries

   In QUIC-LB, load balancers do not generate individual connection IDs
   for servers.  Instead, they communicate the parameters of an
   algorithm to generate routable connection IDs.

   The algorithms differ in the complexity of configuration at both load
   balancer and server.  Increasing complexity improves obfuscation of
   the server mapping.

   This section describes three participants: the configuration agent,
   the load balancer, and the server.  For any given QUIC-LB
   configuration that enables connection-ID-aware load balancing, there
   must be a choice of (1) routing algorithm, (2) server ID allocation
   strategy, and (3) algorithm parameters.

   Fundamentally, servers generate connection IDs that encode their
   server ID.  Load balancers decode the server ID from the CID in
   incoming packets to route to the correct server.

   There are situations where a server pool might be operating two or
   more routing algorithms or parameter sets simultaneously.  The load
   balancer uses the first two bits of the connection ID to multiplex
   incoming DCIDs over these schemes (see Section 3.1).

4.1.  Non-Compliant Connection IDs

   QUIC-LB servers will generate Connection IDs that are decodable to
   extract a server ID in accordance with a specified algorithm and
   parameters.  However, QUIC often uses client-generated Connection IDs
   prior to receiving a packet from the server.

   These client-generated CIDs might not conform to the expectations of
   the routing algorithm and therefore not be routable by the load
   balancer.  These are called "non-compliant DCIDs":

   *  The config rotation bits (Section 3.1) may not correspond to an
      active configuration.  Note: a packet with a DCID that indicates
      5-tuple routing (see Section 3.2) is always compliant.

   *  The DCID might not be long enough for the decoder to process.

   *  The extracted server mapping might not correspond to an active
      server.

   All other DCIDs are compliant.

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   Load balancers MUST forward packets with compliant DCIDs to a server
   in accordance with the chosen routing algorithm.

   Load balancers SHOULD drop packets with non-compliant DCIDs in a
   short header.

   The routing of long headers with non-compliant DCIDs depends on the
   server ID allocation strategy, described in Section 4.3.  However,
   the load balancer MUST NOT drop these packets, with one exception.

   Load balancers MAY drop packets with long headers and non-compliant
   DCIDs if and only if it knows that the encoded QUIC version does not
   allow a non- compliant DCID in a packet with that signature.  For
   example, a load balancer can safely drop a QUIC version 1 Handshake
   packet with a non-compliant DCID, as a version 1 Handshake packet
   sent to a QUIC-LB compliant server will always have a server-
   generated compliant CID.  The prohibition against dropping packets
   with long headers remains for unknown QUIC versions.

   Furthermore, while the load balancer function MUST NOT drop packets,
   the device might implement other security policies, outside the scope
   of this specification, that might force a drop.

   Servers that receive packets with noncompliant CIDs MUST use the
   available mechanisms to induce the client to use a compliant CID in
   future packets.  In QUIC version 1, this requires using a compliant
   CID in the Source CID field of server-generated long headers.

4.2.  Arbitrary Algorithms

   There are conditions described below where a load balancer routes a
   packet using an "arbitrary algorithm."  It can choose any algorithm,
   without coordination with the servers, but the algorithm SHOULD be
   deterministic over short time scales so that related packets go to
   the same server.  The design of this algorithm SHOULD consider the
   version-invariant properties of QUIC described in [QUIC-INVARIANTS]
   to maximize its robustness to future versions of QUIC.

   An arbitrary algorithmr MUST NOT make the routing behavior dependent
   on any bits in the first octet of the QUIC packet header, except the
   first bit, which indicates a long header.  All other bits are QUIC
   version-dependent and intermediaries should not base their design on
   version-specific templates.

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   For example, one arbitrary algorithm might convert a non-compliant
   DCID to an integer and divided by the number of servers, with the
   modulus used to forward the packet.  The number of servers is usually
   consistent on the time scale of a QUIC connection handshake.  Another
   might simply hash the address/port 4-tuple.  See also Section 10.

4.3.  Server ID Allocation

   For any given configuration, the configuration agent must specify if
   server IDs will be statically or dynamically allocated.  Load
   Balancer configurations with statically allocated server IDs
   explicitly include a mapping of server IDs to forwarding addresses.
   The corresponding server configurations contain one or more unique
   server IDs.

   A dynamically allocated configuration does not include any bespoke
   assignment, reducing configuration complexity.  However, it places
   limits on the maximum server ID length and requires more state at the
   load balancer.  In certain edge cases, it can force parts of the
   system to fail over to 5-tuple routing for a short time.

   In either case, the configuration agent chooses a server ID length
   for each configuration that MUST be at least one octet.  For Static
   Allocation, the maximum length depends on the algorithm.  For dynamic
   allocation, the maximum length is 7 octets.

   A QUIC-LB configuration MAY significantly over-provision the server
   ID space (i.e., provide far more codepoints than there are servers)
   to increase the probability that a randomly generated Destination
   Connection ID is non- compliant.

   Conceptually, each configuration has its own set of server ID
   allocations, though two static configurations with identical server
   ID lengths MAY use a common allocation between them.

   A server encodes one of its assigned server IDs in any CID it
   generates using the relevant configuration.

4.3.1.  Static Allocation

   In the manual allocation method, the configuration agent assigns at
   least one server ID to each server.

   When forwarding a packet with a long header and non-compliant DCID,
   load balancers MUST forward packets with long headers and non-
   compliant DCIDs using an arbitrary algorithm as specified in
   Section 4.2.

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4.3.2.  Dynamic Allocation

   In the dynamic allocation method, the load balancer assigns server
   IDs dynamically so that configuration does not require bespoke server
   ID assignment.  This also reduces linkability.  However, it requires
   state at the load balancer that roughly scales with the number of
   connections, until the server ID codespace is exhausted.

4.3.2.1.  Configuration Agent Actions

   The configuration agent does not assign server IDs, but does
   configure a server ID length and an "LB timeout".  The server ID MUST
   be at least one and no more than seven octets.

4.3.2.2.  Load Balancer Actions

   The load balancer maintains a table of all assigned server IDs and
   corresponding routing information, which is initialized empty.  These
   tables are independent for each operating configuration.

   The load balancer MUST keep track of the most recent observation of
   each server ID, in any sort of packet it forwards, in the table and
   delete the entries when the time since that observation exceeds the
   LB Timeout.

   Note that when the load balancer's table for a configuration is
   empty, all incoming DCIDs corresponding to that configuration are
   non-compliant by definition.

   The handling of a non-compliant long-header packet depends on the
   reason for non-compliance.  The load balancer MUST applyt this logic:

   *  If the config rotation bits do not match a known configuration,
      the load balancer routes the packet using an arbitrary algorithm
      (see Section 4.2).

   *  If there is a matching configuration, but the CID is not long
      enough to apply the algorithm, the load balancer skips the first
      octet of the CID and then reads a server ID from the following
      octets, up to the server ID length.  If this server ID matches a
      known server ID for that configuration, it forwards the packet
      accordingly and takes no further action.  If it does not match, it
      routes using an arbitrary algorithm and adds the new server ID to
      that server's table entry.

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   *  If the sole reason for non-compliance is that the server ID is not
      in the load balancer's table, the load balancer routes the packet
      with an arbitrary algorithm.  It adds the decoded server ID to
      table entry for the server the algorithm chooses and forwards the
      packet accordingly.

4.3.2.3.  Server actions

   Each server maintains a list of server IDs assigned to it,
   initialized empty.  For each SID, it records the last time it
   received any packet with an CID that encoded that SID.

   Upon receipt of a packet with a client-generated DCID, the server
   MUST follow these steps in order:

   *  If the config rotation bits do not correspond to a known
      configuration, do not attempt to extract a server ID.

   *  If the DCID is not long enough to decode using the configured
      algorithm, extract a number of octets equal to the server ID
      length, beginning with the second octet.  If the extracted value
      does not match a server ID in the server's list, add it to the
      list.

   *  If the DCID is long enough to decode but the server ID is not in
      the server's list, add it to the list.

   After any possible SID is extracted, the server processes the packet
   normally.

