James B. VanBokkelen (JBVB@AI.AI.MIT.EDU)
Fri, 24 Jul 87 23:32:20 EDT

    I heard an interesting rumor that the IBM distributed TCP/IP
    source routes all its packets.

    Is this possibly true????


What I have been told is this:

1. IBM's TCP/IP for the PC, as released for use on their Token Ring Adapter,
does not ARP in the conventional sense: Instead, it sends the ARP as an
"all rings" broadcast, with an empty Routing Information Field. When the
reply comes back, it looks for the filled-in RIF field, and uses it. No
RIF field, no function.

2. IBM's TCP/IP for AIX can behave as above, but only if you enable it
with some magic switch.

3. Other IBM TCP/IP products will try the "all rings" approach, but only
if they get no reply to a conventional ARP.

4. IBM bridges don't pass conventional (not "all rings") broadcasts.

So, yes, folks, source routing is alive & well at Yorktown, whether or not
ISO has accepted it. No official position is being stated here, but comments
I've heard range from "That's WRONG! Let's try to talk them into conforming."
to "Oh, hell, they won't listen, and they're going to sell piles of that
junk - It's gonna be a dirty job, but we'd better change the code..."

I've heard nothing about aberrant behavior on Ether, so apparently they're
only punishing their own pioneering customers at the moment....


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