Re: ICMP's & IP src addrs


Tait Cyrus (hi.unm.edu!cyrus@hc.dspo.gov)
16 Sep 88 16:46:13 GMT


In article <303@wjh12.harvard.edu> > lotto@wjh12.UUCP (Jerry Lotto) writes:
>In article <21843@tut.cis.ohio-state.edu> karl@triceratops.cis.ohio-state.edu (Karl Kleinpaste) writes:
>>As long as I was at it, I decided to look at what a large collection
>>of diverse machines did with pings to .255. I hit our backbone...
>>Responding with 128.146.8.255:
>>Sun-3/180 (SunOS 3.5.1 [UNIX]).
>
>And I am sure that someones bridge will then decide that they know
>where "the broadcast address" lives and stop forwarding it.

If an IP bridge does this, then its' implementation of IP/TCP is
hosed.

The only time we have seen a problem simular to this is when a new
machine was installed and the person installing it mis-typed
and the machine thought it's IP address was broadcast. This
resulted in all machines sending broadcast packets to this machine.
We noticed this problem when all of our gateways lost all their
routes (routing packets were going to this screwed machine).
Simply pulling this machine off of the net solved the problems.

>I have seen this (anti-social) behavior in DEC Lanbridges and it
>does not bode well for the network until someone resets the beast.
>Takes a while to find if you aren't looking for it.

Huhhh???? A DEC Lanbridge is protocol independent. I think what you
are refering to is the fact that a DEC Lanbridge (using old proms)
will not forward packets sending to the broadcast address
(ff:ff:ff:ff:ff:ff) iff it has seen this address in the src field
of some other ethernet/802.3 packet. We have seen this happen and
the result is NO broadcasts get forwarded through the DEC Lanbridge;
i.e. RWHO/ROUTE/etc packets are NOT seen by machines on the other
side of the DEC Lanbridge.

We have yet to find the machine that thinks its' hardware address
is ff:ff:ff:ff:ff:ff, though we are getting new DEC Lanbridge prom
that take care of this problem.

>--
>Gerald Lotto - Harvard Chemistry Dept.

Tait Cyrus
University of New Mexico
Dept. Electrical and Computer Engineering
Parallel Processig Research Group
cyrus@hi.unm.edu



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