Cisco NCS 5500 Series

PurposeCommand or Action
Configures AS override on the PE router. This causes the PE router
to replace the CE’s ASN with its own (PE) ASN.
as-override
Example:
RP/0/RP0/CPU0:router(config-bgp-vrf-nbr-af)#
as-override
Step 16
This loss of information could lead to routing loops; to
avoid loops caused by as-override, use it in conjunction
with site-of-origin.
Note
Allows an AS path with the PE autonomous system number (ASN)
a specified number of times.
allowas-in [ as-occurrence-number ]
Example:
RP/0/RP0/CPU0:router(config-bgp-vrf-nbr-af)#
allowas-in 5
Step 17
Hub and spoke VPN networks need the looping back of routing
information to the HUB PE through the HUB CE. When this
happens, due to the presence of the PE ASN, the looped-back
information is dropped by the HUB PE. To avoid this, use the
allowas-in command to allow prefixes even if they have the PEs
ASN up to the specified number of times.
Specifies a routing policy for an inbound route. The policy can be
used to filter routes or modify route attributes.
route-policy route-policy-name in
Example:
RP/0/RP0/CPU0:router(config-bgp-vrf-nbr-af)#
route-policy pe_ce_in_policy in
Step 18
Specifies a routing policy for an outbound route. The policy can
be used to filter routes or modify route attributes.
route-policy route-policy-name out
Example:
RP/0/RP0/CPU0:router(config-bgp-vrf-nbr-af)#
route-policy pe_ce_out_policy out
Step 19
commit
Step 20
Resetting an eBGP Session Immediately Upon Link Failure
By default, if a link goes down, all BGP sessions of any directly adjacent external peers are immediately reset.
Use the bgp fast-external-fallover disable command to disable automatic resetting. Turn the automatic reset
back on using the no bgp fast-external-fallover disable command.
eBGP sessions flap when the node reaches 3500 eBGP sessions with BGP timer values set as 10 and 30. To
support more than 3500 eBGP sessions, increase the packet rate by using the lpts pifib hardware police
location location-id command. Following is a sample configuration to increase the eBGP sessions:
RP/0/RP0/CPU0:router#configure
RP/0/RP0/CPU0:router(config)#lpts pifib hardware police location 0/2/CPU0
RP/0/RP0/CPU0:router(config-pifib-policer-per-node)#flow bgp configured rate 4000
RP/0/RP0/CPU0:router(config-pifib-policer-per-node)#flow bgp known rate 4000
RP/0/RP0/CPU0:router(config-pifib-policer-per-node)#flow bgp default rate 4000
RP/0/RP0/CPU0:router(config-pifib-policer-per-node)#commit
BGP Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
113
Implementing BGP
Resetting an eBGP Session Immediately Upon Link Failure