Subject: DHCP Causing Routing Problem
To: None <tech-net@NetBSD.ORG>
From: Curt Sampson <>
List: tech-net
Date: 02/04/1998 22:21:13
I've got a couple of machines at home, an alpha, my router, running
NetBSD-1.3, and a sparc, my workstation, runing NetBSD-1.3. The
sparc has just one Ethernet interface on my home LAN.

The alpha has three interfaces: ep0 on my LAN, ep1, which is attached
to an ADSL modem via a crossover cable, and ppp0, which is a
dedicated modem connection to my ISP. My home LAN has its own class
C which is routed through the ISP and modem. I'm using ipf to block
incoming packets from ppp0 on the NFS and portmapper ports.

Now when the alpha comes up, only ep0 and ppp0 are brought up.
Everything works fine, and the sparc can access the net quite

If I remove my default route and then do a `dhclient ep1' on the
alpha, the interface comes up with an address, /etc/resolv.conf
gets fixed up, and a default route is added:

  default            link#1             UC          0        0      -  ep0 =>
  default            [adsl-router-ip]   UGS         3       71      -  ep1

This is the first thing I can't figure out. What's this ep0 default
route and where did it come from?

And now here's the thing that's even more odd. I was intending to
use NAT to translate my LAN address for the sparc into the ADSL
interface address, so the sparc could get to the world through
ADSL. However, at this point, whether or not I put in the NAT stuff,
the alpha doesn't route any more; instead it replies itself to all
packets from the sparc! For example, if I telnet or ftp from the
sparc to, I actually get a connection to the
alpha instead. Downing and deleting the ip address on ep1 and
restoring the routing table makes no difference; only rebooting
the machine seems to fix this condition.

Anyone have any clues as to what's going on here?


Curt Sampson	   Info at
Internet Portal Services, Inc.	   Through infinite mist, software reverberates
Vancouver, BC  (604) 257-9400	   In code possess'd of invisible folly.