Concept Guide

AS Path
The AS path is the list of all ASs that all the prexes listed in the update have passed through.
The local AS number is added by the BGP speaker when advertising to a eBGP neighbor.
NOTE: Any update that contains the AS path number 0 is valid.
The AS path is shown in the following example. The origin attribute is shown following the AS path information (shown in bold).
Example of Viewing AS Paths
DellEMC#show ip bgp paths
Total 30655 Paths
Address Hash Refcount Metric Path
0x4014154 0 3 18508 701 3549 19421 i
0x4013914 0 3 18508 701 7018 14990 i
0x5166d6c 0 3 18508 209 4637 1221 9249 9249 i
0x5e62df4 0 2 18508 701 17302 i
0x3a1814c 0 26 18508 209 22291 i
0x567ea9c 0 75 18508 209 3356 2529 i
0x6cc1294 0 2 18508 209 1239 19265 i
0x6cc18d4 0 1 18508 701 2914 4713 17935 i
0x5982e44 0 162 18508 209 i
0x67d4a14 0 2 18508 701 19878 ?
0x559972c 0 31 18508 209 18756 i
0x59cd3b4 0 2 18508 209 7018 15227 i
0x7128114 0 10 18508 209 3356 13845 i
0x536a914 0 3 18508 209 701 6347 7781 i
0x2ffe884 0 1 18508 701 3561 9116 21350 i
Next Hop
The next hop is the IP address used to reach the advertising router.
For EBGP neighbors, the next-hop address is the IP address of the connection between the neighbors. For IBGP, the EBGP next-hop
address is carried into the local AS. A next hop attribute is set when a BGP speaker advertises itself to another BGP speaker outside its
local AS and when advertising routes within an AS. The next hop attribute also serves as a way to direct trac to another BGP speaker,
rather than waiting for a speaker to advertise. When a next-hop BGP neighbor is unreachable, then the connection to that BGP neighbor
goes down after hold down timer expiry. The connection ap can also be obtained immediately with Fallover enabled. BGP routes that
contain the next-hop as the neighbor address are not sent to the neighbor. You can enable this feature using the neighbor sender-
side-loopdetect command.
NOTE
: For EBGP neighbors, the next-hop address corresponding to a BGP route is not resolved if the next-hop address is not
the same as the neighbor IP address.
NOTE: The connection between a router and its next-hop BGP neighbor terminates immediately only if the router has received
routes from the BGP neighbor in the past.
184 Border Gateway Protocol (BGP)