Juniper JUNOSE 11.2.X BGP AND MPLS, Configuration Manual

Page: 88 / 742

command, then BGP is notified as soon as the route becomes available in the IP routing
table or IP tunnel routing table.
•
For IPv4 addressing, specify a network-number and an optional network-mask . For IPv6
addressing, specify the IPv6 prefix.
•
You can specify a route map to filter network routes or modify their path attributes.
•
The default weight for network routes is 32768; use the weight keyword to modify the
weight in the range 0–65535.
•
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 137 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.
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 104 for information about the process BGP uses to determine best routes.
bgp advertise-best-external-to-internal
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.
Copyright © 2010, Juniper Networks, Inc. 52
JunosE 11.2.x BGP and MPLS Configuration Guide