What is the default IP time-to-live (TTL) value for an EBGP session?

• A. 1
• B. 63
• C. 128
• D. 255

Answer: (A)

The default IP time-to-live (TTL) value for an EBGP session is 255. TTL is a field in the IP header that indicates how many hops a packet can traverse before it is discarded.

In the case of EBGP (External Border Gateway Protocol), the TTL value is critical because EBGP sessions typically occur between routers that may not be directly connected. The higher the TTL value, the more hops a packet can make without being dropped. By default, EBGP uses a TTL of 255 to ensure that packets can travel across multiple networks.

Values like 1, 63, and 128 are not standard defaults for EBGP, as they would limit the scope considerably, potentially dropping packets if they traverse more than the allowed hops. A TTL of 1 would only allow packets to be sent to directly connected neighbors, which contradicts the purpose of EBGP, as it is designed for external connections.