   When a server needs a new connection ID, it uses one of the server
   IDs in its list to populate the server ID field of that CID.  It
   SHOULD vary this selection to reduce linkability within a connection.

   After loading a new configuration or long periods of idleness, a
   server may not have any available SIDs.  This is because an incoming
   packet may not the config rotation bits necessary to extract a server
   ID in accordance with the algorithm above.  When required to generate
   a CID under these conditions, the server MUST generate CIDs using the
   5-tuple routing codepoint (see Section 3.2.  Note that these
   connections will not be robust to client address changes while they
   use this connection ID.  For this reason, a server SHOULD retire
   these connection IDs and replace them with routable ones once it
   receives a client-generated CID that allows it to acquire a server
   ID.  As, statistically, one in every four such CIDs can provide a
   server ID, this is typically a short interval.

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   If a server has not received a connection ID encoding a particular
   server ID within the LB timeout, it MUST retire any outstanding CIDs
   that use that server ID and cease generating any new ones.

   A server SHOULD have a mechanism to stop using some server IDs if the
   list gets large relative to its share of the codepoint space, so that
   these allocations time out and are freed for reuse by servers that
   have recently joined the pool.

5.  Routing Algorithms

   Encryption in the algorithms below uses the AES-128-ECB cipher.
   Future standards could add new algorithms that use other ciphers to
   provide cryptographic agility in accordance with [RFC7696].  QUIC-LB
   implementations SHOULD be extensible to support new algorithms.

5.1.  Plaintext CID Algorithm

   The Plaintext CID Algorithm makes no attempt to obscure the mapping
   of connections to servers, significantly increasing linkability.  The
   format is depicted in the figure below.

   Plaintext CID {
     First Octet (8),
     Server ID (8..128),
     For Server Use (8..152-len(Server ID)),
   }

                       Figure 3: Plaintext CID Format

5.1.1.  Configuration Agent Actions

   For static SID allocation, the server ID length is limited to 16
   octets.  There are no parameters specific to this algorithm.

5.1.2.  Load Balancer Actions

   On each incoming packet, the load balancer extracts consecutive
   octets, beginning with the second octet.  These bytes represent the
   server ID.

5.1.3.  Server Actions

   The server chooses how many octets to reserve for its own use, which
   MUST be at least one octet.

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   When a server needs a new connection ID, it encodes one of its
   assigned server IDs in consecutive octets beginning with the second.
   All other bits in the connection ID, except for the first octet, MAY
   be set to any other value.  These other bits SHOULD appear random to
   observers.

5.2.  Stream Cipher CID Algorithm

   The Stream Cipher CID algorithm provides cryptographic protection at
   the cost of additional per-packet processing at the load balancer to
   decrypt every incoming connection ID.  The CID format is depicted
   below.

   Stream Cipher CID {
     First Octet (8),
     Nonce (64..120),
     Encrypted Server ID (8..128-len(Nonce)),
     For Server Use (0..152-len(Nonce)-len(Encrypted Server ID)),
   }

                     Figure 4: Stream Cipher CID Format

5.2.1.  Configuration Agent Actions

   The configuration agent assigns a server ID to every server in its
   pool, and determines a server ID length (in octets) sufficiently
   large to encode all server IDs, including potential future servers.

   The configuration agent also selects a nonce length and an 16-octet
   AES-ECB key to use for connection ID decryption.  The nonce length
   MUST be at least 8 octets and no more than 16 octets.  The nonce
   length and server ID length MUST sum to 19 or fewer octets, but
   SHOULD sum to 15 or fewer to allow space for server use.

5.2.2.  Load Balancer Actions

   Upon receipt of a QUIC packet, the load balancer extracts as many of
   the earliest octets from the destination connection ID as necessary
   to match the nonce length.  The server ID immediately follows.

   The load balancer decrypts the nonce and the server ID using the
   following three pass algorithm:

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   *  Pass 1: The load balancer decrypts the server ID using 128-bit AES
      Electronic Codebook (ECB) mode, much like QUIC header protection.
      The encrypted nonce octets are zero-padded to 16 octets.  AES-ECB
      encrypts this encrypted nonce using its key to generate a mask
      which it applies to the encrypted server id.  This provides an
      intermediate value of the server ID, referred to as server-id
      intermediate.

   server_id_intermediate = encrypted_server_id ^ AES-ECB(key, padded-
   encrypted-nonce)

   *  Pass 2: The load balancer decrypts the nonce octets using 128-bit
      AES ECB mode, using the server-id intermediate as "nonce" for this
      pass.  The server-id intermediate octets are zero-padded to 16
      octets.  AES-ECB encrypts this padded server-id intermediate using
      its key to generate a mask which it applies to the encrypted
      nonce.  This provides the decrypted nonce value.

   nonce = encrypted_nonce ^ AES-ECB(key, padded-server_id_intermediate)

   *  Pass 3: The load balancer decrypts the server ID using 128-bit AES
      ECB mode.  The nonce octets are zero-padded to 16 octets.  AES-ECB
      encrypts this nonce using its key to generate a mask which it
      applies to the intermediate server id.  This provides the
      decrypted server ID.

   server_id = server_id_intermediate ^ AES-ECB(key, padded-nonce)

   For example, if the nonce length is 10 octets and the server ID
   length is 2 octets, the connection ID can be as small as 13 octets.
   The load balancer uses the the second through eleventh octets of the
   connection ID for the nonce, zero-pads it to 16 octets, uses xors the
   result with the twelfth and thirteenth octet.  The result is padded
   with 14 octets of zeros and encrypted to obtain a mask that is xored
   with the nonce octets.  Finally, the nonce octets are padded with six
   octets of zeros, encrypted, and the first two octets xored with the
   server ID octets to obtain the actual server ID.

   This three-pass algorithm is a simplified version of the FFX
   algorithm, with the property that each encrypted nonce value depends
   on all server ID bits, and each encrypted server ID bit depends on
   all nonce bits and all server ID bits.  This mitigates attacks
   against stream ciphers in which attackers simply flip encrypted
   server-ID bits.

   The output of the decryption is the server ID that the load balancer
   uses for routing.

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5.2.3.  Server Actions

   When generating a routable connection ID, the server writes arbitrary
   bits into its nonce octets, and its provided server ID into the
   server ID octets.  Servers MAY opt to have a longer connection ID
   beyond the nonce and server ID.  The additional bits MAY encode
   additional information, but SHOULD appear essentially random to
   observers.

   If the decrypted nonce bits increase monotonically, that guarantees
   that nonces are not reused between connection IDs from the same
   server.

   The server encrypts the server ID using exactly the algorithm as
   described in Section 5.2.2, performing the three passes in reverse
   order.

5.3.  Block Cipher CID Algorithm

   The Block Cipher CID Algorithm, by using a full 16 octets of
   plaintext and a 128-bit cipher, provides higher cryptographic
   protection and detection of non-compliant connection IDs.  However,
   it also requires connection IDs of at least 17 octets, increasing
   overhead of client-to-server packets.

   Block Cipher CID {
     First Octet (8),
     Encrypted Server ID (8..128),
     Encrypted Bits for Server Use (128-len(Encrypted Server ID)),
     Unencrypted Bits for Server Use (0..24),
   }

                     Figure 5: Block Cipher CID Format

5.3.1.  Configuration Agent Actions

   If server IDs are statically allocated, the server ID length MUST be
   no more than 12 octets, to provide servers adequate entropy to
   generate unique CIDs.

   The configuration agent also selects an 16-octet AES-ECB key to use
   for connection ID decryption.

5.3.2.  Load Balancer Actions

   Upon receipt of a QUIC packet, the load balancer reads the first
   octet to obtain the config rotation bits.  It then decrypts the
   subsequent 16 octets using AES-ECB decryption and the chosen key.

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   The decrypted plaintext contains the server id and opaque server data
   in that order.  The load balancer uses the server ID octets for
   routing.

5.3.3.  Server Actions

   When generating a routable connection ID, the server MUST choose a
   connection ID length between 17 and 20 octets.  The server writes its
   server ID into the server ID octets and arbitrary bits into the
   remaining bits.  These arbitrary bits MAY encode additional
   information, and MUST differ between connection IDs.  Bits in the
   eighteenth, nineteenth, and twentieth octets SHOULD appear
   essentially random to observers.  The first octet is reserved as
   described in Section 3.

