Cisco Implementing and Operating Cisco Service Provider Network Core Technologies (350-501 SPCOR) 350-501 Question # 10 Topic 2 Discussion
350-501 Exam Topic 2 Question 10 Discussion:
Question #: 10
Topic #: 2
While implementing TTL security, an engineer issues the PE(config-router-af)#neighbor 2.2.2.2 ttl-security hops 2 command. After issuing this command, which BGP packets does the PE accept?
The ttl-security hops command sets the maximum number of hops that a BGP message can traverse. In this case, setting ttl-security hops 2 means that the router will accept BGP packets from a neighbor (2.2.2.2) only if the TTL is 253 or more. This is because the default TTL value is 255, and for each hop, the TTL is decremented by 1. Therefore, a packet from a directly connected neighbor would have a TTL of 254 when it reaches the PE router. If the packet has traversed one more router (making it two hops away), the TTL would be 253 upon arrival.
References: This information is based on the TTL security mechanism described in the Implementing and Operating Cisco Service Provider Network Core Technologies (SPCOR) training materials,
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