Gre tunnel pdf

Configuring GRE Tunnel By R P Porwal

Configuring a GRE tunnel involves creating a tunnel interface, which is a logical

interface. Then you must configure the tunnel endpoints for the tunnel interface.

To configure the tunnel source and destination, issue the tunnel source {ip-address |

interface-type} and tunnel destination {host-name | ip-address} commands under the

interface configuration mode for the tunnel.

The below example explain about how to create simple GRE tunnels between

endpoints and the necessary steps to create and verify the GRE tunnel between the two

networks.R1's and R2's Internal subnets(192.168.1.0/24 and 192.168.2.0/24) are

communicating with each other using GRE tunnel over internet.Both Tunnel interfaces

are part of the 172.16.1.0/24 network.

First step is to create our tunnel interface on R1 and R2

R1 R2

R1(config)# interface Tunnel1

R1(config-if)# ip address 172.16.1.1

255.255.255.0

R1(config-if)# ip mtu 1400

R1(config-if)# ip tcp adjust-mss 1360

R1(config-if)# tunnel source 1.1.1.1

R1(config-if)# tunnel destination 2.2.2.2



255.255.255.0




R2(config-if)# tunnel destination

1.1.1.1

Since GRE is an encapsulating protocol, we adjust the maximum transfer unit (mtu) to

1400 bytes and maximum segment size (mss) to 1360 bytes. Because most transport

MTUs are 1500 bytes and we have an added overhead because of GRE, we must

reduce the MTU to account for the extra overhead. A setting of 1400 is a common

practice and will ensure unnecessary packet fragmentation is kept to a minimum.

After configuring tunnel,two tunnel endpoints can see each other can verify using an

icmp echo from one end.

R1# ping 172.16.1.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.16.1.2, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms

Workstations on either network will still not be able to reach the other side unless a

routing is configure on each router.Here We will configure static route on both router.

R1(config)# ip route 192.168.2.0 255.255.255.0 172.16.1.2

R2(config)# ip route 192.168.1.0 255.255.255.0 172.16.1.1

Now both networks (192.168.1.0/24 and 192.168.2.0/24) are able to freely

communicate with each other over the GRE Tunnel .

First step is to create our tunnel interface on R1 and R2 :

R1 R2



255.255.255.0







255.255.255.0





Since GRE is an encapsulating protocol, we adjust the maximum transfer unit (mtu) to

1400 bytes and maximum segment size (mss) to 1360 bytes. Because most transport

MTUs are 1500 bytes and we have an added overhead because of GRE, we must

reduce the MTU to account for the extra overhead. A setting of 1400 is a common

practice and will ensure unnecessary packet fragmentation is kept to a minimum.

After configuring tunnel,two tunnel endpoints can see each other can verify using an

icmp echo from one end.

R1# ping 172.16.1.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.16.1.2, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms

Workstations on either network will still not be able to reach the other side unless a

routing is configure on each router.Here We will configure static route on both router.

R1(config)# ip route 192.168.2.0 255.255.255.0 172.16.1.2

R2(config)# ip route 192.168.1.0 255.255.255.0 172.16.1.1

Now both networks (192.168.1.0/24 and 192.168.2.0/24) are able to freely

communicate with each other over the GRE Tunnel .

Gre tunnel pdf

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