   The server then encrypts the second through seventeenth octets using
   the 128-bit AES-ECB cipher.

6.  ICMP Processing

   For protocols where 4-tuple load balancing is sufficient, it is
   straightforward to deliver ICMP packets from the network to the
   correct server, by reading the echoed IP and transport-layer headers
   to obtain the 4-tuple.  When routing is based on connection ID,
   further measures are required, as most QUIC packets that trigger ICMP
   responses will only contain a client-generated connection ID that
   contains no routing information.

   To solve this problem, load balancers MAY maintain a mapping of
   Client IP and port to server ID based on recently observed packets.

   Alternatively, servers MAY implement the technique described in
   Section 14.4.1 of [QUIC-TRANSPORT] to increase the likelihood a
   Source Connection ID is included in ICMP responses to Path Maximum
   Transmission Unit (PMTU) probes.  Load balancers MAY parse the echoed
   packet to extract the Source Connection ID, if it contains a QUIC
   long header, and extract the Server ID as if it were in a Destination
   CID.

7.  Retry Service

   When a server is under load, QUICv1 allows it to defer storage of
   connection state until the client proves it can receive packets at
   its advertised IP address.  Through the use of a Retry packet, a
   token in subsequent client Initial packets, and transport parameters,
   servers verify address ownership and clients verify that there is no
   on-path attacker generating Retry packets.

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   A "Retry Service" detects potential Denial of Service attacks and
   handles sending of Retry packets on behalf of the server.  As it is,
   by definition, literally an on-path entity, the service must
   communicate some of the original connection IDs back to the server so
   that it can pass client verification.  It also must either verify the
   address itself (with the server trusting this verification) or make
   sure there is common context for the server to verify the address
   using a service-generated token.

   There are two different mechanisms to allow offload of DoS mitigation
   to a trusted network service.  One requires no shared state; the
   server need only be configured to trust a retry service, though this
   imposes other operational constraints.  The other requires a shared
   key, but has no such constraints.

   Retry services MUST forward all QUIC packets that are not of type
   Initial or 0-RTT.  Other packet types might involve changed IP
   addresses or connection IDs, so it is not practical for Retry
   Services to identify such packets as valid or invalid.

7.1.  Common Requirements

   Regardless of mechanism, a retry service has an active mode, where it
   is generating Retry packets, and an inactive mode, where it is not,
   based on its assessment of server load and the likelihood an attack
   is underway.  The choice of mode MAY be made on a per-packet or per-
   connection basis, through a stochastic process or based on client
   address.

   A configuration agent MUST distribute a list of QUIC versions the
   Retry Service supports.  It MAY also distribute either an "Allow-
   List" or a "Deny-List" of other QUIC versions.  It MUST NOT
   distribute both an Allow-List and a Deny-List.

   The Allow-List or Deny-List MUST NOT include any versions included
   for Retry Service Support.

   The Configuration Agent MUST provide a means for the entity that
   controls the Retry Service to report its supported version(s) to the
   configuration Agent.  If the entity has not reported this
   information, it MUST NOT activate the Retry Service and the
   configuration agent MUST NOT distribute configuration that activates
   it.

   The configuration agent MAY delete versions from the final supported
   version list if policy does not require the Retry Service to operate
   on those versions.

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   The configuration Agent MUST provide a means for the entities that
   control servers behind the Retry Service to report either an Allow-
   List or a Deny-List.

   If all entities supply Allow-Lists, the consolidated list MUST be the
   union of these sets.  If all entities supply Deny-Lists, the
   consolidated list MUST be the intersection of these sets.

   If entities provide a mixture of Allow-Lists and Deny-Lists, the
   consolidated list MUST be a Deny-List that is the intersection of all
   provided Deny-Lists and the inverses of all Allow-Lists.

   If no entities that control servers have reported Allow-Lists or
   Deny-Lists, the default is a Deny-List with the null set (i.e., all
   unsupported versions will be admitted).  This preserves the future
   extensibilty of QUIC.

   A retry service MUST forward all packets for a QUIC version it does
   not support that are not on a Deny-List or absent from an Allow-List.
   Note that if servers support versions the retry service does not,
   this may increase load on the servers.

   Note that future versions of QUIC might not have Retry packets,
   require different information in Retry, or use different packet type
   indicators.

7.2.  No-Shared-State Retry Service

   The no-shared-state retry service requires no coordination, except
   that the server must be configured to accept this service and know
   which QUIC versions the retry service supports.  The scheme uses the
   first bit of the token to distinguish between tokens from Retry
   packets (codepoint '0') and tokens from NEW_TOKEN frames (codepoint
   '1').

7.2.1.  Configuration Agent Actions

   See Section 7.1.

7.2.2.  Service Requirements

   A no-shared-state retry service MUST be present on all paths from
   potential clients to the server.  These paths MUST fail to pass QUIC
   traffic should the service fail for any reason.  That is, if the
   service is not operational, the server MUST NOT be exposed to client
   traffic.  Otherwise, servers that have already disabled their Retry
   capability would be vulnerable to attack.

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   The path between service and server MUST be free of any potential
   attackers.  Note that this and other requirements above severely
   restrict the operational conditions in which a no-shared-state retry
   service can safely operate.

   Retry tokens generated by the service MUST have the format below.

   Non-Shared-State Retry Service Token {
     Token Type (1) = 0,
     ODCIL (7) = 8..20,
     RSCIL (8) = 0..20,
     Original Destination Connection ID (64..160),
     Retry Source Connection ID (0..160),
     Opaque Data (..),
   }

         Figure 6: Format of non-shared-state retry service tokens

   The first bit of retry tokens generated by the service MUST be zero.
   The token has the following additional fields:

   ODCIL: The length of the original destination connection ID from the
   triggering Initial packet.  This is in cleartext to be readable for
   the server, but authenticated later in the token.  The Retry Service
   SHOULD reject any token in which the value is less than 8.

   RSCIL: The retry source connection ID length.

   Original Destination Connection ID: This also in cleartext and
   authenticated later.

   Retry Source Connection ID: This also in cleartext and authenticated
   later.

   Opaque Data: This data MUST contain encrypted information that allows
   the retry service to validate the client's IP address, in accordance
   with the QUIC specification.  It MUST also provide a
   cryptographically secure means to validate the integrity of the
   entire token.

   Upon receipt of an Initial packet with a token that begins with '0',
   the retry service MUST validate the token in accordance with the QUIC
   specification.

   In active mode, the service MUST issue Retry packets for all Client
   initial packets that contain no token, or a token that has the first
   bit set to '1'.  It MUST NOT forward the packet to the server.  The
   service MUST validate all tokens with the first bit set to '0'.  If

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   successful, the service MUST forward the packet with the token
   intact.  If unsuccessful, it MUST drop the packet.  The Retry Service
   MAY send an Initial Packet containing a CONNECTION_CLOSE frame with
   the INVALID_TOKEN error code when dropping the packet.

   Note that this scheme has a performance drawback.  When the retry
   service is in active mode, clients with a token from a NEW_TOKEN
   frame will suffer a 1-RTT penalty even though its token provides
   proof of address.

   In inactive mode, the service MUST forward all packets that have no
   token or a token with the first bit set to '1'.  It MUST validate all
   tokens with the first bit set to '0'.  If successful, the service
   MUST forward the packet with the token intact.  If unsuccessful, it
   MUST either drop the packet or forward it with the token removed.
   The latter requires decryption and re-encryption of the entire
   Initial packet to avoid authentication failure.  Forwarding the
   packet causes the server to respond without the
   original_destination_connection_id transport parameter, which
   preserves the normal QUIC signal to the client that there is an on-
   path attacker.

7.2.3.  Server Requirements

   A server behind a non-shared-state retry service MUST NOT send Retry
   packets for a QUIC version the retry service understands.  It MAY
   send Retry for QUIC versions the Retry Service does not understand.

   Tokens sent in NEW_TOKEN frames MUST have the first bit set to '1'.

