QUIC                                                             M. Duke
Internet-Draft                                         F5 Networks, Inc.
Intended status: Standards Track                                N. Banks
Expires: 3 May 2021                                            Microsoft
                                                         30 October 2020

            QUIC-LB: Generating Routable QUIC Connection IDs


   QUIC connection IDs allow continuation of connections across address/
   port 4-tuple changes, and can store routing information for stateless
   or low-state load balancers.  They also can prevent linkability of
   connections across deliberate address migration through the use of
   protected communications between client and server.  This creates
   issues for load-balancing intermediaries.  This specification
   standardizes methods for encoding routing information given a small
   set of configuration parameters.  This framework also enables offload
   of other QUIC functions to trusted intermediaries, given the explicit
   cooperation of the QUIC 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
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   This Internet-Draft will expire on 3 May 2021.

Copyright Notice

   Copyright (c) 2020 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
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Protocol Objectives . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Simplicity  . . . . . . . . . . . . . . . . . . . . . . .   5
     2.2.  Security  . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  First CID octet . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Config Rotation . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Configuration Failover  . . . . . . . . . . . . . . . . .   7
     3.3.  Length Self-Description . . . . . . . . . . . . . . . . .   7
     3.4.  Format  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   4.  Routing Algorithms  . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Plaintext CID Algorithm . . . . . . . . . . . . . . . . .   9
       4.1.1.  Configuration Agent Actions . . . . . . . . . . . . .   9
       4.1.2.  Load Balancer Actions . . . . . . . . . . . . . . . .  10
       4.1.3.  Server Actions  . . . . . . . . . . . . . . . . . . .  10
     4.2.  Stream Cipher CID Algorithm . . . . . . . . . . . . . . .  10
       4.2.1.  Configuration Agent Actions . . . . . . . . . . . . .  10
       4.2.2.  Load Balancer Actions . . . . . . . . . . . . . . . .  11
       4.2.3.  Server Actions  . . . . . . . . . . . . . . . . . . .  12
     4.3.  Block Cipher CID Algorithm  . . . . . . . . . . . . . . .  12
       4.3.1.  Configuration Agent Actions . . . . . . . . . . . . .  13
       4.3.2.  Load Balancer Actions . . . . . . . . . . . . . . . .  13
       4.3.3.  Server Actions  . . . . . . . . . . . . . . . . . . .  13
   5.  ICMP Processing . . . . . . . . . . . . . . . . . . . . . . .  13
   6.  Retry Service . . . . . . . . . . . . . . . . . . . . . . . .  14
     6.1.  Common Requirements . . . . . . . . . . . . . . . . . . .  14
     6.2.  No-Shared-State Retry Service . . . . . . . . . . . . . .  15
       6.2.1.  Configuration Agent Actions . . . . . . . . . . . . .  15
       6.2.2.  Service Requirements  . . . . . . . . . . . . . . . .  15
       6.2.3.  Server Requirements . . . . . . . . . . . . . . . . .  17
     6.3.  Shared-State Retry Service  . . . . . . . . . . . . . . .  17
       6.3.1.  Configuration Agent Actions . . . . . . . . . . . . .  19
       6.3.2.  Service Requirements  . . . . . . . . . . . . . . . .  19
       6.3.3.  Server Requirements . . . . . . . . . . . . . . . . .  20
   7.  Configuration Requirements  . . . . . . . . . . . . . . . . .  20
   8.  Additional Use Cases  . . . . . . . . . . . . . . . . . . . .  22
     8.1.  Load balancer chains  . . . . . . . . . . . . . . . . . .  22
     8.2.  Moving connections between servers  . . . . . . . . . . .  23
   9.  Version Invariance of QUIC-LB . . . . . . . . . . . . . . . .  23
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  24

