http://sourceforge.net/projects/tftpterminal/files/Extras/SNMP%20WALKER.zip/download
The above is a SNMP walker, if you know the routing table you should be able to get the oids.
1.3.6.1.2.1.4.21.1. 1.129.44.25.0.0 172.25.0.0 < my network address
1.3.6.1.2.1.4.21.1.11.129.44.25.0.0 255.255.255.0 <my subnet mask
it looks like the oids might be dependant on the ip of the network address.
Greg