



QUIC                                                         M. Munizaga
Internet-Draft                                       Ethereum Foundation
Intended status: Standards Track                              M. Seemann
Expires: 3 September 2026                                      Smallstep
                                                            2 March 2026


                 QUIC Alternative Server Address Frames
           draft-munizaga-quic-alternative-server-address-00

Abstract

   This document specifies an extension to QUIC to allow a server to
   advertise alternative addresses.

About This Document

   This note is to be removed before publishing as an RFC.

   The latest revision of this draft can be found at
   https://marcopolo.github.io/alternative-server-address/draft-
   munizaga-quic-alternative-server-address.html.  Status information
   for this document may be found at https://datatracker.ietf.org/doc/
   draft-munizaga-quic-alternative-server-address/.

   Discussion of this document takes place on the QUIC Working Group
   mailing list (mailto:quic@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/quic/.  Subscribe at
   https://www.ietf.org/mailman/listinfo/quic/.

   Source for this draft and an issue tracker can be found at
   https://github.com/MarcoPolo/alternative-server-address.

Status of This Memo

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

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

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




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   This Internet-Draft will expire on 3 September 2026.

Copyright Notice

   Copyright (c) 2026 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/
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Negotiating Extension Use . . . . . . . . . . . . . . . . . .   3
   5.  Server initiated Paths  . . . . . . . . . . . . . . . . . . .   4
   6.  Alternative Address Frames  . . . . . . . . . . . . . . . . .   4
   7.  Frame properties  . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Interaction with the Multipath Extension for QUIC . . . . . .   5
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
     9.1.  Request Forgery Attacks . . . . . . . . . . . . . . . . .   5
     9.2.  DDoS - Thundering herd  . . . . . . . . . . . . . . . . .   5
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
     10.1.  QUIC Transport Parameter . . . . . . . . . . . . . . . .   6
     10.2.  QUIC Frame Types . . . . . . . . . . . . . . . . . . . .   6
   11. Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   6
   Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   The QUIC transport protocol allows a client to migrate connections at
   any time to any new address (Section 9 of [QUIC-TRANSPORT]).  This
   allows the connection to survive changes to the client's address.  A
   client can use this mechanism to keep redundant paths available or
   transparently move to a different local address.  A server, in
   contrast, can not use alternative addresses as redundant paths and
   has no way to dynamically signal a preferred address.  In some
   deployments, specifically peer to peer settings, adding this symmetry
   is useful.



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   This document specifies an extension to QUIC that allows a server to
   inform a client of alternative, possibly preferred, addresses.

2.  Conventions and Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Motivation

   In peer to peer networks, the role of server and client is arbitrary.
   An endpoint may serve as a client in one connection and a server in
   another.  A peer acting as a server would like to communicate to its
   peer its alternative addresses.  The server peer does this for both
   redundancy (a peer may advertise a globally reachable relayed unicast
   address as a backup) and to signal preference (a peer may be using a
   proxy, and wish to migrate to a new proxy).

   While it is not the primary goal, this extension may also assist in
   NAT traversal by migrating to a dynamically chosen server address.  A
   server could have a client connect over a relay, and later migrate to
   a direct connection after applying NAT traversal techniques.  The
   specific NAT traversal techniques are out of scope of this document.

   TODO: Is the above NAT paragraph useful?  Would it be better to leave
   this implied?

4.  Negotiating Extension Use

   alternative_address (0xff0969d85c):

   Clients advertise their support of this extension by sending the
   alternative_address (0xff0969d85c) transport parameter (Section 7.4
   of [QUIC-TRANSPORT]) with an empty value.  Sending this transport
   parameter signals to the server that the client understands the
   ALTERNATIVE_V4_ADDRESS and ALTERNATIVE_V6_ADDRESS frames.

   Servers MUST NOT send this transport parameter.  A client that
   supports this extension and receives this transport parameter MUST
   abort the connection with a TRANSPORT_PARAMETER_ERROR.

   Endpoints MUST NOT remember the value of this extension for 0-RTT.






