Subject: kern/6472: ARP requests go out on all interfaces
To: None <>
From: Martin J. Laubach <>
List: netbsd-bugs
Date: 11/20/1998 17:42:30
>Number:         6472
>Category:       kern
>Synopsis:       ARP requests are sent on all interfaces
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people (Kernel Bug People)
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Nov 20 09:05:01 1998
>Originator:     Martin J. Laubach
>Release:        NetBSD 1.3.2
System: NetBSD asparagus 1.3.2 NetBSD 1.3.2 (ASPARAGUS) #14: Sat Aug 29 16:16:00 CEST 1998 mjl@asparagus:/home/temp/kernel/sys/arch/i386/compile/ASPARAGUS i386

  On a machine with multiple interfaces, arp requests go out on all
interfaces, not just the one the arp request is destined for.

  The problem is that some ADSL Modems (Pairgain) seem to answer arp
request for *everything* that is not in their net, I suppose to be nice
to braindead network configurations.

  IMO an arp request should only be sent on the interface the host sought
can possibly be connected to.

  Put two IF in a machine, for example fxp1 as and
fxp0 as

  Do a "tcpdump -i fxp0 arp", and then a "ping". See
arp requests going out on fxp0.

  (And if you got a pairgain adsl modem, see it answer with its own
MAC, overwriting the arp info from the real host!!)

  Send arp requests to relevant interface(s) only.