Dell S6000-ON, Configuration Manual

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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.
MBGP uses either an IPv4 address configured on the interface (which is used to establish the IPv6
session) or a stable IPv4 address that is available in the box as the next-hop address. As a result, while
advertising an IPv6 network, exchange of IPv4 routes does not lead to martian next-hop message logs.
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 with Dell Networking OS
The following sections describe how to implement BGP on 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 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.
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.
Use 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 with the
route-map
command, you can specify whether a peer
advertises the standard MED or uses the IGP cost as the MED.
When configuring this functionality:
• If the
redistribute
command does not have
metric
configured and the BGP peer outbound
route-map does have
metric-type internal
configured, BGP advertises the IGP cost as MED.
• If the
redistribute
command has
metric
configured (
route-map set metric
or
redistribute route-type metric
) and the BGP peer outbound route-map has
metric-type
internal
configured, BGP advertises the metric configured in the
redistribute
command as
MED.
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Border Gateway Protocol IPv4 (BGPv4)