QUIC-LB: Generating Routable QUIC Connection IDs
draft-duke-quic-load-balancers-03

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QUIC                                                             M. Duke
Internet-Draft                                         F5 Networks, Inc.
Intended status: Standards Track                       December 10, 2018
Expires: June 13, 2019

            QUIC-LB: Generating Routable QUIC Connection IDs
                   draft-duke-quic-load-balancers-03

Abstract

   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 and proposes an
   optional protocol called QUIC_LB to exchange the parameters of that
   encoding.

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 June 13, 2019.

Copyright Notice

   Copyright (c) 2018 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.  Please review these documents
   carefully, as they describe your rights and restrictions with respect

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   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Protocol Objectives . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Simplicity  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Security  . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Robustness to Middleboxes . . . . . . . . . . . . . . . .   5
     2.4.  Load Balancer Chains  . . . . . . . . . . . . . . . . . .   5
   3.  Routing Algorithms  . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Plaintext CID Algorithm . . . . . . . . . . . . . . . . .   6
       3.1.1.  Load Balancer Actions . . . . . . . . . . . . . . . .   6
       3.1.2.  Server Actions  . . . . . . . . . . . . . . . . . . .   7
     3.2.  Stream Cipher CID Algorithm . . . . . . . . . . . . . . .   7
       3.2.1.  Load Balancer Actions . . . . . . . . . . . . . . . .   8
       3.2.2.  Server Actions  . . . . . . . . . . . . . . . . . . .   8
     3.3.  Block Cipher CID Algorithm  . . . . . . . . . . . . . . .   9
     3.4.  Load Balancer Actions . . . . . . . . . . . . . . . . . .   9
       3.4.1.  Server Actions  . . . . . . . . . . . . . . . . . . .   9
   4.  Protocol Description  . . . . . . . . . . . . . . . . . . . .  10
     4.1.  Out of band sharing . . . . . . . . . . . . . . . . . . .  10
     4.2.  QUIC-LB Message Exchange  . . . . . . . . . . . . . . . .  10
     4.3.  QUIC-LB Packet  . . . . . . . . . . . . . . . . . . . . .  11
     4.4.  Message Types and Formats . . . . . . . . . . . . . . . .  12
       4.4.1.  ACK_LB Message  . . . . . . . . . . . . . . . . . . .  12
       4.4.2.  FAIL Message  . . . . . . . . . . . . . . . . . . . .  12
       4.4.3.  ROUTING_INFO Message  . . . . . . . . . . . . . . . .  12
       4.4.4.  STREAM_CID Message  . . . . . . . . . . . . . . . . .  13
       4.4.5.  BLOCK_CID Message . . . . . . . . . . . . . . . . . .  14
       4.4.6.  SERVER_ID Message . . . . . . . . . . . . . . . . . .  15
       4.4.7.  MODULUS Message . . . . . . . . . . . . . . . . . . .  15
   5.  Config Rotation . . . . . . . . . . . . . . . . . . . . . . .  15
     5.1.  Configuration Failover  . . . . . . . . . . . . . . . . .  16
   6.  Configuration Requirements  . . . . . . . . . . . . . . . . .  16
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
     7.1.  Outside attackers . . . . . . . . . . . . . . . . . . . .  17
     7.2.  Inside Attackers  . . . . . . . . . . . . . . . . . . . .  18
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  18
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  18
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  18
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  18

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     B.1.  Since draft-duke-quic-load-balancers-02 . . . . . . . . .  19
     B.2.  Since draft-duke-quic-load-balancers-01 . . . . . . . . .  19
     B.3.  Since draft-duke-quic-load-balancers-00 . . . . . . . . .  19
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   QUIC packets 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 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 a method of coordination between QUIC
   servers and low-state load balancers to support connection IDs that
   encode routing information.  It describes desirable properties of a
   solution, and then specifies a protocol that provides those
   properties.  This protocol supports multiple encoding schemes that
   increase in complexity as they address paths between load balancer
   and server with weaker trust dynamics.

