Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!OAC.UCLA.EDU!CSYSMAS
From: CSYSMAS@OAC.UCLA.EDU (Michael Stein)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: What Size IP on TR?
Message-ID: <9006300011.AA06801@ucbvax.Berkeley.EDU>
Date: 29 Jun 90 22:41:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 22

> >What size of packets will vendor x's tcp/ip over token ring tend to
> >send out onto the wire?.....
>
> At one point, there seemed to be a general consensus of the IBM
> implementations that the length indicated in the RIF was to be 2052
> bytes (in fact, some of them insisted on it).  This may have
> changed, but people who coded to suit it may not have.

Watch out!  What the RIF says and what you really want to do may
be different things.

An example is a RIF which says 2052 where there are routers to
Ethernet (max IP packet size of 1500).  Any IP packet larger than
1500 will get fragmented.

Using a RIF size of 1500 (then next smaller than 2052) is worse
but for the other direction.  A 1500 byte RIF size only allows
1500-8 => 1492 bytes of IP packet (8 bytes are used for the IEEE
stuff on TR, but not on Ethernet) and will result in full size
Ethernet packets being fragmented on Token Ring.

PS: Some Token Ring support is leaning toward 4 to 8 K packets...