   If a server receives an Initial Packet with the first bit set to '1',
   it could be from a server-generated NEW_TOKEN frame and should be
   processed in accordance with the QUIC specification.  If a server
   receives an Initial Packet with the first bit to '0', it is a Retry
   token and the server MUST NOT attempt to validate it.  Instead, it
   MUST assume the address is validated and MUST extract the Original
   Destination Connection ID and Retry Source Connection ID, assuming
   the format described in Section 7.2.2.

7.3.  Shared-State Retry Service

   A shared-state retry service uses a shared key, so that the server
   can decode the service's retry tokens.  It does not require that all
   traffic pass through the Retry service, so servers MAY send Retry
   packets in response to Initial packets that don't include a valid
   token.

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   Both server and service must have access to Universal time, though
   tight synchronization is unnecessary.

   The tokens are protected using AES128-GCM AEAD, as explained in
   Section 7.3.1.  All tokens, generated by either the server or retry
   service, MUST use the following format, which includes:

   *  A 96 bit unique token number transmitted in clear text, but
      protected as part of the AEAD associated data.

   *  An 8 bit token key identifier.

   *  A token body, encoding the Original Destination Connection ID, the
      Retry Source Connection ID, and the Timestamp, optionally followed
      by server specific Opaque Data.

   The token protection uses an 128 bit representation of the source IP
   address from the triggering Initial packet.  The client IP address is
   16 octets.  If an IPv4 address, the last 12 octets are zeroes.

   If there is a Network Address Translator (NAT) in the server
   infrastructure that changes the client IP, the Retry Service MUST
   either be positioned behind the NAT, or the NAT must have the token
   key to rewrite the Retry token accordingly.  Note also that a host
   that obtains a token through a NAT and then attempts to connect over
   a path that does not have an identically configured NAT will fail
   address validation.

   The 96 bit unique token number is set to a random value using a
   cryptography- grade random number generator.

   The token key identifier and the corresponding AEAD key and AEAD IV
   are provisioned by the configuration agent.

   The token body is encoded as follows:

   Shared-State Retry Service Token Body {
      ODCIL (8) = 0..20,
      RSCIL (8) = 0..20,
      [Port (16)],
      Original Destination Connection ID (0..160),
      Retry Source Connection ID (0..160),
      Timestamp (64),
      Opaque Data (..),
   }

            Figure 7: Body of shared-state retry service tokens

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   The token body has the following fields:

   ODCIL: The original destination connection ID length.  Tokens in
   NEW_TOKEN frames MUST set this field to zero.

   RSCIL: The retry source connection ID length.  Tokens in NEW_TOKEN
   frames MUST set this field to zero.

   Port: The Source Port of the UDP datagram that triggered the Retry
   packet.  This field MUST be present if and only if the ODCIL is
   greater than zero.  This field is therefore always absent in tokens
   in NEW_TOKEN frames.

   Original Destination Connection ID: The server or Retry Service
   copies this from the field in the client Initial packet.

   Retry Source Connection ID: The server or Retry service copies this
   from the Source Connection ID of the Retry packet.

   Timestamp: The Timestamp is a 64-bit integer, in network order, that
   expresses the expiration time of the token as a number of seconds in
   POSIX time (see Sec. 4.16 of [TIME_T]).

   Opaque Data: The server may use this field to encode additional
   information, such as congestion window, RTT, or MTU.  The Retry
   Service MUST have zero-length opaque data.

   Some implementations of QUIC encode in the token the Initial Packet
   Number used by the client, in order to verify that the client sends
   the retried Initial with a PN larger that the triggering Initial.
   Such implementations will encode the Initial Packet Number as part of
   the opaque data.  As tokens may be generated by the Service, servers
   MUST NOT reject tokens because they lack opaque data and therefore
   the packet number.

7.3.1.  Token Protection with AEAD

   On the wire, the token is presented as:

   Shared-State Retry Service Token {
     Unique Token Number (96),
     Key Sequence (8),
     Encrypted Shared-State Retry Service Token Body (80..),
     AEAD Checksum (length depends on encryption algorithm),
   }

         Figure 8: Wire image of shared-state retry service tokens

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   The tokens are protected using AES128-GCM as follows:

   *  The token key and IV are retrieved using the Key Sequence.

   *  The nonce, N, is formed by combining the IV with the 96 bit unique
      token number.  The 96 bits of the unique token number are left-
      padded with zeros to the size of the IV.  The exclusive OR of the
      padded unique token number and the IV forms the AEAD nonce.

   *  The associated data is a formatted as a pseudo header by combining
      the cleartext part of the token with the IP address of the client.

   Shared-State Retry Service Token Pseudoheader {
     IP Address (128),
     Unique Token Number (96),
     Key Sequence (8),
   }

        Figure 9: Psuedoheader for shared-state retry service tokens

   *  The input plaintext for the AEAD is the token body.  The output
      ciphertext of the AEAD is transmitted in place of the token body.

   *  The AEAD Checksum is computed as part of the AEAD encryption
      process, and is verified during decryption.

7.3.2.  Configuration Agent Actions

   The configuration agent generates and distributes a "token key", a
   "token IV", a key sequence, and the information described in
   Section 7.1.

7.3.3.  Service Requirements

   In inactive mode, the Retry service forwards all packets without
   further inspection or processing.

   Retry services MUST NOT issue Retry packets except where explicitly
   allowed below, to avoid sending a Retry packet in response to a Retry
   token.

   When in active mode, the service MUST generate Retry tokens with the
   format described above when it receives a client Initial packet with
   no token.

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   The service SHOULD decrypt incoming tokens.  The service SHOULD drop
   packets with unknown key sequence, or an AEAD checksum that does not
   match the expected value.  (By construction, the AEAD checksum will
   only match if the client IP Address also matches.)

   If the token checksum passes, and the ODCIL and RSCIL fields are both
   zero, then this is a NEW_TOKEN token generated by the server.
   Processing of NEW_TOKEN tokens is subtly different from Retry tokens,
   as described below.

   The service SHOULD drop a packet containing a token where the ODCIL
   is greater than zero and less than the minimum number of octets for a
   client-generated CID (8 in QUIC version 1).  The service also SHOULD
   drop a packet containing a token where the ODCIL is zero and RSCIL is
   nonzero.

   If the Timestamp of a token points to time in the past, the token has
   expired; however, in order to allow for clock skew, it SHOULD NOT
   consider tokens to be expired if the Timestamp encodes a few seconds
   in the past.  An active Retry service SHOULD drop packets with
   expired tokens.  If a NEW_TOKEN token, the service MUST generate a
   Retry packet in response.  It MUST NOT generate a Retry packet in
   response to an expired Retry token.

   If a Retry token, the service SHOULD drop packets where the port
   number encoded in the token does not match the source port in the
   encapsulating UDP header.

   All other packets SHOULD be forwarded to the server.

7.3.4.  Server Requirements

   When issuing Retry or NEW_TOKEN tokens, the server MUST include the
   client IP address in the authenticated data as specified in
   Section 7.3.1.  The ODCIL and RSCIL fields are zero for NEW_TOKEN
   tokens, making them easily distinguishable from Retry tokens.

   The server MUST validate all tokens that arrive in Initial packets,
   as they may have bypassed the Retry service.

   For Retry tokens that follow the format above, servers SHOULD use the
   timestamp field to apply its expiration limits for tokens.  This need
   not be precisely synchronized with the retry service.  However,
   servers MAY allow retry tokens marked as being a few seconds in the
   past, due to possible clock synchronization issues.

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   After decrypting the token, the server uses the corresponding fields
   to populate the original_destination_connection_id transport
   parameter, with a length equal to ODCIL, and the
   retry_source_connection_id transport parameter, with length equal to
   RSCIL.

   For QUIC versions the service does not support, the server MAY use
   any token format.

   As discussed in [QUIC-TRANSPORT], a server MUST NOT send a Retry
   packet in response to an Initial packet that contains a retry token.

8.  Configuration Requirements

   QUIC-LB requires common configuration to synchronize understanding of
   encodings and guarantee explicit consent of the server.

