Cisco ASR 9000 Series Routing Configuration Guide

Tuning the BGP Best-Path Calculation
Perform this task to change the default BGP best-path calculation behavior.
SUMMARY STEPS
1.
configure
2.
router bgp as-number
3.
bgp bestpath med missing-as-worst
4.
bgp bestpath med always
5.
bgp bestpath med confed
6.
bgp bestpath as-path ignore
7.
bgp bestpath compare-routerid
8.
commit
DETAILED STEPS
PurposeCommand or Action
configure
Step 1
Specifies the autonomous system number and enters the BGP
configuration mode, allowing you to configure the BGP
routing process.
router bgp as-number
Example:
RP/0/RSP0/CPU0:router(config)# router bgp 126
Step 2
Directs the BGP software to consider a missing MED attribute
in a path as having a value of infinity, making this path the
least desirable path.
bgp bestpath med missing-as-worst
Example:
RP/0/RSP0/CPU0:router(config-bgp)# bgp
bestpath med missing-as-worst
Step 3
Configures the BGP speaker in the specified autonomous
system to compare MEDs among all the paths for the prefix,
bgp bestpath med always
Example:
RP/0/RSP0/CPU0:router(config-bgp)# bgp
bestpath med always
Step 4
regardless of the autonomous system from which the paths
are received.
Enables BGP software to compare MED values for paths
learned from confederation peers.
bgp bestpath med confed
Example:
RP/0/RSP0/CPU0:router(config-bgp)# bgp
bestpath med confed
Step 5
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
88
Implementing BGP
Tuning the BGP Best-Path Calculation

Cisco ASR 9000 Series Specifications

General

Series	ASR 9000
Category	Network Router
Modular Design	Yes
Redundancy	Yes (Hardware and Software)
Operating System	Cisco IOS XR
Interfaces/Ports	10G, 40G, 100G, 400G Ethernet
Expansion Slots	Varies by model
Routing Protocol	BGP, OSPF, IS-IS, EIGRP
Management	CLI, SNMP, NETCONF
Power Supply	Redundant
Port Density	Varies by model
Power Supply Options	AC, DC
Memory	Varies by model
Storage	Varies by model
Dimensions	Varies by model
Weight	Varies by model