TTL of BGP Packet Expires
By default, an eBGP peering occurs between directly connected routers. This means the routers forming the eBGP peering are expected to be within one router hop of each other. With an iBGP peering, the routers can be up to 255 router hops from each other and still form a peering. Example 18-14 shows the output of show bgp ipv4 unicast neighbors | include BGP neighbor|TTL, which displays that the eBGP neighbor at 10.1.12.1 must be reachable in 1 router hop, and the iBGP neighbor at 5.5.5.5 can be up to 255 hops away. If the neighbor is not reachable in the number of hops listed, the BGP packet expires, and no neighbor relationship is formed.
Example 18-14 Verifying the TTLs of eBGP and iBGP Packets
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