> The system is a P90 running NetBSD/i386 1.4.1, with two ISA NE2000 cards
> (one for LAN, one for cable modem).
> 
> The problem is that it can't talk to the Internet through the new
> Terayon (8000029 revD) cable modem supplied by the ISP. It can, however,
> talk through a friend's slightly older cablemodem a LanCity (don't know
> model no). The friend subscribes to exactly the same service, and lives
> 2 blocks away. He is on a different (larger) IP subnet.

Did you set the default route correctly?  can you ping your first-hop
router?

Is the cablemodem system doing DHCP or did they give you a static
address?

> Specific observations:
> In the non-working situation, tcpdump shows ping packets passing out of
> ne0, and ping replies passing back in. It also shows ARP doing its job
> and correctly resolving the (remote) gateway's mac address. 

If you're seeing packets coming back, perhaps they're malformed in
some way.

Does "netstat -s -p ip" or "netstat -s -p icmp" show any "interesting"
counters incrementing?  (e.g., "bad header checksums", "bad length", ...).

if you do a tcpdump -i ne0 -s 1024 -x, are the returned icmp packets
malformed in any obvious way?

> Ping, however, reports 100% packet loss.

have you verified that this isn't a nameserver config issue (ping -n).

> The only thing we changed when trying it on the older cable modem was
> the IP address and netmask.. We simply typed "ifconfig ne0 $friends_ip
> netmask 255.255.254.0" on a fresh boot.

if the other user is on a different subnet, you presumably also need
to change (at a minimum) the default route.

					- Bill