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     10.1.  Attackers not between the load balancer and server . . .  24
     10.2.  Attackers between the load balancer and server . . . . .  25
     10.3.  Multiple Configuration IDs . . . . . . . . . . . . . . .  25
     10.4.  Limited configuration scope  . . . . . . . . . . . . . .  25
     10.5.  Stateless Reset Oracle . . . . . . . . . . . . . . . . .  25
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  26
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  26
     12.2.  Informative References . . . . . . . . . . . . . . . . .  26
   Appendix A.  Load Balancer Test Vectors . . . . . . . . . . . . .  26
     A.1.  Plaintext Connection ID Algorithm . . . . . . . . . . . .  27
     A.2.  Stream Cipher Connection ID Algorithm . . . . . . . . . .  27
     A.3.  Block Cipher Connection ID Algorithm  . . . . . . . . . .  28
   Appendix B.  Acknowledgments  . . . . . . . . . . . . . . . . . .  30
   Appendix C.  Change Log . . . . . . . . . . . . . . . . . . . . .  30
     C.1.  since draft-ietf-quic-load-balancers-04 . . . . . . . . .  30
     C.2.  since-draft-ietf-quic-load-balancers-03 . . . . . . . . .  30
     C.3.  since-draft-ietf-quic-load-balancers-02 . . . . . . . . .  30
     C.4.  since-draft-ietf-quic-load-balancers-01 . . . . . . . . .  31
     C.5.  since-draft-ietf-quic-load-balancers-00 . . . . . . . . .  31
     C.6.  Since draft-duke-quic-load-balancers-06 . . . . . . . . .  31
     C.7.  Since draft-duke-quic-load-balancers-05 . . . . . . . . .  31
     C.8.  Since draft-duke-quic-load-balancers-04 . . . . . . . . .  31
     C.9.  Since draft-duke-quic-load-balancers-03 . . . . . . . . .  31
     C.10. Since draft-duke-quic-load-balancers-02 . . . . . . . . .  32
     C.11. Since draft-duke-quic-load-balancers-01 . . . . . . . . .  32
     C.12. Since draft-duke-quic-load-balancers-00 . . . . . . . . .  32
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  32

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.

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   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.

   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",
   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.

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   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".

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

   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 10.3).

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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

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |C R|  CID Len  |

                        Figure 1: First Octet Format

   The first octet has the following fields:

   CR: Config Rotation bits.

   CID Len: Length Self-Description (if applicable).  Encodes the length
   of the Connection ID following the First Octet.

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4.  Routing Algorithms

   In QUIC-LB, load balancers do not generate individual connection IDs
   to 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.

   As clients sometimes generate the DCIDs in long headers, these might
   not conform to the expectations of the routing algorithm.  These are
   called "non-compliant DCIDs":

   *  The DCID might not be long enough for the routing algorithm to

   *  The config rotation bits (Section 3.1) may not correspond to an
      active configuration.

   *  The extracted server mapping might not correspond to an active

   Load balancers MUST forward packets with long headers and non-
   compliant DCIDs to an active server using an algorithm of its own
   choosing.  It need not coordinate this algorithm with the servers.
   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.  For example, a non-compliant DCID might be converted 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.  See also
   Section 9.

   As a partial exception to the above, 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.  The prohibition against dropping packets with long headers
   remains for unknown QUIC versions.

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

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   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.

   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.

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

   The load balancer 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 cannot base their design on version-
   specific templates.

   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.

   This section describes three participants: the configuration agent,
   the load balancer, and the server.

4.1.  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.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |  First octet  |             Server ID (X=8..152)              |
   |                        Any (0..152-X)                         |

                       Figure 2: Plaintext CID Format

4.1.1.  Configuration Agent Actions

   The configuration agent selects a length for the server ID encoding.
   This length MUST have enough entropy to have a different code point
   for each server.

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   It also assigns a server ID to each server.

4.1.2.  Load Balancer Actions

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

4.1.3.  Server Actions

   The server chooses a connection ID length.  This MUST be at least one
   byte longer than the routing bytes.

   When a server needs a new connection ID, it encodes its assigned
   server ID 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.

4.2.  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

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |  First Octet  |            Nonce (X=64..128)                  |
   |                 Encrypted Server ID (Y=8..152-X)              |
   |                   For server use (0..152-X-Y)                 |

                     Figure 3: Stream Cipher CID Format

4.2.1.  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.

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4.2.2.  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:

   *  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

   server_id_intermediate = encrypted_server_id ^ AES-ECB(key, padded-

   *  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.

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   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.

