Dell Force10 S4820T S4820T Configuration Guide - Page 191

Multiprotocol BGP MBGP for IPv6 unicast is supported on platforms e c MBGP for IPv4 Multicast is supported on platform c e s Multiprotocol Extensions for BGP (MBGP) is defined in IETF RFC 2858. MBGP allows different types of address families to be distributed in parallel. This allows information about the topology of 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. Implementing BGP with FTOS 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 requires both IGP and BGP convergence and can therefore be a lengthy process. BGP add-path on FTOS reduces the time taken for BGP convergence by advertising multiple paths to its peers for the same address prefix 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. Advertise IGP cost as MED for redistributed routes When using multipath connectivity to an external AS, you can advertise the MED value selectively to each peer for redistributed routes. For some peers you can set the internal/IGP cost as the MED while setting others to a constant pre-defined metric as MED value. FTOS 8.3.1.0 and later support configuring the set metric-type internal command in a route-map to advertise the IGP cost as the MED to outbound EBGP peers when redistributing routes. The configured set metric value overwrites the default IGP cost. By using the redistribute command in conjunction with the route-map command, you can specify whether a peer advertises the standard MED or uses the IGP cost as the MED. Border Gateway Protocol IPv4 (BGPv4) | 191