Bgp Permanent Network; Bgp-Rib Feedback Mechanism For Update Generation - Cisco ASR 9000 Series Configuration Manual

Implementing BGP

BGP Permanent Network

BGP permanent network feature supports static routing through BGP. BGP routes to IPv4 or IPv6 destinations
(identified by a route-policy) can be administratively created and selectively advertised to BGP peers. These
routes remain in the routing table until they are administratively removed.
A permanent network is used to define a set of prefixes as permanent, that is, there is only one BGP
advertisement or withdrawal in upstream for a set of prefixes. For each network in the prefix-set, a BGP
permanent path is created and treated as less preferred than the other BGP paths received from its peer. The
BGP permanent path is downloaded into RIB when it is the best-path.
The permanent-network command in global address family configuration mode uses a route-policy to identify
the set of prefixes (networks) for which permanent paths is to be configured. The advertise permanent-network
command in neighbor address-family configuration mode is used to identify the peers to whom the permanent
paths must be advertised. The permanent paths is always advertised to peers having the advertise
permanent-network configuration, even if a different best-path is available. The permanent path is not advertised
to peers that are not configured to receive permanent path.
The permanent network feature supports only prefixes in IPv4 unicast and IPv6 unicast address-families under
the default Virtual Routing and Forwarding (VRF).
Restrictions
These restrictions apply while configuring the permanent network:
• Permanent network prefixes must be specified by the route-policy on the global address family.
• You must configure the permanent network with route-policy in global address family configuration
• When removing the permanent network configuration, remove the configuration in the neighbor address

BGP-RIB Feedback Mechanism for Update Generation

The Border Gateway Protocol-Routing Information Base (BGP-RIB) feedback mechanism for update generation
feature avoids premature route advertisements and subsequent packet loss in a network. This mechanism
ensures that routes are installed locally, before they are advertised to a neighbor.
BGP waits for feedback from RIB indicating that the routes that BGP installed in RIB are installed in forwarding
information base (FIB) before BGP sends out updates to the neighbors. RIB uses the the BCDL feedback
mechanism to determine which version of the routes have been consumed by FIB, and updates the BGP with
that version. BGP will send out updates of only those routes that have versions up to the version that FIB has
installed. This selective update ensures that BGP does not send out premature updates resulting in attracting
traffic even before the data plane is programmed after router reload, LC OIR, or flap of a link where an
alternate path is made available.
To configure BGP to wait for feedback from RIB indicating that the routes that BGP installed in RIB are
installed in FIB, before BGP sends out updates to neighbors, use the update wait-install command in router
address-family IPv4 or router address-family VPNv4 configuration mode. The show bgp, show bgp neighbors,
and show bgp process performance-statistics commands display the information from update wait-install
configuration.
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mode and then configure it on the neighbor address family configuration mode.
family configuration mode and then remove it from the global address family configuration mode.
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.1.x
BGP Permanent Network
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