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].

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   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.

   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.

   When discussing security threats to QUIC-LB, we distinguish between
   "inside observers" and "outside observers."  The former lie on the
   path between the load balancer and server, which often but not always
   lies inside the server's data center or cloud deployment.  Outside
   observers are on the path between the load balancer and client.
   "Off-path" attackers, though not on any data path, may also be
   "inside" or "outside" depending on whether not they have network
   access to the server without intermediation by the load balancer and/
   or other security devices.

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 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

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   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.

   However, concealing this mapping from inside observers is beyond the
   scope of QUIC-LB.  By simply observing Link-Layer and/or Network-
   Layer addresses of packets containing distinct connection IDs, it is
   trivial to determine that they map to the same server, even if
   connection IDs are entirely random and do not encode routing
   information.  Schemes that conceal these addresses (e.g., IPsec) can
   also conceal QUIC-LB messages.

   Inside observers are generally able to mount Denial of Service (DoS)
   attacks on QUIC connections regardless of Connection ID schemes.
   However, QUIC-LB should protect against Denial of Service due to
   inside off-path attackers in cases where such attackers are possible.

   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.

2.3.  Robustness to Middleboxes

   The path between load balancer and server may pass through
   middleboxes that could drop the coordination messages in this
   protocol.  It is therefore advantageous to make messages resemble
   QUIC traffic as much as possible, as any viable path must obviously
   admit QUIC traffic.

2.4.  Load Balancer Chains

   While it is possible to construct a scheme that supports multiple
   low-state load balancers in the path, by using different parts of the
   connection ID to encoding routing information for each load balancer,
   this use case is out of scope for QUIC-LB.

3.  Routing Algorithms

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

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

   The load balancer SHOULD route Initial and 0-RTT packets from the
   client using an alternate algorithm.  Note that the SCID in these
   packets may not be long enough to represent all the routing bits.
   This algorithm SHOULD generate consistent results for Initial and
   0RTT packets that arrive with the same source and destination
   connection ID.  The load balancer algorithms below apply to all
   incoming Handshake and 1-RTT packets.

   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 SCIDs over these schemes.

3.1.  Plaintext CID Algorithm

3.1.1.  Load Balancer Actions

   The load balancer selects an arbitrary set of bits of the server
   connection ID (SCID) that it will use to route to a given server,
   called the "routing bits".  The number of bits MUST have enough
   entropy to have a different code point for each server, and SHOULD
   have enough entropy so that there are many codepoints for each
   server.

   The load balancer MUST NOT select a routing mask that with more than
   126 routing bits set to 1, which allows at least 2 bits for config
   rotation (see Section 5) and 16 for server purposes in a maximum-
   length connection ID.

   The first two bits of an SCID MUST NOT be routing bits; these are
   reserved for config rotation.

   The load balancer selects a divisor that MUST be larger than the
   number of servers.  It SHOULD be large enough to accommodate
   reasonable increases in the number of servers.  The divisor MUST be
   an odd integer so certain addition operations do not always produce
   an even number.

   The load balancer also assigns each server a "modulus", an integer
   between 0 and the divisor minus 1.  These MUST be unique for each
   server, and SHOULD be distributed across the entire number space
   between zero and the divisor.

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   The load balancer shares these three values with servers, as
   explained in Section 4.

   Upon receipt of a QUIC packet that is not of type Initial or 0-RTT,
   the load balancer extracts the selected bits of the SCID and
   expresses them as an unsigned integer of that length.  The load
   balancer then divides the result by the chosen divisor.  The modulus
   of this operation maps to the modulus for the destination server.

   Note that any SCID that contains a server's modulus, plus an
   arbitrary integer multiple of the divisor, in the routing bits is
   routable to that server regardless of the contents of the non-routing
   bits.  Outside observers that do not know the divisor or the routing
   bits will therefore have difficulty identifying that two SCIDs route
   to the same server.