   The load balancer and server MUST agree on a routing algorithm,
   server ID allocation method, and the relevant parameters for that
   algorithm.

   All algorithms require a server ID length.  If server IDs are
   statically allocated, the load balancer MUST receive the full table
   of mappings, and each server must receive its assigned SID(s), from
   the configuration agent.

   For Stream Cipher CID Routing, the servers and load balancer also
   MUST have a common understanding of the key and nonce length.

   For Block Cipher CID Routing, the servers and load balancer also MUST
   have a common understanding of the key.

   Note that server IDs are opaque bytes, not integers, so there is no
   notion of network order or host order.

   A server configuration MUST specify if the first octet encodes the
   CID length.  Note that a load balancer does not need the CID length,
   as the required bytes are present in the QUIC packet.

   A full QUIC-LB server configuration MUST also specify the supported
   QUIC versions of any Retry Service.  If a shared-state service, the
   server also must have the token key.

   A non-shared-state Retry Service need only be configured with the
   QUIC versions it supports, and an Allow- or Deny-List.  A shared-
   state Retry Service also needs the token key, and to be aware if a
   NAT sits between it and the servers.

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   Appendix A provides a YANG Model of the a full QUIC-LB configuration.

9.  Additional Use Cases

   This section discusses considerations for some deployment scenarios
   not implied by the specification above.

9.1.  Load balancer chains

   Some network architectures may have multiple tiers of low-state load
   balancers, where a first tier of devices makes a routing decision to
   the next tier, and so on, until packets reach the server.  Although
   QUIC-LB is not explicitly designed for this use case, it is possible
   to support it.

   If each load balancer is assigned a range of server IDs that is a
   subset of the range of IDs assigned to devices that are closer to the
   client, then the first devices to process an incoming packet can
   extract the server ID and then map it to the correct forwarding
   address.  Note that this solution is extensible to arbitrarily large
   numbers of load-balancing tiers, as the maximum server ID space is
   quite large.

9.2.  Moving connections between servers

   Some deployments may transparently move a connection from one server
   to another.  The means of transferring connection state between
   servers is out of scope of this document.

   To support a handover, a server involved in the transition could
   issue CIDs that map to the new server via a NEW_CONNECTION_ID frame,
   and retire CIDs associated with the new server using the "Retire
   Prior To" field in that frame.

   Alternately, if the old server is going offline, the load balancer
   could simply map its server ID to the new server's address.

10.  Version Invariance of QUIC-LB

   Non-shared-state Retry Services are inherently dependent on the
   format (and existence) of Retry Packets in each version of QUIC, and
   so Retry Service configuration explicitly includes the supported QUIC
   versions.

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   The server ID encodings, and requirements for their handling, are
   designed to be QUIC version independent (see [QUIC-INVARIANTS]).  A
   QUIC-LB load balancer will generally not require changes as servers
   deploy new versions of QUIC.  However, there are several unlikely
   future design decisions that could impact the operation of QUIC-LB.

   The maximum Connection ID length could be below the minimum necessary
   for one or more encoding algorithms.

   Section 4.1 provides guidance about how load balancers should handle
   non-compliant DCIDs.  This guidance, and the implementation of an
   algorithm to handle these DCIDs, rests on some assumptions:

   *  Incoming short headers do not contain DCIDs that are client-
      generated.

   *  The use of client-generated incoming DCIDs does not persist beyond
      a few round trips in the connection.

   *  While the client is using DCIDs it generated, some exposed fields
      (IP address, UDP port, client-generated destination Connection ID)
      remain constant for all packets sent on the same connection.

   *  Dynamic server ID allocation is dependent on client-generated
      Destination CIDs in Initial Packets being at least 8 octets in
      length.  If they are not, the load balancer may not be able to
      extract a valid server ID to add to its table.  Configuring a
      shorter server ID length can increase robustness to a change.

   While this document does not update the commitments in
   [QUIC-INVARIANTS], the additional assumptions are minimal and
   narrowly scoped, and provide a likely set of constants that load
   balancers can use with minimal risk of version- dependence.

   If these assumptions are invalid, this specification is likely to
   lead to loss of packets that contain non-compliant DCIDs, and in
   extreme cases connection failure.

   Some load balancers might inspect elements of the Server Name
   Indication (SNI) extension in the TLS Client Hello to make a routing
   decision.  Note that the format and cryptographic protection of this
   information may change in future versions or extensions of TLS or
   QUIC, and therefore this functionality is inherently not version-
   invariant.

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11.  Security Considerations

   QUIC-LB is intended to prevent linkability.  Attacks would therefore
   attempt to subvert this purpose.

   Note that the Plaintext CID algorithm makes no attempt to obscure the
   server mapping, and therefore does not address these concerns.  It
   exists to allow consistent CID encoding for compatibility across a
   network infrastructure, which makes QUIC robust to NAT rebinding.
   Servers that are running the Plaintext CID algorithm SHOULD only use
   it to generate new CIDs for the Server Initial Packet and SHOULD NOT
   send CIDs in QUIC NEW_CONNECTION_ID frames, except that it sends one
   new Connection ID in the event of config rotation Section 3.1.  Doing
   so might falsely suggest to the client that said CIDs were generated
   in a secure fashion.

   A linkability attack would find some means of determining that two
   connection IDs route to the same server.  As described above, there
   is no scheme that strictly prevents linkability for all traffic
   patterns, and therefore efforts to frustrate any analysis of server
   ID encoding have diminishing returns.

11.1.  Attackers not between the load balancer and server

   Any attacker might open a connection to the server infrastructure and
   aggressively simulate migration to obtain a large sample of IDs that
   map to the same server.  It could then apply analytical techniques to
   try to obtain the server encoding.

   The Stream and Block Cipher CID algorithms provide robust protection
   against any sort of linkage.  The Plaintext CID algorithm makes no
   attempt to protect this encoding.

   Were this analysis to obtain the server encoding, then on-path
   observers might apply this analysis to correlating different client
   IP addresses.

11.2.  Attackers between the load balancer and server

   Attackers in this privileged position are intrinsically able to map
   two connection IDs to the same server.  The QUIC-LB algorithms do
   prevent the linkage of two connection IDs to the same individual
   connection if servers make reasonable selections when generating new
   IDs for that connection.

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11.3.  Multiple Configuration IDs

   During the period in which there are multiple deployed configuration
   IDs (see Section 3.1), there is a slight increase in linkability.
   The server space is effectively divided into segments with CIDs that
   have different config rotation bits.  Entities that manage servers
   SHOULD strive to minimize these periods by quickly deploying new
   configurations across the server pool.

11.4.  Limited configuration scope

   A simple deployment of QUIC-LB in a cloud provider might use the same
   global QUIC-LB configuration across all its load balancers that route
   to customer servers.  An attacker could then simply become a
   customer, obtain the configuration, and then extract server IDs of
   other customers' connections at will.

   To avoid this, the configuration agent SHOULD issue QUIC-LB
   configurations to mutually distrustful servers that have different
   keys for encryption algorithms.  The load balancers can distinguish
   these configurations by external IP address, or by assigning
   different values to the config rotation bits (Section 3.1).  Note
   that either solution has a privacy impact; see Section 11.3.

   These techniques are not necessary for the plaintext algorithm, as it
   does not attempt to conceal the server ID.

11.5.  Stateless Reset Oracle

   Section 21.9 of [QUIC-TRANSPORT] discusses the Stateless Reset Oracle
   attack.  For a server deployment to be vulnerable, an attacking
   client must be able to cause two packets with the same Destination
   CID to arrive at two different servers that share the same
   cryptographic context for Stateless Reset tokens.  As QUIC-LB
   requires deterministic routing of DCIDs over the life of a
   connection, it is a sufficient means of avoiding an Oracle without
   additional measures.

11.6.  Connection ID Entropy

   The Stream Cipher and Block Cipher algorithms need to generate
   different cipher text for each generated Connection ID instance to
   protect the Server ID.  To do so, at least four octets of the Block
   Cipher CID and at least eight octets of the Stream Cipher CID are
   reserved for a nonce that, if used only once, will result in unique
   cipher text for each Connection ID.