4.2.3.  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

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

   The server encrypts the server ID using exactly the algorithm as
   described in Section 4.2.2, performing the three passes in reverse

4.3.  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.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |  First octet  |       Encrypted server ID (X=8..128)          |
   |           Encrypted bits for server use (128-X)               |
   |           Unencrypted bits for server use (0..24)             |

                     Figure 4: Block Cipher CID Format

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4.3.1.  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 server ID will start in the second octet of the decrypted
   connection ID and occupy continuous octets beyond that.

   They server ID length MUST be no more than 16 octets and SHOULD be no
   more than 12 octets, to provide servers adequate space to encode
   their own opaque data.

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

4.3.2.  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.

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

4.3.3.  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
   provided server ID into the server ID octets and arbitrary bits into
   the remaining bits.  These arbitrary bits MAY encode additional
   information.  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.

5.  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.

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   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

6.  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.

   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.

6.1.  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

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   A retry service MUST forward all packets for a QUIC version it does
   not understand.  Note that if servers support versions the retry
   service does not, this may increase load on the servers.  However,
   dropping these packets would introduce chokepoints to block
   deployment of new QUIC versions.  Note that future versions of QUIC
   might not have Retry packets, require different information in Retry,
   or use different packet type indicators.

6.2.  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

6.2.1.  Configuration Agent Actions

   The configuration agent distributes a list of QUIC versions to be
   served by the Retry Service.

6.2.2.  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.

   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.

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   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |0| ODCIL (7) |   RSCIL (8)   |
   |        Original Destination Connection ID (0..160)            |
   |                             ...                               |
   |              Retry Source Connection ID (0..160)              |
   |                             ...                               |
   |                     Opaque Data (variable)                    |

         Figure 5: 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.

   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

   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

   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
   successful, the service MUST forward the packet with the token

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   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.

6.2.3.  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 6.2.2.

6.3.  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

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

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   All tokens, generated by either the server or retry service, MUST use
   the following format.  This format is the cleartext version.  On the
   wire, these fields are encrypted using an AES-ECB cipher and the
   token key.  If the token is not a multiple of 16 octets, the last
   block is padded with zeroes.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |                                                               |
   +                                                               +
   |                                                               |
   +                    Client IP Address (128)                    +
   |                                                               |
   +                                                               +
   |                                                               |
   |    ODCIL    |      RSCIL    |
   |        Original Destination Connection ID (0..160)            |
   |                             ...                               |
   |              Retry Source Connection ID (0..160)              |
   |                             ...                               |
   |                                                               |
   +                        Timestamp (64)                         +
   |                                                               |
   |                      Opaque Data (optional)                   |

          Figure 6: Cleartext format of shared-state retry tokens

   The tokens have 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.

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

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

   Client IP Address: 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.

   Timestamp: The timestamp is a 64-bit integer, in network order, that
   expresses the number of seconds in POSIX time (see Sec. 4.16 of

   Opaque Data: The server may use this field to encode additional
   information, such as congestion window, RTT, or MTU.  Opaque data MAY
   also allow servers to distinguish between retry tokens (which trigger
   use of certain transport parameters) and NEW_TOKEN frame tokens.

6.3.1.  Configuration Agent Actions

   The configuration agent generates and distributes a "token key" and a
   list of QUIC versions the service supports.  It must also inform the
   service if a NAT lies between the service and the servers.

6.3.2.  Service Requirements

   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.

   In active mode, the service SHOULD decrypt the first 16 octets of
   incoming tokens.  The service SHOULD drop packets with an IP address
   that does not match, and SHOULD forward packets that do, regardless
   of the other fields.

   However, the service MUST NOT decrypt or validate tokens if there is
   a NAT between it and the servers.

   In inactive mode, the service SHOULD forward all packets to the
   server so that the server can issue an up-to-date token to the

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6.3.3.  Server Requirements

   When issuing Retry or NEW_TOKEN tokens, the server MUST encode the
   client IP address in the first 16 octets and encrypt that block with
   the token key.  It MAY use any format or encryption for the remainder
   of the token.  However, it MUST include a means of distinguishing
   service-generated Retry tokens, server-generated Retry tokens (if
   different), and NEW_TOKEN 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
   future, due to possible clock synchronization issues.

   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

   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.

