What is the maximum number of hops from the device that generated the given output
to its BGP neighbor at 4.4.4.4?
Refer to the exhibit.
A.
3
B.
252
C.
5
D.
255
E.
2
F.
254
Explanation:
same as example:
https://supportforums.cisco.com/document/86776/securing-ebgp-sessions-ttl-securityfeature
the missing part from output is (so that is the answer)
External BGP neighbor may be up to 3 hops away.
command applied on that appliance is:
neighbor 4.4.4.4 ttl-security hops 3This feature is configured using neighbor <ip-address> ttl-security hops <count> BGP
configuration command. The TTL value is calculated by the router from the configured
hop count i.e. TTL = 255 – (hop count).
This feature has few limitations
On enabling neighbor ttl-security feature, neighbor ebgp-multihop is not required.
The feature is only for EBGP and not IBGP.
4.4.4.4 is originating BGP packets with a TTL of 255, and R expects the packets it receives from 4.4.4.4 to have at least 252 (as in BGP configuration of R has neighbor
4.4.4.4 ttl-security hops 3, so a TTL value 255-3=252).
The BGP will establish and maintain the session only if the TTL value in the IP packet is
equal to or greater than the TTL value configured for the peer.