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   If servers simply increment the nonce by one with each generated
   connection ID, then it is safe to use the existing keys until any
   server's nonce counter exhausts the allocated space and rolls over to
   zero.  Whether or not it implements this method, the server MUST NOT
   reuse a nonce until it switches to a configuration with new keys.

   Configuration agents SHOULD implement an out-of-band method to
   discover when servers are in danger of exhausting their nonce space,
   and SHOULD respond by issuing a new configuration.  A server that has
   exhausted its nonces MUST either switch to a different configuration,
   or if none exists, use the 4-tuple routing config rotation codepoint.

11.7.  Shared-State Retry Keys

   The Shared-State Retry Service defined in Section 7.3 describes the
   format of retry tokens or new tokens protected and encrypted using
   AES128-GCM.  Each token includes a 96 bit randomly generated unique
   token number, and an 8 bit identifier of the AES-GCM encryption key.
   There are three important security considerations for these tokens:

   *  An attacker that obtains a copy of the encryption key will be able
      to decrypt and forge tokens.

   *  Attackers may be able to retrieve the key if they capture a
      sufficently large number of retry tokens encrypted with a given
      key.

   *  Confidentiality of the token data will fail if separate tokens
      reuse the same 96 bit unique token number and the same key.

   To protect against disclosure of keys to attackers, service and
   servers MUST ensure that the keys are stored securely.  To limit the
   consequences of potential exposures, the time to live of any given
   key should be limited.

   Section 6.6 of [QUIC-TLS] states that "Endpoints MUST count the
   number of encrypted packets for each set of keys.  If the total
   number of encrypted packets with the same key exceeds the
   confidentiality limit for the selected AEAD, the endpoint MUST stop
   using those keys."  It goes on with the specific limit: "For
   AEAD_AES_128_GCM and AEAD_AES_256_GCM, the confidentiality limit is
   2^23 encrypted packets; see Appendix B.1."  It is prudent to adopt
   the same limit here, and configure the service in such a way that no
   more than 2^23 tokens are generated with the same key.

   In order to protect against collisions, the 96 bit unique token
   numbers should be generated using a cryptographically secure
   pseudorandom number generator (CSPRNG), as specified in Appendix C.1

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   of the TLS 1.3 specification [RFC8446].  With proper random numbers,
   if fewer than 2^40 tokens are generated with a single key, the risk
   of collisions is lower than 0.001%.

12.  IANA Considerations

   There are no IANA requirements.

13.  References

13.1.  Normative References

   [QUIC-INVARIANTS]
              Thomson, M., "Version-Independent Properties of QUIC",
              Work in Progress, Internet-Draft, draft-ietf-quic-
              invariants-13, 14 January 2021, <http://www.ietf.org/
              internet-drafts/draft-ietf-quic-invariants-13.txt>.

   [QUIC-TRANSPORT]
              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", Work in Progress, Internet-Draft,
              draft-ietf-quic-transport-34, 14 January 2021,
              <http://www.ietf.org/internet-drafts/draft-ietf-quic-
              transport-34.txt>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [TIME_T]   "Open Group Standard: Vol. 1: Base Definitions, Issue 7",
              IEEE Std 1003.1 , 2018,
              <http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/
              V1_chap04.html#tag_04_16>.

13.2.  Informative References

   [QUIC-TLS] Thomson, M. and S. Turner, "Using TLS to Secure QUIC",
              Work in Progress, Internet-Draft, draft-ietf-quic-tls-34,
              14 January 2021, <http://www.ietf.org/internet-drafts/
              draft-ietf-quic-tls-34.txt>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

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   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [RFC7696]  Housley, R., "Guidelines for Cryptographic Algorithm
              Agility and Selecting Mandatory-to-Implement Algorithms",
              BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,
              <https://www.rfc-editor.org/info/rfc7696>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

Appendix A.  QUIC-LB YANG Model

   This YANG model conforms to [RFC6020] and expresses a complete QUIC-
   LB configuration.

module ietf-quic-lb {
  yang-version "1.1";
  namespace "urn:ietf:params:xml:ns:yang:ietf-quic-lb";
  prefix "quic-lb";

  import ietf-yang-types {
    prefix yang;
    reference
      "RFC 6991: Common YANG Data Types.";
  }

  import ietf-inet-types {
    prefix inet;
    reference
      "RFC 6991: Common YANG Data Types.";
  }

  organization
    "IETF QUIC Working Group";

  contact
    "WG Web:   <http://datatracker.ietf.org/wg/quic>
     WG List:  <quic@ietf.org>

     Authors: Martin Duke (martin.h.duke at gmail dot com)
              Nick Banks (nibanks at microsoft dot com)";

  description
    "This module enables the explicit cooperation of QUIC servers with

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     trusted intermediaries without breaking important protocol features.

     Copyright (c) 2021 IETF Trust and the persons identified as
     authors of the code.  All rights reserved.

     Redistribution and use in source and binary forms, with or
     without modification, is permitted pursuant to, and subject to
     the license terms contained in, the Simplified BSD License set
     forth in Section 4.c of the IETF Trust's Legal Provisions
     Relating to IETF Documents
     (https://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC XXXX
     (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
     for full legal notices.

     The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
     NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED',
     'MAY', and 'OPTIONAL' in this document are to be interpreted as
     described in BCP 14 (RFC 2119) (RFC 8174) when, and only when,
     they appear in all capitals, as shown here.";

  revision "2021-01-29" {
    description
      "Initial Version";
    reference
      "RFC XXXX, QUIC-LB: Generating Routable QUIC Connection IDs";
  }

  container quic-lb {
    presence "The container for QUIC-LB configuration.";

    description
      "QUIC-LB container.";

    typedef quic-lb-key {
      type yang:hex-string {
        length 47;
      }
      description
        "This is a 16-byte key, represented with 47 bytes";
    }

    list cid-configs {
      key "config-rotation-bits";
      description
        "List up to three load balancer configurations";

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      leaf config-rotation-bits {
        type uint8 {
          range "0..2";
        }
        mandatory true;
        description
          "Identifier for this CID configuration.";
      }

      leaf first-octet-encodes-cid-length {
        type boolean;
        default false;
        description
          "If true, the six least significant bits of the first CID
           octet encode the CID length minus one.";
      }

      leaf cid-key {
        type quic-lb-key;
        description
          "Key for encrypting the connection ID. If absent, the
           configuration uses the Plaintext algorithm.";
      }

      leaf nonce-length {
        type uint8 {
          range "8..16";
        }
        must '(../cid-key)' {
          error-message "nonce-length only valid if cid-key is set";
        }
        description
          "Length, in octets, of the nonce. If absent when cid-key is
           present, the configuration uses the Block Cipher Algorithm.
           If present along with cid-key, the configurationuses the
           Stream Cipher Algorithm.";
      }

      leaf lb-timeout {
        type uint32;
        description
          "Existence means the configuration uses dynamic Server ID allocation.
           Time (in seconds) to keep a server ID allocation if no packets with
           that server ID arrive.";
      }

      leaf server-id-length {
        type uint8 {

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          range "1..18";
        }
        must '(../lb-timeout and . <= 7) or
               (not(../lb-timeout) and
                (not(../cid-key) and . <= 16) or
                ((../nonce-length) and . <= (19 - ../nonce-length)) or
                ((../cid-key) and not(../nonce-length) and . <= 12))' {
          error-message
            "Server ID length too long for routing algorithm and server ID
             allocation method";
        }
        mandatory true;
        description
          "Length (in octets) of a server ID. Further range-limited
           by sid-allocation, cid-key, and nonce-length.";
      }

      list server-id-mappings {
        when "not(../lb-timeout)";
        key "server-id";
        description "Statically allocated Server IDs";

        leaf server-id {
          type yang:hex-string;
          must "string-length(.) = 3 * ../../server-id-length - 1";
          mandatory true;
          description
            "An allocated server ID";
        }

        leaf server-address {
          type inet:ip-address;
          mandatory true;
          description
            "Destination address corresponding to the server ID";
        }
      }
    }

    container retry-service-config {
      description
        "Configuration of Retry Service. If supported-versions is empty, there
         is no retry service. If token-keys is empty, it uses the non-shared-
         state service. If present, it uses shared-state tokens.";

      leaf-list supported-versions {
        type uint32;
        description

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          "QUIC versions that the retry service supports. If empty, there
           is no retry service.";
      }

      leaf unsupported-version-default {
        type enumeration {
          enum allow {
            description "Unsupported versions admitted by default";
          }
          enum deny {
            description "Unsupported versions denied by default";
          }
        }
        default allow;
        description
          "Are unsupported versions not in version-exceptions allowed
           or denied?";
      }

      leaf-list version-exceptions {
        type uint32;
        description
          "Exceptions to the default-deny or default-allow rule.";
      }

      list token-keys {
        key "key-sequence-number";
        description
          "list of active keys, for key rotation purposes. Existence implies
           shared-state format";

        leaf key-sequence-number {
          type uint8;
          mandatory true;
          description
            "Identifies the key used to encrypt the token";
        }

        leaf token-key {
          type quic-lb-key;
          mandatory true;
          description
            "16-byte key to encrypt the token";
        }

        leaf token-iv {
          type yang:hex-string {
            length 23;

