Re: Asymmetric CIDs
Eric Rescorla <ekr@rtfm.com> Fri, 16 February 2018 18:39 UTC
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From: Eric Rescorla <ekr@rtfm.com>
Date: Fri, 16 Feb 2018 10:38:55 -0800
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Subject: Re: Asymmetric CIDs
To: Martin Duke <martin.h.duke@gmail.com>
Cc: Ian Swett <ianswett@google.com>, IETF QUIC WG <quic@ietf.org>
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On Fri, Feb 16, 2018 at 9:52 AM, Martin Duke <martin.h.duke@gmail.com> wrote: > Thanks for writing this up, ekr. This incorporates many of the suggestions > I made in objection to this project (perhaps coincidentally) and I like it > a lot. > > Advantages of this: > - In the common case where most of the data is server->client, clients can > get away with shorter Conn IDs to reduce overhead. > - Omit-conn-id just becomes a case where length = 0. Does this sidestep > some of Google's transition issues? > - If a client sends NEW_CONNECTION_ID, that indicates an intention to > migrate, and is a good cue for the server to send the same. We should add a > SHOULD to specify this behavior. > > I must be missing something, however, regarding implicit CIDs. > > If there's a NAT rebinding, how is the server supposed to extract the CID? > The assumption is that the server either: (a) always uses the same CID length (b) has a structured CID which starts with the length. But that we don't need to mandate which one in the protoocl > Furthermore, this obviates the entire concept of using Connection ID for > routing; it's not obviously a savings to store CID length in a table vs. > just storing the destination server. > I don't think you hae to do this, but maybe I am confused. See above and tell me if you think I'm wrong -Ekr > Lastly, if we encode the length somewhere that seems to solve the > Stateless Reset issue. > > > On Fri, Feb 16, 2018 at 9:25 AM, Ian Swett <ianswett@google.com> wrote: > >> Thanks for the excellent summary EKR. I like this design and think the >> breakage of stateless reset in certain cases is acceptable, since it only >> applies if both sides must have their preferred connection ID present in >> order to route correctly, which is a use case that's impossible in the >> status quo. I have not come up with any other downsides. >> >> On Fri, Feb 16, 2018 at 12:01 PM, Eric Rescorla <ekr@rtfm.com> wrote: >> >>> Hi folks, >>> >>> After a bunch of discussion, the CID task force came down to rough >>> consensus that asymmetric conn IDs were probably the right >>> direction (CID task force members, please feel free to voice dissent >>> here). Here's a complete writeup of what I think would be needed >>> for asymmetric connection IDs. It's not a PR, because I think >>> something self-contained is cleaner. >>> >>> Note that if we adopt this direction, we would be sacrificing >>> public reset under some conditions (see previous emails to the >>> list) and we would need to decide if it was worth keeping at all. >>> >>> >>> OVERVIEW >>> The basic idea is that each side gets to dictate the connection IDs >>> that are used to send to it. During the handshake, you establish those >>> CIDs and then each side can issue new CIDs during the connection. The >>> main advantage of this is that it allows for symmetric topologies in >>> which >>> the client is also behind some kind of stateless LB/router rather than >>> just the server. See Issue #1091 for more info on this. >>> >>> >>> The overall handshake looks something like this: >>> >>> Client Server >>> >>> Initial [CID=XXX] {recv-CID=YYY} ----------------> >>> <-------------- Cleartext [CID=YYY] {recv-CID=ZZZ} >>> Cleartext [CID=ZZZ], {recv-CID=YYY} -------------> >>> <-------------------------- Short header [CID=YYY] >>> Short header [CID=ZZZ] --------------------------> >>> >>> >>> The client's initial CID (XXX) is special, and either consists of >>> >>> (a) a randomly chosen dummy CID. Proposal: require this to be >>> 8 bytes or at least a minimum. This should be the same >>> for all Initial packets in a connection (unless a stateless >>> reject is received, as below). >>> (b) a CID which it received from the server in a stateless reject >>> >>> All the server's packets are sent with the client's receive CID (YYY) >>> and all subsequent client packets are sent with the server's receive >>> CID (ZZZ). The general rule is that you should send with the >>> connection ID that you most recently received (where recently >>> is defined as highest PN). >>> >>> Note: I believe it's safe to just use the sending CID as the mixin >>> for the KDF, but I haven't thought this entirely through yet. >>> >>> Finally, you can send NEW_CONNECTION_ID in either direction to provide >>> a new connection ID for the other side to use. The general