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RE: Clarification needed

2002-12-02 03:12:40
Hi All,

Anything behind these numbers "64 and 128" as specified in RFC 1144 [page

" Each slot must be large enough to hold a maximum length TCP/IP header 128
{ The maximum header length, fixed by the protocol design, is 64
bytes of IP and 64 bytes of TCP} "


 -----Original Message-----
From:   owner-ietf(_at_)ietf(_dot_)org [mailto:owner-ietf(_at_)ietf(_dot_)org]  
On Behalf Of
Sent:   Monday, 2 December 2002 1:59 PM
To:     ramanad(_at_)FUTURE(_dot_)FUTSOFT(_dot_)COM
Cc:     ietf(_at_)ietf(_dot_)org
Subject:        Re: Clarification needed

 << File: ATT00013.dat >> On Mon, 02 Dec 2002 10:18:22 +0530, Ramana Divvi
<ramanad(_at_)future(_dot_)futsoft(_dot_)com>  said:

IHL              ------>  IHL is the Total IPv4 header length, maximum is
( 15x4 = 60 bytes) ----refer RFC 791
DataOffset   ------>  DataOffset is total TCP header size ( in simple
, maximum is 15 ( 15x4 = 60 bytes) ----refer RFC 793
From above two, combined TCP/IP header maximum length is 120 bytes.


But in RFC 1144 (page 13) , it was defined as 128 bytes. Is it correct? If
so please clarify the same.

No.  You need a 128 octet buffer *for the compressed header*. The hint is
"since the output packet can be larger than the input packet".  Contemplate
algorithm, and see if you can see what states will cause the 120 byte header
require 128 bytes after "compression".

                                Valdis Kletnieks
                                Computer Systems Senior Engineer
                                Virginia Tech

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