Resilient Per-Ce Label Allocation Mode; How To Implement Bgp; Enabling Bgp Routing - Cisco ASR 9000 Series Configuration Manual

Implementing BGP

Resilient Per-CE Label Allocation Mode

The Resilient Per-CE Label Allocation is an extension of the Per-CE label allocation mode to support Prefix
Independent Convergence (PIC) and load balancing.
At present, the three label allocation modes, Per-Prefix, Per-CE, and Per-VRF have these restrictions:
• No support for ASR 9000 Ethernet Line Card and A9K-SIP-700
• No support for PIC
• No support for load balancing across CEs
• Temporary forwarding loop during local traffic diversion to support PIC
• No support for EIBGP multipath load balancing
• Forwarding performance impact
• Per-prefix label allocation mode causes scale issues on another vendor router in a network
In the Resilient Per-CE label allocation scheme, BGP installs a unique rewrite label in LSD for every unique
set of CE paths or next hops. There may be one or more prefixes in BGP table that points to this label. BGP
also installs the CE paths (primary) and optionally a backup PE path into RIB. FIB learns about the label
rewrite information from LSD and the IP paths from RIB.
In steady state, labeled traffic destined to the resilient per-CE label is load balanced across all the CE next
hops. When all the CE paths fail, any traffic destined to that label will result in an IP lookup and will be
forwarded towards the backup PE path, if available. This action is performed on the label independently of
the number of prefixes that may point to the label, resulting in the PIC behavior during primary paths failure.

How to Implement BGP

Enabling BGP Routing

Perform this task to enable BGP routing and establish a BGP routing process. Configuring BGP neighbors is
included as part of enabling BGP routing.
At least one neighbor and at least one address family must be configured to enable BGP routing. At least
Note
one neighbor with both a remote AS and an address family must be configured globally using the address
family and remote as commands.
Before You Begin
BGP must be able to obtain a router identifier (for example, a configured loopback address). At least, one
address family must be configured in the BGP router configuration and the same address family must also be
configured under the neighbor.
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Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.1.x
Resilient Per-CE Label Allocation Mode
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