Cisco NCS 5500 Series

RP/0/RSP0/CPU0:router(config-bgp)# neighbor 10.0.0.1
RP/0/RSP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast
RP/0/RSP0/CPU0:router(config-bgp-nbr-af)# maximum-prefix 1000 discard-extra-paths
RP/0/RSP0/CPU0:router(config-bgp-vrf-af)# commit
The following screen output shows details about the discard extra paths option:
RP/0/0/CPU0:ios# show bgp neighbor 10.0.0.1
BGP neighbor is 10.0.0.1
Remote AS 10, local AS 10, internal link
Remote router ID 0.0.0.0
BGP state = Idle (No best local address found)
Last read 00:00:00, Last read before reset 00:00:00
Hold time is 180, keepalive interval is 60 seconds
Configured hold time: 180, keepalive: 60, min acceptable hold time: 3
Last write 00:00:00, attempted 0, written 0
Second last write 00:00:00, attempted 0, written 0
Last write before reset 00:00:00, attempted 0, written 0
Second last write before reset 00:00:00, attempted 0, written 0
Last write pulse rcvd not set last full not set pulse count 0
Last write pulse rcvd before reset 00:00:00
Socket not armed for io, not armed for read, not armed for write
Last write thread event before reset 00:00:00, second last 00:00:00
Last KA expiry before reset 00:00:00, second last 00:00:00
Last KA error before reset 00:00:00, KA not sent 00:00:00
Last KA start before reset 00:00:00, second last 00:00:00
Precedence: internet
Multi-protocol capability not received
Received 0 messages, 0 notifications, 0 in queue
Sent 0 messages, 0 notifications, 0 in queue
Minimum time between advertisement runs is 0 secs
For Address Family: IPv4 Unicast
BGP neighbor version 0
Update group: 0.1 Filter-group: 0.0 No Refresh request being processed
Route refresh request: received 0, sent 0
0 accepted prefixes, 0 are bestpaths
Cumulative no. of prefixes denied: 0.
Prefix advertised 0, suppressed 0, withdrawn 0
Maximum prefixes allowed 10 (discard-extra-paths) <<<<<<<<<<<<<<<<<<<<<
Threshold for warning message 75%, restart interval 0 min
AIGP is enabled
An EoR was not received during read-only mode
Last ack version 1, Last synced ack version 0
Outstanding version objects: current 0, max 0
Additional-paths operation: None
Send Multicast Attributes
Connections established 0; dropped 0
Local host: 0.0.0.0, Local port: 0, IF Handle: 0x00000000
Foreign host: 10.0.0.1, Foreign port: 0
Last reset 00:00:00
BGP Best-External Path
The best–external path functionality supports advertisement of the best–external path to the iBGP and Route
Reflector peers when a locally selected bestpath is from an internal peer. BGP selects one best path and one
backup path to every destination. By default, selects one best path . Additionally, BGP selects another bestpath
from among the remaining external paths for a prefix. Only a single path is chosen as the best–external path
and is sent to other PEs as the backup path. BGP calculates the best–external path only when the best path is
an iBGP path. If the best path is an eBGP path, then best–external path calculation is not required.
The procedure to determine the best–external path is as follows:
1
Determine the best path from the entire set of paths available for a prefix.
BGP Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
27
Implementing BGP
BGP Best-External Path