Re: Increasing QUIC connection ID size

Roberto Peon <fenix@fb.com> Fri, 12 January 2018 00:45 UTC

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From: Roberto Peon <fenix@fb.com>
To: Victor Vasiliev <vasilvv@google.com>, IETF QUIC WG <quic@ietf.org>
Subject: Re: Increasing QUIC connection ID size
Thread-Topic: Increasing QUIC connection ID size
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Date: Fri, 12 Jan 2018 00:45:16 +0000
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Having the server specify the connID-size as part of the connection setup+version negotiation would certainly be grease-y.

A larger connID helps to solve a lot of L4<->L7 routing issues, agreed, pre-supposing that the server always picks the new/alternate conn-ID for the client.
-=R

From: QUIC <quic-bounces@ietf.org> on behalf of Victor Vasiliev <vasilvv@google.com>
Date: Thursday, January 11, 2018 at 3:16 PM
To: IETF QUIC WG <quic@ietf.org>
Subject: Increasing QUIC connection ID size

Hi everyone,

In the current version of QUIC, the connection ID size is fixed to be a 64-bit opaque blob, and that is set as an invariant in the protocol.

I’ve looked into possibility of using a connection ID to encode the specific server details into it (to provide stability of the connection in case of load balancing changes, especially BGP flaps for anycast IPs), and have chatted about this with other people I knew were interested in this.  It seems like 64 bits might be too small for this purpose, and we might want to leave an opportunity to extend the connection ID size.

The basic idea is that you want to be able to:

  1.  Store some routing metadata in the connection ID.
  2.  Have some entropy that allows distinguish users with identical routing metadata.
  3.  Have a checksum to ensure the validity of routing information
  4.  Encrypt the information above to prevent disclosing the route information and allow generating uncorrelatable connection IDs.
There are two underlying issues here.  The first problem is that all of this does not fit well into 64 bits, and you have to seriously compromise on the strength of the checksum (which is bad especially if you want it to be a MAC rather than a checksum).  The second problem is that encrypting 64-bit values fast is actually fairly hard since the block ciphers easily available in hardware have 128-bit block size, and the performance requirements on load balancers are tighter than on servers.

In other words, having a 128-bit connection ID provides for an easy secure way to generate unlinkable connection IDs on migration.

So, the problem we’re trying to solve is that the connection ID is too small.  There are two questions I believe the working group should answer at this point:

  1.  Do we want to address this problem at this point in standardization process?
  2.  If we don’t address this problem right now, how do we structure the standard in a way that we can extend the connection ID in the future?
There are multiple ways to solve the problem of making connection ID larger.  One is to just add extra bit to the “omit connection ID” field to allow 128-bit connection IDs.  Another approach is to allow connection ID size to be explicitly specified by the server, and then assume that the load balancer knows that size and no one else on the path needs to read it.

There’s also a question of how much of connection IDs do middleboxes (excluding load balancers and other boxes owned by the same entity as either client or server) need to know.  We could go for both “middleboxes should be always able to read the entire ID” and “middleboxes should not read connection IDs at all options”, but I think there’s also a room for more flexible formulations like “middleboxes always get first 64 bits and they have useful entropy to distinguish connections”.

  -- Victor.