Accumulated Interior Gateway Protocol Attribute - Cisco ASR 9000 Series Routing Configuration Manual

Accumulated Interior Gateway Protocol Attribute

Configuration
Configure your network topology with iBGP/eBGP running on your routers, before configuring this
Note
feature.
To configure BGP selective multipath on Router R4, use the following steps.
1 Configure Router R4 to accept selective multiple paths in your topology.
/* To configure selective multipath for iBGP/eBGP
RP/0/RSP0/CPU0:router(config)# router bgp 1
RP/0/RSP0/CPU0:router(config-bgp)# address-family ipv4 unicast
RP/0/RSP0/CPU0:router(config-bgp-af)# maximum-paths ibgp 4 selective
RP/0/RSP0/CPU0:router(config-bgp-af)# maximum-paths ebgp 5 selective
RP/0/RSP0/CPU0:router(config-bgp-af)# commit
/* To configure selective multipath for eiBGP
RP/0/RSP0/CPU0:router(config)# router bgp 1
RP/0/RSP0/CPU0:router(config-bgp)# address-family ipv4 unicast
RP/0/RSP0/CPU0:router(config-bgp-af)# maximum-paths eibgp 6 selective
RP/0/RSP0/CPU0:router(config-bgp-af)# commit
2 Configure neighbors for Router R4.
Routers R1 (1.1.1.1) and R2 (2.2.2.2) are configured as neighbors with the multipath option.
Router R3 (3.3.3.3) is configured as a neighbor without the multipath option, and hence the routes from
this router are not eligible to be chosen as multipaths.
RP/0/RSP0/CPU0:router(config-bgp)# neighbor 1.1.1.1
RP/0/RSP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast
RP/0/RSP0/CPU0:router(config-bgp-nbr-af)# multipath
RP/0/RSP0/CPU0:router(config-bgp-nbr-af)# commit
RP/0/RSP0/CPU0:router(config-bgp-nbr)# neighbor 2.2.2.2
RP/0/RSP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast
RP/0/RSP0/CPU0:router(config-bgp-nbr-af)# multipath
RP/0/RSP0/CPU0:router(config-bgp-nbr-af)# commit
RP/0/RSP0/CPU0:router(config-bgp-nbr)# neighbor 3.3.3.3
RP/0/RSP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast
RP/0/RSP0/CPU0:router(config-bgp-nbr-af)# commit
You have successfully configured the BGP selective multipath feature.
Accumulated Interior Gateway Protocol Attribute
The Accumulated Interior Gateway Protocol (AiGP)Attribute is an optional non-transitive BGP Path Attribute.
The attribute type code for the AiGP Attribute is to be assigned by IANA. The value field of the AiGP Attribute
is defined as a set of Type/Length/Value elements (TLVs). The AiGP TLV contains the Accumulated IGP
Metric.
The AiGP feature is required in the 3107 network to simulate the current OSPF behavior of computing the
distance associated with a path. OSPF/LDP carries the prefix/label information only in the local area. Then,
BGP carries the prefix/lable to all the remote areas by redistributing the routes into BGP at area boundaries.
The routes/labels are then advertised using LSPs. The next hop for the route is changed at each ABR to local
router which removes the need to leak OSPF routes across area boundaries. The bandwidth available on each
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
58
Implementing BGP