problem using ports other than 161/162

[Daniel G. <dg...@ed...>]

For years we've used some linux monitoring software (mrtg) to connect to 
snmpd on machines within our own network.
It has worked great, but now we want to monitor that location from 
another place, and our ISP blocks SNMP traffic.
When they say they block SNMP traffic I'm guessing, and have tested via 
nmap, that they are actually just blocking port 161 and 162.

So, I'd like to change the port that my servers are listening on, but 
I'm missing something in the way that SNMP works, because I can't 
connect remotely even though I've made the following changes:

/etc/snmp/snmpd.conf:
agentaddress udp:10161

/etc/snmp/snmptrapd.conf:
snmpTrapdAddr 10162

Restarting snmpd and snmptrapd shows that I'm now listening on ports 
10161 and 10162 udp:
netstat -nau
udp        0      0 0.0.0.0:10161               0.0.0.0:*
udp        0      0 0.0.0.0:10162               0.0.0.0:*

I can snmpwalk locally:
snmpwalk -Os -c public -v 1 localhost sysName
sysName.0 = STRING: mymachine.com

This also works and gives same info:
snmpwalk -Os -c public -v 1 localhost:10161 system
sysName.0 = STRING: mymachine.com


But, I still can't snmp walk from the remote network...
snmpwalk -Os -c public -v 1 MY_REMOTE_IP:10161 system
Timeout: No Response from MY_REMOTE_IP:10161

...although nmap shows that the ports are open:
nmap -sU -p 10161,10162 mymachine.com
Starting Nmap 4.11 ( http://www.insecure.org/nmap/ ) at 2008-09-03 18:03 CDT
Interesting ports on mymachine.com (Some_IP_WAS_HERE):
PORT      STATE         SERVICE
10161/udp open|filtered unknown
10162/udp open|filtered unknown


For good measure, I also changed /etc/services from 161/162 to 
10161/10162 on the snmpd machine.

What am I lacking?

Thanks,
Daniel