   Note also that not all Connection IDs are necessarily routable, as
   the computed modulus may not match one assigned to any server.  Load
   balancers SHOULD drop these packets if not a QUIC Initial or 0-RTT
   packet.

3.1.2.  Server Actions

   The server chooses a connection ID length.  This MUST contain all of
   the routing bits and MUST be at least 8 octets to provide adequate
   entropy.

   When a server needs a new connection ID, it adds an arbitrary
   nonnegative integer multiple of the divisor to its modulus, without
   exceeding the maximum integer value implied by the number of routing
   bits.  The choice of multiple should appear random within these
   constraints.

   The server encodes the result in the routing bits.  It MAY put any
   other value into the non-routing bits except the config rotation
   bits.  The non-routing bits SHOULD appear random to observers.

3.2.  Stream Cipher CID Algorithm

   The Encrypted CID algorithm provides true cryptographic protection,
   rather than mere obfuscation, at the cost of additional per-packet
   processing at the load balancer to decrypt every incoming connection
   ID except for Initial and 0RTT packets.

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3.2.1.  Load Balancer Actions

   The load balancer 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 load balancer also selects a nonce length and an 16-octet AES-CTR
   key to use for connection ID decryption.  The nonce length MUST be at
   least eight octets and no more than 16 octets.  The nonce length and
   server ID length MUST sum to 18 or fewer octets.

   The load balancer shares these three values with servers, as
   explained in Section 4.

   Upon receipt of a QUIC packet that is not of type Initial or 0-RTT,
   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 server ID using 128-bit AES in counter
   (CTR) mode, much like QUIC packet number decryption.  The nonce
   octets are padded to 16 octets using the as many of the first octets
   of the token as necessary, and used as counter input to AES-CTR.

   server_id = AES-CTR(key, padded-nonce, encrypted_server_id)

   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 12 octets.
   The load balancer uses the first 10 octets (including the config
   rotation bits) of the connection ID for the nonce, pads it to 16
   octets using the first 6 octets of the token, and uses this to
   decrypt the server ID in the eleventh and twelfth octet.

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

3.2.2.  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 nonce and additional bits MAY
   encode additional information, but SHOULD appear essentially random
   to observers.  The first two bits of the first octet are reserved for
   config rotation Section 5, but form part of the nonce.

   The server then encrypts the server ID octets using 128-bit AES in
   counter (CTR) mode, much like QUIC packet number encryption.  The

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   server pads its nonce to 16 octets using the earliest octets of the
   token, and uses the result as the counter input to AES-CTR.

   encrypted_server_id = AES-CTR(key, padded-nonce, server-id)

3.3.  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 spurious connection IDs.  However, it
   also requires connection IDs of at least 17 octets, increasing
   overhead of client-to-server packets.

3.4.  Load Balancer Actions

   The load balancer 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.

   The load balancer selects a zero-padding length.  This SHOULD be at
   least four octets to allow detection of spurious connection IDs.  The
   server ID and zero- padding length MUST sum to no more than 16
   octets.  They SHOULD sum to no more than 12 octets, to provide
   servers adequate space to encode their own opaque data.

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

   The load balancer shares these four values with servers, as explained
   in Section 4.

   Upon receipt of a QUIC packet that is not of type Initial or 0-RTT,
   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, zero padding, and
   opaque server data in that order.  If the zero padding octets are not
   zero, the load balancer MUST drop the packet.  The load balancer uses
   the server ID octets for routing.

3.4.1.  Server Actions

   When generating a routable connection ID, the server MUST choose a
   connection ID length of 17 or 18 octets.  The server writes its
   provided server ID into the server ID octets, zeroes into the zero-

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   padding octets, and arbitrary bits into the remaining bits.  These
   arbitrary bits MAY encode additional information.  Bits in the first
   and eighteenth octets SHOULD appear essentially random to observers.
   The first two bits of the first octet are reserved for config
   rotation Section 5.

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

4.  Protocol Description

   The fundamental protocol requirement is to share the choice of
   routing algorithm, and the relevant parameters for that algorithm,
   between load balancer and server.