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          }
          mandatory true;
          description
            "8-byte IV to encrypt the token, encoded in 23 bytes";
        }
      }
    }
  }
}

A.1.  Tree Diagram

   This summary of the YANG model uses the notation in [RFC8340].

 module: ietf-quic-lb
   +--rw quic-lb
      +--rw cid-configs*
      |       [config-rotation-bits]
      |  +--rw config-rotation-bits             uint8
      |  +--rw first-octet-encodes-cid-length?  boolean
      |  +--rw cid-key?                         yang:hex-string
      |  +--rw nonce-length?                    uint8
      |  +--rw lb-timeout?                      uint32
      |  +--rw server-id-length                 uint8
      |  +--rw server-id-mappings*?
      |  |       [server-id]
      |  |  +--rw server-id                     yang:hex-string
      |  |  +--rw server-address                inet:ip-address
      +--ro retry-service-config
      |  +--rw supported-versions*
      |  |  +--rw version                       uint32
      |  +--rw unsupported-version-default      enumeration {allow deny}
      |  +--rw version-exceptions*
      |  |  +--rw version                       uint32
      |  +--rw token-keys*?
      |  |       [key-sequence-number]
      |  |  +--rw key-sequence-number           uint8
      |  |  +--rw token-key                     yang:hex-string
      |  |  +--rw token-iv                      yang:hex-string

Appendix B.  Load Balancer Test Vectors

   Each section of this draft includes multiple sets of load balancer
   configuration, each of which has five examples of server ID and
   server use bytes and how they are encoded in a CID.

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   In some cases, there are no server use bytes.  Note that, for
   simplicity, the first octet bits used for neither config rotation nor
   length self-encoding are random, rather than listed in the server use
   field.  Therefore, a server implementation using these parameters may
   generate CIDs with a slightly different first octet.

   This section uses the following abbreviations:

   cid      Connection ID
   cr_bits  Config Rotation Bits
   LB       Load Balancer
   sid      Server ID
   sid_len  Server ID length
   su       Server Use Bytes

   All values except length_self_encoding and sid_len are expressed in
   hexidecimal format.

B.1.  Plaintext Connection ID Algorithm

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   LB configuration: cr_bits 0x0 length_self_encoding: y sid_len 1

   cid 01be sid be su
   cid 0221b7 sid 21 su b7
   cid 03cadfd8 sid ca su dfd8
   cid 041e0c9328 sid 1e su 0c9328
   cid 050c8f6d9129 sid 0c su 8f6d9129

   LB configuration: cr_bits 0x0 length_self_encoding: n sid_len 2

   cid 02aab0 sid aab0 su
   cid 3ac4b106 sid c4b1 su 06
   cid 08bd3cf4a0 sid bd3c su f4a0
   cid 3771d59502d6 sid 71d5 su 9502d6
   cid 1d57dee8b888f3 sid 57de su e8b888f3

   LB configuration: cr_bits 0x0 length_self_encoding: y sid_len 3

   cid 0336c976 sid 36c976 su
   cid 04aa291806 sid aa2918 su 06
   cid 0586897bd8b6 sid 86897b su d8b6
   cid 063625bcae4de0 sid 3625bc su ae4de0
   cid 07966fb1f3cb535f sid 966fb1 su f3cb535f

   LB configuration: cr_bits 0x0 length_self_encoding: n sid_len 4

   cid 185172fab8 sid 5172fab8 su
   cid 2eb7ff2c9297 sid b7ff2c92 su 97
   cid 14f3eb3dd3edbe sid f3eb3dd3 su edbe
   cid 3feb31cece744b74 sid eb31cece su 744b74
   cid 06b9f34c353ce23bb5 sid b9f34c35 su 3ce23bb5

   LB configuration: cr_bits 0x0 length_self_encoding: y sid_len 5

   cid 05bdcd8d0b1d sid bdcd8d0b1d su
   cid 06aee673725a63 sid aee673725a su 63
   cid 07bbf338ddbf37f4 sid bbf338ddbf su 37f4
   cid 08fbbca64c26756840 sid fbbca64c26 su 756840
   cid 09e7737c495b93894e34 sid e7737c495b su 93894e34

B.2.  Stream Cipher Connection ID Algorithm

   In each case below, the server is using a plain text nonce value of
   zero.

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LB configuration: cr_bits 0x0 length_self_encoding: y nonce_len 12 sid_len 1
    key 4d9d0fd25a25e7f321ef464e13f9fa3d

cid 0d69fe8ab8293680395ae256e89c sid c5 su
cid 0e420d74ed99b985e10f5073f43027 sid d5 su 27
cid 0f380f440c6eefd3142ee776f6c16027 sid 10 su 6027
cid 1020607efbe82049ddbf3a7c3d9d32604d sid 3c su 32604d
cid 11e132d12606a1bb0fa17e1caef00ec54c10 sid e3 su 0ec54c10

LB configuration: cr_bits 0x0 length_self_encoding: n nonce_len 12 sid_len 2
    key 49e1cec7fd264b1f4af37413baf8ada9

cid 3d3a5e1126414271cc8dc2ec7c8c15 sid f7fe su
cid 007042539e7c5f139ac2adfbf54ba748 sid eaf4 su 48
cid 2bc125dd2aed2aafacf59855d99e029217 sid e880 su 9217
cid 3be6728dc082802d9862c6c8e4dda3d984d8 sid 62c6 su d984d8
cid 1afe9c6259ad350fc7bad28e0aeb2e8d4d4742 sid 8502 su 8d4d4742

LB configuration: cr_bits 0x0 length_self_encoding: y nonce_len 14 sid_len 3
    key 2c70df0b399bd33a7335523dcdb884ad

cid 11d62e8670565cd30b552edff6782ff5a740 sid d794bb su
cid 12c70e481f49363cabd9370d1fd5012c12bca5 sid 2cbd5d su a5
cid 133b95dfd8ad93566782f8424df82458069fc9e9 sid d126cd su c9e9
cid 13ac6ffcd635532ab60370306c7ee572d6b6e795 sid 539e42 su e795
cid 1383ed07a9700777ff450bb39bb9c1981266805c sid 9094dd su 805c

LB configuration: cr_bits 0x0 length_self_encoding: n nonce_len 12 sid_len 4
    key 2297b8a95c776cf9c048b76d9dc27019

cid 32873890c3059ca62628089439c44c1f84 sid 7398d8ca su
cid 1ff7c7d7b9823954b178636c99a7dc93ac83 sid 9655f091 su 83
cid 31044000a5ebb3bf2fa7629a17f2c78b077c17 sid 8b035fc6 su 7c17
cid 1791bd28c66721e8fea0c6f34fd2d8e663a6ef70 sid 6672e0e2 su a6ef70
cid 3df1d90ad5ccd5f8f475f040e90aeca09ec9839d sid b98b1fff su c9839d

