Running NetBSD 1.6 on i386 hardware.  Ethernet card is a 3com 3c595.

I am unable to make outbound connections from one of my NetBSD machines
to my gateway (external DSL modem).  I can ping other machines on my
netblock, but pings externally receive a host is down response.

The gateway is set correctly, and inbound connections (ie ssh and
inbound web connections) work fine, and I am able to ping other machines
on my local network just fine.

The arp table indicates that arp lookops are failing.  arp -a says:

soggy1.drizzle.com (216.162.199.1) at (incomplete) on ep0
soggy110.drizzle.com (216.162.199.110) at 00:a0:24:cf:27:de on ep0
jeff.hell.org (216.162.199.114) at 00:a0:24:cf:27:de on ep0
binky.hell.org (216.162.199.117) at 00:a0:24:51:3b:6a on ep0

It's the first entry that connects to my ISP, where the ethernet address
is listed as incomplete.

Other machines on the network (including one that is more-or-less
identically) have no problem connecting outbound, and arp -a gives the
proper entry to the DSL modem.  As part of trying to locaet a fault in
my physical network, I have replaced the ethernet card and the ethernet
cable (in a moment of desperation) and plugged it into another port in
the hub, and I powered down the hub, DSL modem and computer
simultaneously, and none of this helped.  Briefly after rebooting at one
point, arp -a returned the proper ethernet address of the DSL modem, but
after a few network pings, the entry returned to incomplete.

Ideas on how to resolve this?

-m