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5.  Server initiated Paths

   In connections that use this extension, clients MUST NOT discard
   probing packets received from an unknown server address.  Clients
   MUST validate the path per Section 9.1 of [QUIC-TRANSPORT].

   TODO alternatively, should clients treat a server address identified
   by an alternative address frame as known, and accept probing packets
   from this address?  This would require the server to know its address
   before hand, which could be annoying if the server is behind a NAT
   and initially reached over a relay.

6.  Alternative Address Frames

   A server uses the following frames to inform the client of an
   alternative address.  The Preferred bit signals this address is
   preferred over the currently in-use server address.  The Retire bit
   signals that this address is no longer an alternative address for
   this server (TODO what happens if the server sends a Retire bit on
   the current address?).  Clients SHOULD close paths associated with
   addresses for which the Retire bit is set.

   When the Retire bit is not set, clients SHOULD open a path to the
   provided address.  If the Preferred bit is set, clients should
   migrate to or otherwise prioritze the path with the provided address.

   The alternative address frames are defined as follows:

   ALTERNATIVE_V4_ADDRESS Frame {
     Type (i) = 0x1d5845e2,
     Preferred (1),
     Retire (1),
     unused (6)
     Status Sequence Number (i),
     IPv4 Address (32),
     IPv4 Port (16),
   }

   ALTERNATIVE_V6_ADDRESS Frame {
     Type (i) = 0x1d5845e3,
     Preferred (1),
     Retire (1),
     unused (6)
     Status Sequence Number (i),
     IPv6 Address (128),
     IPv6 Port (16),
   }




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   Following the common frame format described in Section 12.4 of
   [QUIC-TRANSPORT].

   The sequence number space is common to the two frame types, and
   monotonically increasing values MUST be used when sending updates for
   a given IP and Port tuple.

   TODO: Do we want a probing frame that identifies this path as
   preferred so it can be used to signal a request to migrate to this
   path?  Do we want to reuse PATH_STATUS_BACKUP or
   PATH_STATUS_AVAILABLE to harmonize with the Multipath QUIC extension?

7.  Frame properties

   all frames are ack-eliciting, and MUST only be sent in the
   application data packet number space.

   The server SHOULD ensure that its peer has a sufficient number of
   available and unused connection IDs, as the client will be unable to
   probe paths without an unused connection ID.  The server MAY bundle a
   NEW_CONNECTION_ID frame with a alternative address frame.  Likewise,
   the client should ensure the same to allow the server to probe new
   paths.

8.  Interaction with the Multipath Extension for QUIC

   This extension compliments the Multipath extension for QUIC by
   allowing the server to contribute more information to the client for
   alternative paths.

9.  Security Considerations

9.1.  Request Forgery Attacks

   The same considerations from Section 21.5 of [QUIC-TRANSPORT] apply
   here as well.

9.2.  DDoS - Thundering herd

   A malicious server could wait until it has received a large number of
   clients, and request a migration from all of them at the same time to
   a victim endpoint.  If the clients all migrate at the same time, they
   may overload or otherwise negatively impact the victim endpoint.

   Clients may mitigate this by randomly delaying the migration.

10.  IANA Considerations




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10.1.  QUIC Transport Parameter

   This document registers the alternative_address transport parameter
   in the "QUIC Transport Parameters" registry established in
   Section 22.3 of [QUIC-TRANSPORT].  The following fields are
   registered:

   Value:  0xff0969d85c

   Parameter Name:  alternative_address

   Status:  Provisional

   Specification:  This document

   Change Controller:  IETF (iesg@ietf.org)

   Contact:  Marco Munizaga (marco@marcopolo.io)

10.2.  QUIC Frame Types

   TODO

11.  Normative References

   [QUIC-TRANSPORT]
              Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,
              <https://www.rfc-editor.org/rfc/rfc9000>.

   [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/rfc/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

Acknowledgments

   TODO acknowledge.

Questions

   *  Any new security considerations from allowing a dynamically chosen
      preferred address?



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Authors' Addresses

   Marco Munizaga
   Ethereum Foundation
   Email: marco@marcopolo.io


   Marten Seemann
   Smallstep
   Email: martenseemann@gmail.com









































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