assumption >>> is that you can do this at any time, just as with current QUIC, and >>> that any time you send to a new remote 3-tuple you should change CIDs >>> if you can. Note that this means that endpoints should try to make >>> sure that the other side has spare CIDs in case they need to migrate. >>> >>> >>> WIRE ENCODING >>> As we discussed in the meeting the short header should just have >>> an implicit length CID. This gives us the following short header: >>> >>> +-+-+-+-+-+-+-+-+ >>> |0|C|K| Type (5)| >>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ >>> | | >>> + [Connection ID (*)] + <- >>> change from 64 >>> | | >>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ >>> | Packet Number (8/16/32) ... >>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ >>> | Protected Payload (*) ... >>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ >>> >>> Note that we may also be able to dispense with the C bit, if each >>> side just gets to say "send me this CID exactly", why do we want >>> to say "here is my CID but you can omit it". >>> >>> >>> We have several options about the long header. The first question >>> is where recv-CIDs go. In previous versions I suggested putting >>> them in transport parameters, or elsewhere in the TLS handshake, >>> and that might still be viable, though it has some drawbacks [0], >>> so the other alternative is to put both CIDs in in the long header. >>> This would look something like: >>> >>> +-+-+-+-+-+-+-+-+ >>> |1| Type (7) | >>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ >>> | DCID-Length | | >>> +-+-+-+-+-+-+-+-+ Dst Connection ID (*) + >>> | | >>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ >>> | SCID-Length | | >>> +-+-+-+-+-+-+-+-+ Src Connection ID (*) + >>> | | >>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ >>> | Version (32) | >>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ >>> | Packet Number (32) | >>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ >>> | Payload (*) ... >>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ >>> >>> The semantics here are that the first value is the CID you want to >>> send to and the second one is the value you want used to send to you >>> (I've inverted these to keep the order the same as short header). >>> >>> Two notes about this encoding: >>> >>> 1. I think we agreed that we didn't want arbitrary length CIDs up to >>> 255 bytes, and yet we have room in this length byte. I propose we >>> limit it to 31 bytes and then grease the remaining 3 bits [1]. >>> >>> 2. Because the client sends its CID first, there's no way to get the >>> current QUIC semantics of the server just dictates the CID. I propose >>> we fix that by defining a special sentinel CID (all 1s, all 0s, >>> whatever) of whatever our maximum length is that means "just use your >>> own CID". >>> >>> We can endlessly bikeshed on this structure. >>> >>> >>> Finally, we will need to update NEW_CONNECTION_ID to allow a variable >>> length CID. This would look like this: >>> >>> 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 >>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ >>> | Sequence (i) ... >>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ >>> | CID-Length | | >>> +-+-+-+-+-+-+-+-+ Connection ID (*) + >>> | | >>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ >>> | | >>> + + >>> | | >>> + Stateless Reset Token (128) + >>> | | >>> + + >>> | | >>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ >>> >>> >>> >>> [0] However, in the transport parameters design, if the server's >>> handshake gets reordered, the client might need to send some ACKs with >>> the initial CID. However, we've agreed that the client's IP address >>> has to be stable, so this isn't a problem. Alternately, you could >>> change C->S CIDs in the short header if that was easier. >>> >>> [1] An alternative would be to have a sparse range (e.g., you can >>> express 0-7 and then 8-22 by 2s, assuming I have counted correctly) >>> and then we could pack both lengths into a single byte. As I said, >>> lots of opportunities for bikeshedding here. >>> >>> >> >
- Asymmetric CIDs Eric Rescorla
- Re: Asymmetric CIDs Ian Swett
- RE: Asymmetric CIDs Lubashev, Igor
- Re: Asymmetric CIDs Ted Hardie
- Re: Asymmetric CIDs Martin Duke
- Re: Asymmetric CIDs Christian Huitema
- Re: Asymmetric CIDs Roberto Peon
- Re: Asymmetric CIDs Eric Rescorla
- Re: Asymmetric CIDs Martin Duke
- Re: Asymmetric CIDs Eric Rescorla
- Re: Asymmetric CIDs Christian Huitema
- RE: Asymmetric CIDs Nick Banks
- Re: Asymmetric CIDs Ian Swett
- Re: Asymmetric CIDs Roberto Peon
- Re: Asymmetric CIDs Mikkel Fahnøe Jørgensen
- Re: Asymmetric CIDs Christian Huitema
- Re: Asymmetric CIDs Martin Thomson
- Re: Asymmetric CIDs Mikkel Fahnøe Jørgensen
- Re: Asymmetric CIDs Kazuho Oku