Routera:s0/1:172.16.1.1
eo/0:192.168.2.1
Routerb:s0/1:172.16.1.2
e0/0:192.168.3.1
Routerc:so/1:172.16.2.1
e0/0:192.168.2.2
Routerd:s0/1:172.16.2.2
e0/0:192.168.3.2
---
ip route 192.168.2.0 255.255.255.0 172.16.1.1
ip route 172.16.2.0 255.255.255.0 192.168.3.2
no ip route 192.168.2.0 255.255.255.0 172.16.1.1
no ip route 172.16.2.0 255.255.255.0 192.168.3.2
---
router rip
network 192.168.3.0
network 172.16.0.0
router rip
no network 192.168.3.0
no network 172.16.0.0
---
ip route 0.0.0.0 0.0.0.0 192.168.3.0 255.255.255.0
no ip route 0.0.0.0 0.0.0.0 192.168.3.0 255.255.255.0
---
router igrp 5
network 192.168.3.0
network 172.16.0.0
---
access-list 1 deny 172.16.2.0 0.0.0.255
access-list 1 permit any
s0/1
ip access-group 1 out
access-list 102 deny tcp 172.16.2.0 0.0.0.255 192.168.3.0 0.0.0.255 eq 25
access-list 102 permit ip any any
e0/0
ip access-group 102 in
---