Cisco NCS 5500 Series Configuration Manual page 121

Implementing BGP
Command or Action
Step 4
bgp router-id ip-address
Example:
RP/0/RP0/CPU0:router(config-bgp-vrf)# bgp
router-id 172.16.9.9
Step 5
label-allocation-mode
Example:
RP/0/RP0/CPU0:router(config-bgp-vrf)#
label-allocation-mode per-ce
Step 6 address-family { ipv4 | ipv6 } unicast
Example:
RP/0/RP0/CPU0:router(config-vrf)#
address-family ipv4 unicast
Step 7 network { ip-address / prefix-length | ip-address
mask }
Example:
RP/0/RP0/CPU0:router(config-bgp-vrf-af)#
network 172.16.5.5
Step 8
aggregate-address address / mask-length
Example:
RP/0/RP0/CPU0:router(config-bgp-vrf-af)#
aggregate-address 10.0.0.0/24
Purpose
Configures a fixed router ID for a BGP-speaking router.
per-ce
Specifies either an IPv4 or IPv6 address family unicast and enters
address family configuration submode.
To see a list of all the possible keywords and arguments for this
command, use the CLI help (?).
Originates a network prefix in the address family table in the VRF
context.
Configures aggregation in the VRF address family context to
summarize routing information to reduce the state maintained in
the core. This summarization introduces some inefficiency in the
PE edge, because an additional lookup is required to determine
the ultimate next hop for a packet. When configured, a summary
prefix is advertised instead of a set of component prefixes, which
are more specifics of the aggregate. The PE advertises only one
label for the aggregate. Because component prefixes could have
different next hops to CEs, an additional lookup has to be
performed during data forwarding.
BGP Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
Configuring a VPN Routing and Forwarding Instance in BGP
• Configures The per-ce keyword configures the per-CE
label allocation mode to avoid an extra lookup on the PE
router and conserve label space (per-prefix is the default label
allocation mode). In this mode, the PE router allocates one
label for every immediate next-hop (in most cases, this would
be a CE router). This label is directly mapped to the next hop,
so there is no VRF route lookup performed during data
forwarding. However, the number of labels allocated would
be one for each CE rather than one for each VRF. Because
BGP knows all the next hops, it assigns a label for each next
hop (not for each PE-CE interface). When the outgoing
interface is a multiaccess interface and the media access
control (MAC) address of the neighbor is not known, Address
Resolution Protocol (ARP) is triggered during packet
forwarding.
• The per-vrf keyword configures the same label to be used
for all the routes advertised from a unique VRF.
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