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AS Path
The AS path is the list of all ASs that all the prefixes listed in the update have passed through.
The local AS number is added by the BGP speaker when advertising to a eBGP neighbor.
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
Dell#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 traffic to another BGP speaker, rather than
waiting for a speaker to advertise.
The system allows you to set the next hop attribute in the CLI. Setting the next hop attribute lets you
determine a router as the next hop for a BGP neighbor.
Multiprotocol BGP
Multiprotocol extensions for BGP (MBGP) is defined in IETF RFC 2858. MBGP allows different types of
address families to be distributed in parallel.
MBGP allows information about the topology of the IP multicast-capable routers to be exchanged
separately from the topology of normal IPv4 and IPv6 unicast routers. It allows a multicast routing
topology different from the unicast routing topology.
NOTE: It is possible to configure BGP peers that exchange both unicast and multicast network layer
reachability information (NLRI), but you cannot connect multiprotocol BGP with BGP. Therefore,
you cannot redistribute multiprotocol BGP routes into BGP.
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Border Gateway Protocol IPv4 (BGPv4)