Subject: LDP formats

From: "Grant, Scott" <[email-masked]>
Date: Mon, 7 May 2001 12:34:09 -0700

I'm working on a decode for sniffer and I've encountered something that
isn't exactly described in RFC 3036. I have a trace file from Extreme
Networks where there are frames with several PDUs in a single TCP message.
I've read through RFC 3036, and I can't find anything saying that there can
or can't be multiple PDUs in a frame. Is this something that will become a
defacto standard due to several vendors doing this? I'd appreciate any
comments.

Scott Grant

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From: Bob Thomas <[email-masked]>
Date: Mon, 07 May 2001 16:03:40 -0400

> defacto standard due to several vendors doing this? I'd appreciate any

The trace is legal.  Note also that it is legal for a single LDP PDU to
span multiple TCP segments.

RFC3036 specifies the use of TCP to transport messages for LDP sessions.
IMO it is neither necessary nor desirable for it to specify the mapping
of data (LDP messages) to TCP segments.

Bob

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From: Jack Brennen <[email-masked]>
Date: Mon, 07 May 2001 16:10:26 -0400

> defacto standard due to several vendors doing this? I'd appreciate any

I think that the answer here is that there is no such thing as a "single
TCP message" -- TCP is a stream-based protocol; there are no internal
boundaries defined at the transport layer.  The only boundaries in an
LDP session stream are the boundaries between PDUs.  At the application
level, an LDP implementation must be prepared to parse PDUs whether they
arrive in huge blocks of 10 PDUs at once, or whether they arrive 1 byte
at a time -- either can happen over TCP.

  Jack

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From: David Charlap <[email-masked]>
Date: Mon, 07 May 2001 16:17:55 -0400

Bob Thomas wrote:
> 
> IMO it is neither necessary nor desirable for it to specify the
> mapping of data (LDP messages) to TCP segments.

Nor is it necessarily possible.

-- David