Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 173
Next Hop, Multiprotocol BGP, Implement BGP, Additional Path (Add-Path) Support
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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. Implement BGP The following sections describe how BGP is implemented on the switch. Additional Path (Add-Path) Support The add-path feature reduces convergence times by advertising multiple paths to its peers for the same address prefix without replacing existing paths with new ones. By default, a BGP speaker advertises only the best path to its peers for a given address prefix. 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 also helps switchover to the next new best path when the current best path is unavailable. Border Gateway Protocol IPv4 (BGPv4) 173
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