Debian 3.0/kernel 2.4.18 ARP "reflection?"

Sorry for the verbose message. This might be something obvious, but none
of my searches seem to return things that apply.

First, my equipment/network. I have a box running Debian 3.0 kernel
2.4.18-1-k6 #2 installed from the debian package. I have another box
running FreeBSD 5.1. These are behind a Netgear RP614 router/firewall.

I just upgraded the FreeBSD box from 4.7 to 5.1 for unrelated reasons,
but it existed under both releases. I had previously installed SuSE on
the linux box until a few months ago, and hadn't had these problems under
SuSE.

Neither box has any trouble seeing the router or the outside world. The
linux box has no trouble connecting to the FreeBSD box via various
protocols (ssh,NFS,ping, etc.).

When I do an NFS mount from the linux box ("thishere") to the FreeBSD box
("poobrain"), the request seems to go through fine. "poobrain" shows the
mount in its /var/db/mountdtab file. A df on "thishere" shows that
poobrain:/usr is mounted except... it has actually just re-mounted its
own /usr on that mount point. If I do 'ssh poobrain' from "thishere" I
connect, log in, except I've connected to thishere.

Any connections from "poobrain" to "thishere" just time out. "rpcinfo -p
thishere" gets "rpcinfo: can't contact portmapper: RPC: Remote system error -
Operation timed out"

On the linux box:
1. I added "192.168.0.2 poobrain" to the linux box's /etc/hosts.
2. I added "ALL : 192.168.0.2" to the linux box's /etc/hosts.allow
3. rpcinfo -p shows I have portmapper, nlockmgr, status, nfs, and mountd
all listening for both tcp and udp protocols. Additionally, both NFS v2
and v3 are available.
4. The proper entries are in /etc/exports

The FreeBSD is properly configured on its end as an NFS server and
client.

The FreeBSD box normally picks up the MAC address for the linux box, or I
can set it manually with arp -s. The linux box doesn't seem to pick up
the FreeBSD box, although it does get the MAC addr from the router.
However, if I try 'arp -s 192.168.0.2 <MAC addr>' on the linux box I get
"SIOCSARP: Invalid argument".

ethereal run on the linux box shows that it is receiving the RPC calls
from FreeBSD but it doesn't respond. I don't see anything obvious in the
logs.

Also, I tried booting the FreeBSD into WinXP, and it is also "ignored" by
the linux box.


Thanks for any help...
-K