Table of Contents
Configure a GRE tunnel via the Internet. This creates a virtual point-to-point connection between the two locations.
Configure a GRE tunnel between R11 and R21 in the following network diagram. the GRE tunnel provides a virtual point-to-point connection between R11 and R21.
To configure the GRE tunnel interface, it is assumed that communication is available between R11 and R21.
Configuring and Verifying the GRE Tunnel Interface
Configuring GRE Tunnel Interface
Create a tunnel interface with R11 and R21. You can use any interface number, in this case 0. You can use the tunnel destination and tunnel source commands to specify the destination and source IP addresses of the IP headers for forwarding. You also need the IP address to send and receive IP packets on Tunnel0. Instead of configuring the IP address explicitly, we configure ip unnumbered to use the IP address of Loopback0.
interface Tunnel0 ip unnumbered Loopback0 tunnel source Ethernet0/0 tunnel destination 22.214.171.124
interface Tunnel0 ip unnumbered Loopback0 tunnel source Ethernet0/0 tunnel destination 126.96.36.199
Verifying GRE Tunnel Interface
The show interface tunnel0 command verifies the tunnel interface between R11 and R21. the output of show interface tunnel0 at R11 is as follows.
R11#show interfaces tunnel 0 Tunnel0 is up, line protocol is up Hardware is Tunnel Interface is unnumbered. Using address of Loopback0 (10.1.0.11) MTU 1514 bytes, BW 9 Kbit/sec, DLY 500000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation TUNNEL, loopback not set Keepalive not set Tunnel source 188.8.131.52 (Ethernet0/0), destination 184.108.40.206 Tunnel protocol/transport GRE/IP Key disabled, sequencing disabled Checksumming of packets disabled Tunnel TTL 255 Fast tunneling enabled Tunnel transmit bandwidth 8000 (kbps) Tunnel receive bandwidth 8000 (kbps) -- omitted --
Enable RIP on tunnel interface
Configure routing with RIP so that communication between Site1 and Site2 is possible via the GRE tunnel.
router rip network 10.0.0.0 version 2 no auto-summary
The GRE tunnel is ip unnumbered and has the same IP address as Loopback0. Therefore, if RIP is enabled on Loopback0, RIP will be enabled on tunnel0 at the same time.
RIP is enabled in the GRE tunnel, and we are able to learn the route information of each other’s sites via the GRE tunnel. the routing status in R11 is as follows
R11#show ip protocols Routing Protocol is "rip" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Sending updates every 30 seconds, next due in 20 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Redistributing: rip Default version control: send version 2, receive version 2 Interface Send Recv Triggered RIP Key-chain Ethernet0/1 2 2 Loopback0 2 2 Tunnel0 2 2 Automatic network summarization is not in effect Maximum path: 4 Routing for Networks: 10.0.0.0 Routing Information Sources: Gateway Distance Last Update 10.1.12.12 120 00:00:01 10.2.0.21 120 00:00:27 Distance: (default is 120) R11#show ip route ～省略～ Gateway of last resort is 220.127.116.11 to network 0.0.0.0 18.104.22.168/24 is subnetted, 1 subnets C 22.214.171.124 is directly connected, Ethernet0/0 10.0.0.0/8 is variably subnetted, 8 subnets, 2 masks R 10.2.12.0/24 [120/1] via 10.2.0.21, 00:00:03, Tunnel0 C 10.1.12.0/24 is directly connected, Ethernet0/1 R 10.1.0.12/32 [120/1] via 10.1.12.12, 00:00:05, Ethernet0/1 R 10.2.1.0/24 [120/2] via 10.2.0.21, 00:00:03, Tunnel0 R 10.1.1.0/24 [120/1] via 10.1.12.12, 00:00:05, Ethernet0/1 C 10.1.0.0/24 is directly connected, Loopback0 R 10.2.0.21/32 [120/1] via 10.2.0.21, 00:00:04, Tunnel0 R 10.2.0.22/32 [120/2] via 10.2.0.21, 00:00:04, Tunnel0 S* 0.0.0.0/0 [1/0] via 126.96.36.199
Verifying communication between sites
Verify the communication between PC1 and PC2. Execute a ping from PC1 to PC2.
PC1> ping 10.2.1.100 84 bytes from 10.2.1.100 icmp_seq=1 ttl=60 time=103.327 ms 84 bytes from 10.2.1.100 icmp_seq=2 ttl=60 time=89.114 ms 84 bytes from 10.2.1.100 icmp_seq=3 ttl=60 time=78.018 ms 84 bytes from 10.2.1.100 icmp_seq=4 ttl=60 time=98.787 ms 84 bytes from 10.2.1.100 icmp_seq=5 ttl=60 time=102.156 ms
ICMP packets when pinging from PC1 to PC2 will be output from the tunnel0 interface on R11.
When output from the tunnel0 interface, a GRE header and a new IP header are added and output from E0/0. It will be routed to R21 with the new IP header.