   For Plaintext CID Routing, this consists of the Routing Bits,
   Divisor, and Modulus.  The Modulus is unique to each server, but the
   others MUST be global.

   For Stream Cipher CID Routing, this consists of the Server ID, Server
   ID Length, Key, and Nonce Length.  The Server ID is unique to each
   server, but the others MUST be global.  The authentication token MUST
   be distributed out of band for this algorithm to operate.

   For Block Cipher CID Routing, this consists of the Server ID, Server
   ID Length, Key, and Zero-Padding Length.  The Server ID is unique to
   each server, but the others MUST be global.

   Each routing configuration also requires a unique two-bit config
   rotation codepoint (see Section 5) to identify it.

4.1.  Out of band sharing

   When there are concerns about the integrity of the path between load
   balancer and server, operators MAY share routing information using an
   out-of-band technique, which is out of the scope of this
   specification.

   To simplify configuration, the global parameters can be shared out-
   of-band, while the load balancer sends the unique server IDs via the
   truncated message formats presented below.

4.2.  QUIC-LB Message Exchange

   QUIC-LB load balancers and servers exchange messages via the QUIC-
   LBv1 protocol, which uses the QUIC invariants with version number
   0xF1000000.  The QUIC-LB load balancers send the encoding parameters
   to servers and periodically retransmit until that server responds

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   with an acknowledgement.  Specifics of this retransmission are
   implementation-dependent.

4.3.  QUIC-LB Packet

   A QUIC-LB packet uses a long header.  It carries configuration
   information from the load balancer and acknowledgements from the
   servers.  They are sent when a load balancer boots up, detects a new
   server in the pool or needs to update the server configuration.

   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
   +-+-+-+-+-+-+-+-+
   |1|C R| Reserved|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Version (32)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  0x00 | 0x00  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                  Authentication Token (64)                    +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Message Type  |
   +-+-+-+-+-+-+-+-+

                      Figure 1: QUIC-LB Packet Format

   The Version field allows QUIC-LB to use the Version Negotiation
   mechanism.  All messages in this specification are specific to QUIC-
   LBv1.  It should be set to 0xF1000000.

   Load balancers MUST cease sending QUIC-LB packets of this version to
   a server when that server sends a Version Negotiation packet that
   does not advertise the version.

   The length of the DCIL and SCIL fields are 0x00.

   CR The 2-bit.  CR field indicates the Config Rotation described in
      Section 5.

   Authentication Token  The Authentication Token is an 8-byte field
      that both entities obtain at configuration time.  It is used to
      verify that the sender is not an inside off-path attacker.
      Servers and load balancers SHOULD silently discard QUIC-LB packets
      with an incorrect token.

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   Message Type  The Message Type indicates the type of message payload
      that follows the QUIC-LB header.

4.4.  Message Types and Formats

   As described in Section 4.3, QUIC-LB packets contain a single
   message.  This section describes the format and semantics of the
   QUIC-LB message types.

4.4.1.  ACK_LB Message

   A server uses the ACK_LB message (type=0x00) to acknowledge a QUIC-LB
   packet received from the load balancer.  The ACK-LB message has no
   additional payload beyond the QUIC-LB packet header.

   Load balancers SHOULD continue to retransmit a QUIC-LB packet until a
   valid ACK_LB message, FAIL message or Version Negotiation Packet is
   received from the server.

4.4.2.  FAIL Message

   A server uses the FAIL message (type=0x01) to indicate the
   configuration received from the load balancer is unsupported.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Supp. Type  |  Supp. Type   |  ...
   +-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Servers MUST send a FAIL message upon receipt of a message type which
   they do not support, or if they do not possess all of the implied
   out-of-band configuration to support a particular message type.

   The payload of the FAIL message consists of a list of all the message
   types supported by the server.

   Upon receipt of a FAIL message, Load Balancers MUST either send a
   QUIC-LB message the server supports or remove the server from the
   server pool.

