OSPF Generalized TTL Security (GTSM)

• Provides an additional security mechanism by ensuring that the neighboring OSPF is exactly the same number of hops away as in the configuration.

• When an OSPF router receives a message from another OSPF neighbor, it compares the TTL in IP header with the TTL that is configured for that neighbor.

Rx(config)#router ospf 10

Rx(config-router)#ttl-security all-interfaces

OR

R1(config)#interface se1/0

R1(config-if)#ip ospf ttl-security

Note: You have to configure GTSM on all neighbor routers.