path. Hence the previously allocated local label for the primary path must be retained on the primary PE for
some configurable time after the reconvergence. BGP Local Label Retention feature enables the retention of
the local label for a specified period. If no time is specified, the local lable is retained for a default value of
five minutes.
The retain local-label command enables the retention of the local label until the network is converged.
Command Line Interface (CLI) Consistency for BGP Commands
From Cisco IOS XR Release 3.9.0 onwards, the Border Gateway Protocol (BGP) commands use disable
keyword to disable a feature. The keyword inheritance-disable disables the inheritance of the feature
properties from the parent level.
BGP Additional Paths
The Border Gateway Protocol (BGP) Additional Paths feature modifies the BGP protocol machinery for a
BGP speaker to be able to send multiple paths for a prefix. This gives 'path diversity' in the network. The add
path enables BGP prefix independent convergence (PIC) at the edge routers.
BGP add path enables add path advertisement in an iBGP network and advertises the following types of paths
for a prefix:
• Backup paths—to enable fast convergence and connectivity restoration.
• Group-best paths—to resolve route oscillation.
• All paths—to emulate an iBGP full-mesh.
Add path is not be supported with MDT, tunnel, and L2VPN address families and eBGP
peerings.
Note
iBGP Multipath Load Sharing
When a Border Gateway Protocol (BGP) speaking router that has no local policy configured, receives multiple
network layer reachability information (NLRI) from the internal BGP (iBGP) for the same destination, the
router will choose one iBGP path as the best path. The best path is then installed in the IP routing table of the
router.
The iBGP Multipath Load Sharing feature enables the BGP speaking router to select multiple iBGP paths as
the best paths to a destination. The best paths or multipaths are then installed in the IP routing table of the
router.
When there are multiple border BGP routers having reachability information heard over eBGP, if no local
policy is applied, the border routers will choose their eBGP paths as best. They advertise that bestpath inside
the ISP network. For a core router, there can be multiple paths to the same destination, but it will select only
one path as best and use that path for forwarding. iBGP multipath load sharing adds the ability to enable load
sharing among multiple equi-distant paths.
Configuring multiple iBGP best paths enables a router to evenly share the traffic destined for a particular site.
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.1.x
OL-30423-03 53
Implementing BGP
Command Line Interface (CLI) Consistency for BGP Commands
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