Subject: [tcpm] draft-bonica and TCP segmentation

From: "Caitlin Bestler" <[email-masked]>
Date: Thu, 23 Mar 2006 11:07:38 -0800

>   Whenever TCP generates a segment, it searches the key-chain for an
>   active key.  Section 6 of this document describes TCPs active key
>   selection criteria.

Doesn't this imply that *only* the original sender can do TCP
segmentation? I believe the precedent recently reaffirmed for
MPA (RDDP WG) was that a protocl MUST NOT assume that the
sender's segmetnation would be preserved by the network.

If message boundaries are lost, a valid network occurrence,
how could you interpret the content?

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From: Joe Touch <[email-masked]>
Date: Thu, 23 Mar 2006 11:15:57 -0800

Caitlin Bestler wrote:
> segmentation?

That's already part of the TCP spec - TCP is defined only between the
TCP endpoints; there are no provisions for in-network resegmentation,
which would affect ACK clocking, Nagle, etc.

> I believe the precedent recently reaffirmed for

Segmentation at the TCP layer must be preserved, or it's not TCP.
Network layer re-'segmentation' is a network protocol issue, e.g., it is
supported in IPv4 but not in IPv6.

Other transport protocols can make other decisions. TCP could be proxied
- i.e., terminated by an intermediate node and resegmented there - but a
'transparent' proxy that does so violates TCP.

Further, we're talking about authenticated segments; resegmentation
without resigning the message with the appropriate key is basically just
an attack - one that fails.

> how could you interpret the content?

Can you clarify what you mean by 'message'? If you're talking about a
message boundary within TCP, the application must place it there. TCP
does not preserve application data units.

Joe

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From: John Heffner <[email-masked]>
Date: Thu, 23 Mar 2006 14:37:50 -0500

> sender's segmetnation would be preserved by the network.

That's contrary to my understanding.  I just scanned over 
draft-ietf-rddp-mpa-02, and didn't see anything relating to this.  Can you 
provide some more detail?

  -John