[comp.protocols.tcp-ip] TCP/IP and OSI over FDDI

jk@capone.UUCP (John Knight) (09/19/89)

Hi Netlanders:
         
My company is developing an FDDI controller and is interested in 
running several different protocol stacks simultaneously over the 
controller.  At a minimum, we'd like to run both TCP/IP and OSI.  
With our current implementation of Ethernet, it is possible to 
route the packets to the appropriate protocol stack (ie. TCP/IP or 
OSI) via the type/length field in the Ethernet frame header.
         
We would like to do the same type of thing with FDDI frames.  
Unfortunately, the X3T9.5 MAC soon-to-be standard does not tell 
how one might route packets to various different protocol stacks.
         
Does anyone know if there is a document that specifies how to 
route an FDDI frame to OSI or TCP/IP protocol stacks?  Even within 
TCP/IP there is a question on how to route ARP and RARP traffic.  
The main burning question is as follows: How can/does the FDDI 
software distinguish between traffic intended for OSI, IP, RARP, 
or ARP?
         
In advance, thanks for your help.
John Knight

Dave_Katz@UM.CC.UMICH.EDU (09/20/89)

>Does anyone know if there is a document that specifies how to
>route an FDDI frame to OSI or TCP/IP protocol stacks?  Even within
>TCP/IP there is a question on how to route ARP and RARP traffic.
>The main burning question is as follows: How can/does the FDDI
>software distinguish between traffic intended for OSI, IP, RARP,
>or ARP?
 
For TCP/IP, RFC 1103 proposes a method of framing ARP and IP
over FDDI using 802.2 LLC and SNAP headers (in which the
classic "ethertype" field is carried).  This document is only
a draft, but the fundamentals points aren't likely to change.
 
For OSI, there's no official document as to how Network Layer
protocols will be carried, although it's essentially a foregone
conclusion that 802.2 LLC will be used, with an LSAP value
of "OSI Network Layer Protocol."
 
So, to answer the question directly, the algorithm is something
like:
  If FDDI LLC frame
    [assume 802.2 LLC in use]
    if LSAP = SNAP
       determine protocol type based on SNAP type
    else if LSAP = OSI NL
       determine protocol type based on first octet of NL packet
    else
       ???
 
It appears likely that the SNAP format will be used for all
protocols that run with Ethernet framing, not just IP and ARP.
 
Protocol identification for OSI is done at the network layer; the
first octet of the packet determines which of several protocols
(CLNP, ES-IS, X.25, etc.) is in use.  An ISO Technical Report,
"Protocol Identification at the Network Layer," (the TR # escapes
me) spells this out.

CERF@A.ISI.EDU (09/24/89)

John,

I am extremely interested in multiprotocol methods -
please let me know what you turn up on FDDI.

Vint Cerf