Reference Guide

Border Gateway Protocol IPv4 (BGPv4) | 183
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. It can also be set 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.
Dell Networking OS 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
MBGP for IPv4 Multicast is supported on the S5000 platform.
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.
Implementing BGP with 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 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 Dell Networking OS 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.
Advertising 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.
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.