4.4.3.  ROUTING_INFO Message

   A load balancer uses the ROUTING_INFO message (type=0x02) to exchange
   all the parameters for the plaintext CID algorithm.

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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                       Routing Bit Mask (144)                  +
   |                                                               |
   +                                                               +
   |                                                               |
   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |         Modulus (16)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Divisor (16)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Routing Bit Mask  The Routing Bit Mask encodes a '1' at every bit
      position in the server connection ID that will encode routing
      information.

   These bits, along with the Modulus and Divisor, are chosen by the
   load balancer as described in Section 3.1.

4.4.4.  STREAM_CID Message

   A load balancer uses the STREAM_CID message (type=0x03) to exchange
   all the parameters for using Stream Cipher CIDs.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Nonce Len (8) |    SIDL (8)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Server ID (variable)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                             Key (128)                         +
   |                                                               |
   +                                                               +
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 2: Stream CID Payload

   Nonce Len  The Nonce Len field is a one-octet unsigned integer that
      describes the nonce length necessary to use this routing
      algorithm, in octets.

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   SIDL  The SIDL field is a one-octet unsigned integer that describes
      the server ID length necessary to use this routing algorithm, in
      octets.

   Server ID  The Server ID is the unique value assigned to the
      receiving server.  Its length is determined by the SIDL field.

   Key  The Key is an 16-octet field that contains the key that the load
      balancer will use to decrypt server IDs on QUIC packets.  See
      Section 7 to understand why sending keys in plaintext may be a
      safe strategy.

4.4.5.  BLOCK_CID Message

   A load balancer uses the BLOCK_CID message (type=0x04) to exchange
   all the parameters for using Stream Cipher CIDs.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   ZP Len (8)  |    SIDL (8)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Server ID (variable)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                             Key (128)                         +
   |                                                               |
   +                                                               +
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 3: Block CID Payload

   ZP Len  The ZP Len field is a one-octet unsigned integer that
      describes the zero-padding length necessary to use this routing
      algorithm, in octets.

   SIDL  The SIDL field is a one-octet unsigned integer that describes
      the server ID length necessary to use this routing algorithm, in
      octets.

   Server ID  The Server ID is the unique value assigned to the
      receiving server.  Its length is determined by the SIDL field.

   Key  The Key is an 16-octet field that contains the key that the load
      balancer will use to decrypt server IDs on QUIC packets.  See
      Section 7 to understand why sending keys in plaintext may be a
      safe strategy.

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4.4.6.  SERVER_ID Message

   A load balancer uses the SERVER_ID message (type=0x05) to exchange
   explicit server IDs.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    SIDL (8)   |       Server ID (variable)    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Load balancers send the SERVER_ID message when all global values for
   Stream or Block CIDs are sent out-of-band, so that only the server-
   unique values must be sent in-band.  The fields are identical to
   their counterparts in the Section 4.4.4 payload.

4.4.7.  MODULUS Message

   A load balancer uses the MODULUS message (type=0x06) to exchange just
   the modulus used in the plaintext CID algorithm.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Modulus (16)        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                            Token (64)                         +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Load balancers send the MODULUS when all global values for Plaintext
   CIDs are sent out-of-band, so that only the server-unique values must
   be sent in-band.  The Modulus field is identical to its counterpart
   in the ROUTING_INFO message.

5.  Config Rotation

   The first two bits of any connection-ID MUST encode the configuration
   phase of that ID.  QUIC-LB messages indicate the phase of the
   algorithm and parameters that they encode.

   A new configuration may change one or more parameters of the old
   configuration, or change the algorithm used.

   It is possible for servers to have mutually exclusive sets of
   supported algorithms, or for a transition from one algorithm to
   another to result in Fail Payloads.  The four states encoded in these

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   two bits allow two mutually exclusive server pools to coexist, and
   for each of them to transition to a new set of parameters.

   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.

   Servers MUST NOT generate new connection IDs using an old
   configuration when it has sent an Ack payload for a new
   configuration.