LB configuration: cr_bits 0x0 length_self_encoding: y nonce_len 8 sid_len 5
    key 484b2ed942d9f4765e45035da3340423

cid 0da995b7537db605bfd3a38881ae sid 391a7840dc su
cid 0ed8d02d55b91d06443540d1bf6e98 sid 10f7f7b284 su 98
cid 0f3f74be6d46a84ccb1fd1ee92cdeaf2 sid 0606918fc0 su eaf2
cid 1045626dbf20e03050837633cc5650f97c sid e505eea637 su 50f97c
cid 11bb9a17f691ab446a938427febbeb593eaa sid 99343a2a96 su eb593eaa

B.3.  Block Cipher Connection ID Algorithm

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LB configuration: cr_bits 0x0 length_self_encoding: y sid_len 1
    key 411592e4160268398386af84ea7505d4

cid 10564f7c0df399f6d93bdddb1a03886f25 sid 23 su 05231748a80884ed58007847eb9fd0
cid 10d5c03f9dd765d73b3d8610b244f74d02 sid 15 su 76cd6b6f0d3f0b20fc8e633e3a05f3
cid 108ca55228ab23b92845341344a2f956f2 sid 64 su 65c0ce170a9548717498b537cb8790
cid 10e73f3d034aef2f6f501e3a7693d6270a sid 07 su f9ad10c84cc1e89a2492221d74e707
cid 101a6ce13d48b14a77ecfd365595ad2582 sid 6c su 76ce4689b0745b956ef71c2608045d

LB configuration: cr_bits 0x0 length_self_encoding: n sid_len 2
    key 92ce44aecd636aeeff78da691ef48f77

cid 20aa09bc65ed52b1ccd29feb7ef995d318 sid a52f su 99278b92a86694ff0ecd64bc2f73
cid 30b8dbef657bd78a2f870e93f9485d5211 sid 6c49 su 7381c8657a388b4e9594297afe96
cid 043a8137331eacd2e78383279b202b9a6d sid 4188 su 5ac4b0e0b95f4e7473b49ee2d0dd
cid 3ba71ea2bcf0ab95719ab59d3d7fde770d sid 8ccc su 08728807605db25f2ca88be08e0f
cid 37ef1956b4ec354f40dc68336a23d42b31 sid c89d su 5a3ccd1471caa0de221ad6c185c0

LB configuration: cr_bits 0x0 length_self_encoding: y sid_len 3
    key 5c49cb9265efe8ae7b1d3886948b0a34

cid 10efcffc161d232d113998a49b1dbc4aa0 sid 0690b3 su 958fc9f38fe61b83881b2c5780
cid 10fc13bdbcb414ba90e391833400c19505 sid 031ac3 su 9a55e1e1904e780346fcc32c3c
cid 10d3cc1efaf5dc52c7a0f6da2746a8c714 sid 572d3a su ff2ec9712664e7174dc03ca3f8
cid 107edf37f6788e33c0ec7758a485215f2b sid 562c25 su 02c5a5dcbea629c3840da5f567
cid 10bc28da122582b7312e65aa096e9724fc sid 2fa4f0 su 8ae8c666bfc0fc364ebfd06b9a

LB configuration: cr_bits 0x0 length_self_encoding: n sid_len 4
    key e787a3a491551fb2b4901a3fa15974f3

cid 26125351da12435615e3be6b16fad35560 sid 0cb227d3 su 65b40b1ab54e05bff55db046
cid 14de05fc84e41b611dfbe99ed5b1c9d563 sid 6a0f23ad su d73bee2f3a7e72b3ffea52d9
cid 1306052c3f973db87de6d7904914840ff1 sid ca21402d su 5829465f7418b56ee6ada431
cid 1d202b5811af3e1dba9ea2950d27879a92 sid b14e1307 su 4902aba8b23a5f24616df3cf
cid 26538b78efc2d418539ad1de13ab73e477 sid a75e0148 su 0040323f1854e75aeb449b9f

LB configuration: cr_bits 0x0 length_self_encoding: y sid_len 5
    key d5a6d7824336fbe0f25d28487cdda57c

cid 10a2794871aadb20ddf274a95249e57fde sid 82d3b0b1a1 su 0935471478c2edb8120e60
cid 108122fe80a6e546a285c475a3b8613ec9 sid fbcc902c9d su 59c47946882a9a93981c15
cid 104d227ad9dd0fef4c8cb6eb75887b6ccc sid 2808e22642 su 2a7ef40e2c7e17ae40b3fb
cid 10b3f367d8627b36990a28d67f50b97846 sid 5e018f0197 su 2289cae06a566e5cb6cfa4
cid 1024412bfe25f4547510204bdda6143814 sid 8a8dd3d036 su 4b12933a135e5eaaebc6fd

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Appendix C.  Acknowledgments

   The authors would like to thank Christian Huitema and Ian Swett for
   their major design contributions.

   Manasi Deval, Erik Fuller, Toma Gavrichenkov, Jana Iyengar, Subodh
   Iyengar, Ladislav Lhotka, Jan Lindblad, Ling Tao Nju, Kazuho Oku,
   Udip Pant, Martin Thomson, Dmitri Tikhonov, Victor Vasiliev, and
   William Zeng Ke all provided useful input to this document.

Appendix D.  Change Log

      *RFC Editor's Note:* Please remove this section prior to
      publication of a final version of this document.

D.1.  since draft-ietf-quic-load-balancers-05

   *  Added low-config CID for further discussion

   *  Complete revision of shared-state Retry Token

   *  Added YANG model

   *  Updated configuration limits to ensure CID entropy

   *  Switched to notation from quic-transport

D.2.  since draft-ietf-quic-load-balancers-04

   *  Rearranged the shared-state retry token to simplify token
      processing

   *  More compact timestamp in shared-state retry token

   *  Revised server requirements for shared-state retries

   *  Eliminated zero padding from the test vectors

   *  Added server use bytes to the test vectors

   *  Additional compliant DCID criteria

D.3.  since-draft-ietf-quic-load-balancers-03

   *  Improved Config Rotation text

   *  Added stream cipher test vectors

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   *  Deleted the Obfuscated CID algorithm

D.4.  since-draft-ietf-quic-load-balancers-02

   *  Replaced stream cipher algorithm with three-pass version

   *  Updated Retry format to encode info for required TPs

   *  Added discussion of version invariance

   *  Cleaned up text about config rotation

   *  Added Reset Oracle and limited configuration considerations

   *  Allow dropped long-header packets for known QUIC versions

D.5.  since-draft-ietf-quic-load-balancers-01

   *  Test vectors for load balancer decoding

   *  Deleted remnants of in-band protocol

   *  Light edit of Retry Services section

   *  Discussed load balancer chains

D.6.  since-draft-ietf-quic-load-balancers-00

   *  Removed in-band protocol from the document

D.7.  Since draft-duke-quic-load-balancers-06

   *  Switch to IETF WG draft.

D.8.  Since draft-duke-quic-load-balancers-05

   *  Editorial changes

   *  Made load balancer behavior independent of QUIC version

   *  Got rid of token in stream cipher encoding, because server might
      not have it

   *  Defined "non-compliant DCID" and specified rules for handling
      them.

   *  Added psuedocode for config schema

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D.9.  Since draft-duke-quic-load-balancers-04

   *  Added standard for retry services

D.10.  Since draft-duke-quic-load-balancers-03

   *  Renamed Plaintext CID algorithm as Obfuscated CID

   *  Added new Plaintext CID algorithm

   *  Updated to allow 20B CIDs

   *  Added self-encoding of CID length

D.11.  Since draft-duke-quic-load-balancers-02

   *  Added Config Rotation

   *  Added failover mode

   *  Tweaks to existing CID algorithms

   *  Added Block Cipher CID algorithm

   *  Reformatted QUIC-LB packets

D.12.  Since draft-duke-quic-load-balancers-01

   *  Complete rewrite

   *  Supports multiple security levels

   *  Lightweight messages

D.13.  Since draft-duke-quic-load-balancers-00

   *  Converted to markdown

   *  Added variable length connection IDs

Authors' Addresses

   Martin Duke
   F5 Networks, Inc.

   Email: martin.h.duke@gmail.com

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   Nick Banks
   Microsoft

   Email: nibanks@microsoft.com

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