Path: utzoo!attcan!uunet!gohp3!dc
From: dc@gohp3.graphon.com (Darren Croke)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: TCP segment size -- user defined?
Message-ID: <538@gohp3.graphon.com>
Date: 8 Oct 90 23:35:11 GMT
References: <266@aldetec.oz.au> <256@ubeaut.oz.au>
Reply-To: dc@graphon.com (Darren Croke)
Organization: GraphOn Corp., San Jose, CA.
Lines: 24

In article <256@ubeaut.oz.au> mwp@ubeaut.oz.au (Michael Paddon) writes:
>
> text deleted
>
>There is not much point setting TCP_MSS to be greater than
>	(maximum IP packet size - IP header size - TCP header size)
>[536 octets] since IP fragmentation will take place. Receipt of a
>fragmented packet is an all or nothing proposition; a good thing to
>avoid for throughput reasons.
>

The 536 octects in brackets is the minimum but by no means always 
equal to (maximum IP packet size - IP header size - TCP header size).

Look at the packets on an Ethernet sometime. I am running a 4.3 BSD
TCP/IP implementation here that quite happily negotiates a MSS of 
1000 bytes and then proceeds to send unfragmented 1000 byte packets.

I think you will find that it is common for IP implementations to
send and accept datagrams without fragmentation up to 
(connected network MTU - IP header size - TCP header size).

Darren Croke.
dc@graphon.com