   Load balancers SHOULD NOT use a codepoint to represent a new
   configuration until it takes precautions to make sure that all
   connections using IDs with an old configuration at that codepoint
   have closed or transitioned.  They MAY drop connection IDs with the
   old configuration after a reasonable interval to accelerate this
   process.

5.1.  Configuration Failover

   If a server is configured to expect QUIC-LB messages, and it has not
   received these, it MUST generate connection IDs with the config
   rotation bits set to '0b11' and MUST use the "disable_migration"
   transport parameter in all new QUIC connections.  It MUST NOT send
   NEW_CONNECTION_ID frames with new values.

   A load balancer that sees a connection ID with config rotation bits
   set to '0b11' MUST revert to 5-tuple routing.

6.  Configuration Requirements

   QUIC-LB strives to minimize the configuration load to enable, as much
   as possible, a "plug-and-play" model.  However, there are some
   configuration requirements based on algorithm and protocol choices
   above.

   There are three levels of configuration that correspond to increasing
   levels of concern about the security of the load balancer-server
   path.

   The complete information requirements are described in Section 4.
   Load balancers MUST have configuration for all parameters of each
   routing algorithm they support.

   If there is any in-band communication, servers MUST be explicitly
   configured with the token of the load balancer they expect to

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   interface with.  Endpoints that use Stream Cipher CIDs MUST have this
   token regardless of the configuration method.

   Optionally, servers MAY be configured with the global parameters of
   supported routing algorithms.  This allows load balancers to use
   Server ID and Modulus Payloads, limiting the information sent in-
   band.

   Finally, servers MAY be directly configured with their unique server
   IDs or modulus, eliminating need for in-band messaging at all.  In
   this case, servers and load balancers MUST enable only one routing
   algorithm, as there is no explicit message to agree on one or the
   other.

7.  Security Considerations

   QUIC-LB is intended to preserve routability and prevent linkability.
   Attacks on the protocol would compromise at least one of these
   objectives.

   A routability attack would inject QUIC-LB messages so that load
   balancers incorrectly route QUIC connections.

   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.

7.1.  Outside attackers

   For an outside attacker to break routability, it must inject packets
   that correctly guess the 64-bit token, and servers must be reachable
   from these outside hosts.  Load balancers SHOULD drop QUIC-LB packets
   that arrive on its external interface.

   Off-path outside attackers cannot observe connection IDs, and will
   therefore struggle to link them.

   On-path outside attackers might try to link connection IDs to the
   same QUIC connection.  The Encrypted CID algorithm provides robust
   entropy to making any sort of linkage.  The Plaintext CID obscures
   the mapping and prevents trivial brute-force attacks to determine the
   routing parameters, but does not provide robust protection against
   sophisticated attacks.

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7.2.  Inside Attackers

   As described above, on-path inside attackers 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.

   On-path inside attackers can break routability for new and migrating
   connections by copying the token from QUIC-LB messages.  From this
   privileged position, however, there are many other attacks that can
   break QUIC connections to the server during the handshake.

   Off-path inside attackers cannot observe connection IDs to link them.
   To successfully break routability, they must correctly guess the
   token.

8.  IANA Considerations

   There are no IANA requirements.

9.  References

9.1.  Normative References

   [QUIC-TRANSPORT]
              Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", draft-ietf-quic-
              transport-16 (work in progress).

9.2.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

Appendix A.  Acknowledgments

Appendix B.  Change Log

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

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B.1.  Since draft-duke-quic-load-balancers-02

   o  Added Config Rotation

   o  Added failover mode

   o  Tweaks to existing CID algorithms

   o  Added Block Cipher CID algorithm

   o  Reformatted QUIC-LB packets

B.2.  Since draft-duke-quic-load-balancers-01

   o  Complete rewrite

   o  Supports multiple security levels

   o  Lightweight messages

B.3.  Since draft-duke-quic-load-balancers-00

   o  Converted to markdown

   o  Added variable length connection IDs

Author's Address

   Martin Duke
   F5 Networks, Inc.

   Email: martin.h.duke@gmail.com

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