Advertising Best Routes - Juniper BGP - CONFIGURATION GUIDE V 11.1.X Configuration Manual

JUNOSe 11.1.x BGP and MPLS Configuration Guide

Advertising Best Routes

By default, BGP selects from its routing table one best route to each destination. If
BGP learned that best route from an internal peer, then the BGP speaker does not
advertise a route to that destination to the speaker's internal peers.
In earlier software releases, the default behavior was for BGP to select two best routes
to any destination. The best route learned from external (including confederation)
peers was advertised to the speaker's internal peers. The best route learned from all
sources was advertised to the speaker's external peers.
You can issue the bgp advertise-external-to-internal command to cause BGP to
revert to advertising two potentially different routes to its peers. See "Selecting the
Best Path" on page 106 for information about the process BGP uses to determine best
routes.
bgp advertise-best-external-to-internal
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Advertising Routes
Use the backdoor keyword to lower the preference of an EBGP route to the
specified prefix by setting the administrative distance to that of an internal BGP
route, 200. Use this option to favor an IGP backdoor route over an EBGP route
to a specific network. BGP does not advertise the specified network. See
"Configuring Backdoor Routes" on page 139 for more information.
The next hop for the network is the next hop for the route contained in the
routing table.
This command takes effect immediately.
Use the no version to remove the prefix.
See network.
Use to cause BGP to select two best routes to every destination as follows:
For external peers, BGP selects the best route from the complete set of routes
known to BGP.
For internal peers, BGP selects the best route from the set of routes BGP has
received from external and confederation peers.
Changes apply automatically whenever BGP subsequently runs the best-path
decision process for a destination prefix; that is, whenever a best route is picked
for a given prefix.
The behavior enabled by this command is the default behavior for the E Series
router running software releases lower than 5.0.0.
The command is disabled by default.
Example
host2(config-router)#bgp advertise-best-external-to-internal
Use the no version to restore the default condition, wherein BGP selects one best
route for each destination from the complete set of routes; if the best route was