Question : 1721 vlan

how do we setup vlans on the fastethernet 0 interface of a 1721 cisco router.

Answer : 1721 vlan

Several 12.3 versions - about 15 in all that are listed

Keeping the same feature set that you have:

IP/ADSL/FW/IDS PLUS IPSEC 3DES

Here is a sampling:

12.3(11)YZ
c1700-k9o3sy7-mz.12.3-11.YZ
12.3(8)YG4
c1700-k9o3sy7-mz.12.3-8.YG4
12.3(7)XR6
c1700-k9o3sy7-mz.12.3-7.XR6
12.3(4)XK4
c1700-k9o3sy7-mz.12.3-4.XK4