The two PCs on subnet 10.1.1.0/24 can communicate with each over via layer 2. This is possible because of the L2TP configuration on the routers. The routers are not, and do not need to be, on the same layer 2 subnet as the PCs. The fourth router, R4, was added to demonstrate an alternative path that can be used via OSPF.
PC1> show ip NAME : PC1[1] IP/MASK : 10.1.1.10/24 GATEWAY : 0.0.0.0
PC2> show ip NAME : PC2[1] IP/MASK : 10.1.1.20/24 GATEWAY : 0.0.0.0
! pseudowire-class pctest1 encapsulation l2tpv3 protocol none ip local interface FastEthernet1/0 ! pseudowire-class pctest2 encapsulation l2tpv3 protocol none ip local interface FastEthernet2/0 ! interface Loopback1 ip address 172.31.0.1 255.255.255.255 ! interface FastEthernet0/0 no ip address duplex auto speed auto no cdp enable xconnect 192.168.21.3 2 encapsulation l2tpv3 manual pw-class pctest2 l2tp id 11 22 ! interface FastEthernet1/0 ip address 192.168.10.1 255.255.255.0 duplex auto speed auto ! interface FastEthernet2/0 ip address 192.168.11.1 255.255.255.0 duplex auto speed auto ! router ospf 10 log-adjacency-changes network 172.31.0.0 0.0.0.255 area 0 network 192.168.10.0 0.0.0.255 area 0 network 192.168.11.0 0.0.0.255 area 0 !
! pseudowire-class pctest1 encapsulation l2tpv3 protocol none ip local interface FastEthernet1/0 ! pseudowire-class pctest2 encapsulation l2tpv3 protocol none ip local interface FastEthernet2/0 ! interface Loopback1 ip address 172.31.0.3 255.255.255.255 ! interface FastEthernet0/0 no ip address duplex auto speed auto no cdp enable xconnect 192.168.11.1 2 encapsulation l2tpv3 manual pw-class pctest2 l2tp id 22 11 ! interface FastEthernet1/0 ip address 192.168.20.3 255.255.255.0 duplex auto speed auto ! interface FastEthernet2/0 ip address 192.168.21.3 255.255.255.0 duplex auto speed auto ! router ospf 10 log-adjacency-changes network 172.31.0.0 0.0.0.255 area 0 network 192.168.20.0 0.0.0.255 area 0 network 192.168.21.0 0.0.0.255 area 0 !
! interface Loopback1 ip address 172.31.0.2 255.255.255.255 ! interface FastEthernet0/0 ip address 192.168.10.2 255.255.255.0 duplex auto speed auto ! interface FastEthernet1/0 ip address 192.168.20.2 255.255.255.0 duplex auto speed auto ! router ospf 10 log-adjacency-changes network 172.31.0.0 0.0.0.255 area 0 network 192.168.10.0 0.0.0.255 area 0 network 192.168.20.0 0.0.0.255 area 0 !
! interface Loopback1 ip address 172.31.0.4 255.255.255.255 ! interface FastEthernet0/0 ip address 192.168.11.2 255.255.255.0 duplex auto speed auto ! interface FastEthernet1/0 ip address 192.168.21.2 255.255.255.0 duplex auto speed auto ! router ospf 10 log-adjacency-changes network 172.31.0.0 0.0.0.255 area 0 network 192.168.11.0 0.0.0.255 area 0 network 192.168.21.0 0.0.0.255 area 0 !
O 192.168.10.0/24 [110/11] via 192.168.20.2, 00:19:29, FastEthernet1/0 172.31.0.0/32 is subnetted, 4 subnets C 172.31.0.3 is directly connected, Loopback1 O 172.31.0.2 [110/2] via 192.168.20.2, 00:19:29, FastEthernet1/0 O 172.31.0.1 [110/12] via 192.168.21.2, 00:19:29, FastEthernet2/0 [110/12] via 192.168.20.2, 00:19:29, FastEthernet1/0 O 172.31.0.4 [110/2] via 192.168.21.2, 00:19:29, FastEthernet2/0 O 192.168.11.0/24 [110/11] via 192.168.21.2, 00:19:30, FastEthernet2/0 C 192.168.21.0/24 is directly connected, FastEthernet2/0 C 192.168.20.0/24 is directly connected, FastEthernet1/0
O 192.168.10.0/24 [110/11] via 192.168.20.2, 00:19:29, FastEthernet1/0 172.31.0.0/32 is subnetted, 4 subnets C 172.31.0.3 is directly connected, Loopback1 O 172.31.0.2 [110/2] via 192.168.20.2, 00:19:29, FastEthernet1/0 O 172.31.0.1 [110/12] via 192.168.21.2, 00:19:29, FastEthernet2/0 [110/12] via 192.168.20.2, 00:19:29, FastEthernet1/0 O 172.31.0.4 [110/2] via 192.168.21.2, 00:19:29, FastEthernet2/0 O 192.168.11.0/24 [110/11] via 192.168.21.2, 00:19:30, FastEthernet2/0 C 192.168.21.0/24 is directly connected, FastEthernet2/0 C 192.168.20.0/24 is directly connected, FastEthernet1/0
C 192.168.10.0/24 is directly connected, FastEthernet0/0 172.31.0.0/32 is subnetted, 4 subnets O 172.31.0.3 [110/2] via 192.168.20.3, 00:18:57, FastEthernet1/0 C 172.31.0.2 is directly connected, Loopback1 O 172.31.0.1 [110/11] via 192.168.10.1, 00:18:57, FastEthernet0/0 O 172.31.0.4 [110/3] via 192.168.20.3, 00:18:57, FastEthernet1/0 O 192.168.11.0/24 [110/11] via 192.168.10.1, 00:18:57, FastEthernet0/0 O 192.168.21.0/24 [110/2] via 192.168.20.3, 00:18:57, FastEthernet1/0 C 192.168.20.0/24 is directly connected, FastEthernet1/0
O 192.168.10.0/24 [110/11] via 192.168.11.1, 00:18:19, FastEthernet0/0 172.31.0.0/32 is subnetted, 4 subnets O 172.31.0.3 [110/2] via 192.168.21.3, 00:18:19, FastEthernet1/0 O 172.31.0.2 [110/3] via 192.168.21.3, 00:18:19, FastEthernet1/0 O 172.31.0.1 [110/11] via 192.168.11.1, 00:18:19, FastEthernet0/0 C 172.31.0.4 is directly connected, Loopback1 C 192.168.11.0/24 is directly connected, FastEthernet0/0 C 192.168.21.0/24 is directly connected, FastEthernet1/0 O 192.168.20.0/24 [110/2] via 192.168.21.3, 00:18:20, FastEthernet1/0