Adding Routes To The Routing Information Base; Bgp Dmz Aggregate Bandwidth - Cisco ASR 9000 Series Routing Configuration Manual

Implementing BGP
6 PE2 runs the enhanced BGP best-path calculation.
7 PE2 installs the best path in the RIB passing the appropriate cost community value.
8 PE2 RIB has two paths for 10.1.1.0/24: one with cost community cost2 added by EIGRP and another with
the cost community cost1 added by BGP. Because both the route paths have cost community, RIB compares
the costs first. The BGP path has the lower cost community, so it is selected and downloaded to the RIB.
9 PE2 RIB redistributes the BGP path into EIGRP with VRF. EIGRP runs a diffusing update algorithm
(DUAL) because there are two paths, and selects the BGP-redistributed path.
10 PE2 EIGRP advertises the path to CE2 making the path the next hop for the prefix to send the traffic over
the MPLS network.

Adding Routes to the Routing Information Base

If a nonsourced path becomes the best path after the best-path calculation, BGP adds the route to the Routing
Information Base (RIB) and passes the cost communities along with the other IGP extended communities.
When a route with paths is added to the RIB by a protocol, RIB checks the current best paths for the route
and the added paths for cost extended communities. If cost-extended communities are found, the RIB compares
the set of cost communities. If the comparison does not result in a tie, the appropriate best path is chosen. If
the comparison results in a tie, the RIB proceeds with the remaining steps of the best-path algorithm. If a cost
community is not present in either the current best paths or added paths, then the RIB continues with the
remaining steps of the best-path algorithm. See
the BGP best-path algorithm.

BGP DMZ Aggregate Bandwidth

BGP supports aggregating dmz-link bandwidth values of external BGP (eBGP) multipaths when advertising
the route to interior BGP (iBGP) peer.
There is no explicit command to aggregate bandwidth. The bandwidth is aggregated if following conditions
are met:
• The network has multipaths and all the multipaths have link-bandwidth values.
• The next-hop attribute set to next-hop-self. The next-hop attribute for all routes advertised to the specified
• There is no out-bound policy configured that might change the dmz-link bandwidth value.
neighbor to the address of the local router.
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
BGP DMZ Aggregate Bandwidth
BGP Best Path Algorithm, on page 39 for information on
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