7.  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 and
   the relevant parameters for that algorithm.  Each server MUST know
   its server ID for each configuration, and the load balancer MUST have
   forwarding instructions for each server ID.

   For all algorithms, the load balancer and servers MUST have a common
   understanding of the server ID length.

   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.

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   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.  A shared-state Retry Service also needs
   the token key, and to be aware if a NAT sits between it and the

   The following pseudocode describes the data items necessary to store
   a full QUIC-LB configuration at the server.  It is meant to describe
   the conceptual range and not specify the presentation of such
   configuration in an internet packet.  The comments signify the range
   of acceptable values where applicable.

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    uint2    config_rotation_bits;
    boolean  first_octet_encodes_cid_length;
    enum     { none, non_shared_state, shared_state } retry_service;
    select (retry_service) {
        case none: null;
        case non_shared_state: uint32 list_of_quic_versions[];
        case shared_state: {
            uint32   list_of_quic_versions[];
            uint8    token_key[16];
        } shared_state_config;
    } retry_service_config;
    enum     { none, plaintext, stream_cipher, block_cipher }
    select (routing_algorithm) {
        case none: null;
        case plaintext: struct {
            uint8 server_id_length; /* 1..19 */
            uint8 server_id[server_id_length];
        } plaintext_config;
        case stream_cipher: struct {
            uint8  nonce_length; /* 8..16 */
            uint8  server_id_length; /* 1..(19 - nonce_length) */
            uint8  server_id[server_id_length];
            uint8  key[16];
        } stream_cipher_config;
        case block_cipher: struct {
            uint8  server_id_length;
            uint8  server_id[server_id_length];
            uint8  key[16];
        } block_cipher_config;
   } routing_algorithm_config;

8.  Additional Use Cases

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

8.1.  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

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   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.

8.2.  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.

9.  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

   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 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-

   *  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.

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   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.

10.  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.

10.1.  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.

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10.2.  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.

10.3.  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.

10.4.  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 10.3.

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

10.5.  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.

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11.  IANA Considerations

   There are no IANA requirements.

12.  References

12.1.  Normative References

              Thomson, M., Ed., "Version-Independent Properties of
              QUIC", Work in Progress, Internet-Draft, draft-ietf-quic-

              Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", Work in Progress,
              Internet-Draft, draft-ietf-quic-transport,

   [TIME_T]   "Open Group Standard: Vol. 1: Base Definitions, Issue 7",
              IEEE Std 1003.1 , 2018,

12.2.  Informative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

Appendix A.  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.

   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

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

A.1.  Plaintext Connection ID Algorithm

   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

   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

A.2.  Stream Cipher Connection ID Algorithm

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

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

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   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

A.3.  Block Cipher Connection ID Algorithm

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

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   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

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

   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

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

   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

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

   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

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

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   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

Appendix B.  Acknowledgments

Appendix C.  Change Log

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

C.1.  since draft-ietf-quic-load-balancers-04

   *  Rearranged the shared-state retry token to simplify token

   *  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

C.2.  since-draft-ietf-quic-load-balancers-03

   *  Improved Config Rotation text

   *  Added stream cipher test vectors

   *  Deleted the Obfuscated CID algorithm

C.3.  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

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   *  Added Reset Oracle and limited configuration considerations

   *  Allow dropped long-header packets for known QUIC versions

C.4.  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

C.5.  since-draft-ietf-quic-load-balancers-00

   *  Removed in-band protocol from the document

C.6.  Since draft-duke-quic-load-balancers-06

   *  Switch to IETF WG draft.

C.7.  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

   *  Added psuedocode for config schema

C.8.  Since draft-duke-quic-load-balancers-04

   *  Added standard for retry services

C.9.  Since draft-duke-quic-load-balancers-03

   *  Renamed Plaintext CID algorithm as Obfuscated CID

   *  Added new Plaintext CID algorithm

   *  Updated to allow 20B CIDs

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   *  Added self-encoding of CID length

C.10.  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

C.11.  Since draft-duke-quic-load-balancers-01

   *  Complete rewrite

   *  Supports multiple security levels

   *  Lightweight messages

C.12.  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

   Nick Banks

   Email: nibanks@microsoft.com

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