Explanation/Reference:
Explanation:
neighbor ip-address ttl-security hops hop-count
ExamplE.
Router(config-router)# neighbor 10.1.1.1 ttl-security hops 2 Configures the maximum number of hops that separate two peers. The hop-count argument is set to number of hops that separate the local and remote peer. If the

expected TTL value in the IP packet header is 254, then the number 1 should be configured for the hop- count argument. The range of values is a number from 1 to 254. When this feature is enabled, BGP will accept incoming IP packets with a TTL value that is equal to

or greater than the expected TTL value. Packets that are not accepted are silently discarded. The example configuration sets the expected incoming TTL value to at least 253, which is 255 minus

the TTL value of 2, and this is the minimum TTL value expected from the BGP peer. The local router will accept the peering session from the 10.1.1.1 neighbor only if it is 1 or 2 hops away.
ReferencE. http://www.cisco.com/c/en/us/td/docs/ios/12_2s/feature/guide/fs_btsh.html