NFS through firewall

[James Pifer]

Hi. I have a server in our DMZ and I'm exporting a specific directory
with NFS. I have an internal server that I want to mount it on. The
internal server is allowed through the firewall without restriction.
Firewall guy tells me it's wide open for this internal server, TCP and
UDP. 

When I try to mount the drive I get this error:
pmap_getmaps rpc problem: RPC: Unable to receive; errno = Connection
reset by peer

On the server running NFS I get this:
rpc.mountd: authenticated mount request from [internal_server]:680
for /usr/test (/usr/test)

If I do an nmap from the internal server to the external server running
I get:

(The 1648 ports scanned but not shown below are in state: closed)
PORT      STATE SERVICE
22/tcp    open  ssh
80/tcp    open  http
111/tcp   open  rpcbind
443/tcp   open  https
933/tcp   open  unknown
5001/tcp  open  commplex-link
5801/tcp  open  vnc-http-1
5901/tcp  open  vnc-1
10000/tcp open  snet-sensor-mgmt

A UDP port scan seems to hang. 

If I do an rpcinfo on the external server running NFS I get:
# rpcinfo -p 127.0.0.1
   program vers proto   port
    100000    2   tcp    111  portmapper
    100000    2   udp    111  portmapper
    100024    1   udp  32768  status
    100024    1   tcp  32768  status
    391002    2   tcp  32769  sgi_fam
    100011    1   udp    930  rquotad
    100011    2   udp    930  rquotad
    100011    1   tcp    933  rquotad
    100011    2   tcp    933  rquotad
    100003    2   udp   2049  nfs
    100003    3   udp   2049  nfs
    100021    1   udp  32781  nlockmgr
    100021    3   udp  32781  nlockmgr
    100021    4   udp  32781  nlockmgr
    100005    1   udp  32782  mountd
    100005    1   tcp  59483  mountd
    100005    2   udp  32782  mountd
    100005    2   tcp  59483  mountd
    100005    3   udp  32782  mountd
    100005    3   tcp  59483  mountd

Any thoughts on what the problem is?

Thanks,
James