To configure a GRE tunnel (modify accordingly):
! interface Tunnel0 ip address 192.168.0.1 255.255.255.0 tunnel source Ethernet0/0 tunnel destination 1.0.0.2 ! interface Ethernet0/0 ip address 1.0.0.1 255.255.255.0 ! router ospf 1 network 192.168.0.0 0.0.0.255 area 0 !
To verify a GRE tunnel:
Router#show ip int bri Interface IP-Address OK? Method Status Protocol Ethernet0/0 1.0.0.2 YES manual up up Ethernet0/1 unassigned YES unset administratively down down Ethernet0/2 unassigned YES unset administratively down down Ethernet0/3 unassigned YES unset administratively down down Serial1/0 unassigned YES unset administratively down down Serial1/1 unassigned YES unset administratively down down Serial1/2 unassigned YES unset administratively down down Serial1/3 unassigned YES unset administratively down down Tunnel0 192.168.0.2 YES manual up up Router#show int tunnel 0 Tunnel0 is up, line protocol is up Hardware is Tunnel Internet address is 192.168.0.2/24 MTU 17916 bytes, BW 100 Kbit/sec, DLY 50000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation TUNNEL, loopback not set Keepalive not set Tunnel linestate evaluation up Tunnel source 1.0.0.2 (Ethernet0/0), destination 1.0.0.1 Tunnel Subblocks: src-track: Tunnel0 source tracking subblock associated with Ethernet0/0 Set of tunnels with source Ethernet0/0, 1 member (includes iterators), on interface Tunnel protocol/transport GRE/IP Key disabled, sequencing disabled Checksumming of packets disabled Tunnel TTL 255, Fast tunneling enabled Tunnel transport MTU 1476 bytes Tunnel transmit bandwidth 8000 (kbps) Tunnel receive bandwidth 8000 (kbps) Last input 00:00:09, output 00:00:09, output hang never Last clearing of "show interface" counters 00:02:40 Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0 Queueing strategy: fifo Output queue: 0/0 (size/max) 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 13 packets input, 1296 bytes, 0 no buffer Received 0 broadcasts (0 IP multicasts) 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 16 packets output, 1636 bytes, 0 underruns 0 output errors, 0 collisions, 0 interface resets 0 unknown protocol drops 0 output buffer failures, 0 output buffers swapped out Router#show ip route 192.168.0.0 Routing entry for 192.168.0.0/24, 2 known subnets Attached (2 connections) Variably subnetted with 2 masks C 192.168.0.0/24 is directly connected, Tunnel0 L 192.168.0.2/32 is directly connected, Tunnel0 Router#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 192.168.0.1 0 FULL/ - 00:00:31 192.168.0.1 Tunnel0
