Administrator Guide

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 trac 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 dened in IETF RFC 2858. MBGP allows dierent 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 dierent from the unicast routing topology.
NOTE: It is possible to congure 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.
Implement BGP with the Dell Networking OS
The following sections describe how to implement BGP on the Dell Networking OS.
Additional Path (Add-Path) Support
The add-path feature reduces convergence times by advertising multiple paths to its peers for the same address prex without
replacing existing paths with new ones. By default, a BGP speaker advertises only the best path to its peers for a given address
prex. If the best path becomes unavailable, the BGP speaker withdraws its path from its local RIB and recalculates a new best path.
This situation requires both IGP and BGP convergence and can be a lengthy process.
BGP add-path reduces the time taken for BGP convergence by advertising multiple paths to its peers for the same address prex
without new paths implicitly replacing the existing paths. An iBGP speaker that receives multiple paths from its peers should
calculate the best path in its own. BGP add-path helps switchover to next new best path based on IGP convergence time when best
path becomes unavailable.
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Border Gateway Protocol IPv4 (BGPv4)