In the following examples, the BGP Link Bandwidth feature is configured so BGP will distribute traffic proportionally to the bandwidth of each external link. The figure below shows two external autonomous systems connected by three links that each carry a different amount of bandwidth (unequal cost links). Multipath load balancing is enabled and traffic is balanced proportionally.

Note	The BGP Link Bandwidth feature functions for simple topologies that have a single path toward the exit points.

Caution

The BGP Link Bandwidth feature might not function properly if load balancing is required toward the exit points.

Figure 1. BGP Link Bandwidth Configuration

Router A Configuration

In the following example, Router A is configured to support iBGP multipath load balancing and to exchange the BGP extended community attribute with iBGP neighbors:

RouterA(config)# router bgp 100
 
RouterA(config-router)# neighbor 10.10.10.2 remote-as 100
 
RouterA(config-router)# neighbor 10.10.10.2 update-source Loopback 0
 
RouterA(config-router)# neighbor 10.10.10.3 remote-as 100
 
RouterA(config-router)# neighbor 10.10.10.3 update-source Loopback 0
 
RouterA(config-router)# address-family ipv4
 
RouterA(config-router-af)# bgp dmzlink-bw 
RouterA(config-router-af)# neighbor 10.10.10.2 activate
 
RouterA(config-router-af)# neighbor 10.10.10.2 send-community both
 
RouterA(config-router-af)# neighbor 10.10.10.3 activate
 
RouterA(config-router-af)# neighbor 10.10.10.3 send-community both
 
RouterA(config-router-af)# maximum-paths ibgp 6
 

Router B Configuration

In the following example Router B is configured to support multipath load balancing, to distribute Router D and Router E link traffic proportionally to the bandwidth of each link, and to advertise the bandwidth of these links to iBGP neighbors as an extended community:

RouterB(config)# router bgp 100
 
RouterB(config-router)# neighbor 10.10.10.1 remote-as 100
 
RouterB(config-router)# neighbor 10.10.10.1 update-source Loopback 0
 
RouterB(config-router)# neighbor 10.10.10.3 remote-as 100
 
RouterB(config-router)# neighbor 10.10.10.3 update-source Loopback 0 
RouterB(config-router)# neighbor 172.16.1.1 remote-as 200
 
RouterB(config-router)# neighbor 172.16.1.1 ebgp-multihop 1 
RouterB(config-router)# neighbor 172.16.2.2 remote-as 200
 
RouterB(config-router)# neighbor 172.16.2.2 ebgp-multihop 1 
RouterB(config-router)# address-family ipv4
 
RouterB(config-router-af)# bgp dmzlink-bw
 
RouterB(config-router-af)# neighbor 10.10.10.1 activate
 
RouterB(config-router-af)# neighbor 10.10.10.1 next-hop-self
 
RouterB(config-router-af)# neighbor 10.10.10.1 send-community both
 
RouterB(config-router-af)# neighbor 10.10.10.3 activate
 
RouterB(config-router-af)# neighbor 10.10.10.3 next-hop-self
 
RouterB(config-router-af)# neighbor 10.10.10.3 send-community both
 
RouterB(config-router-af)# neighbor 172.16.1.1
 activate 
RouterB(config-router-af)# neighbor 172.16.1.1 dmzlink-bw
 
RouterB(config-router-af)# neighbor 172.16.2.2 activate 
RouterB(config-router-af)# neighbor 172.16.2.2 dmzlink-bw
RouterB(config-router-af)# maximum-paths ibgp 6
RouterB(config-router-af)# maximum-paths 6
 

Router C Configuration

In the following example Router C is configured to support multipath load balancing and to advertise the bandwidth of the link with Router E to iBGP neighbors as an extended community:

RouterC(config)# router bgp 100
RouterC(config-router)# neighbor 10.10.10.1 remote-as 100
RouterC(config-router)# neighbor 10.10.10.1 update-source Loopback 0
RouterC(config-router)# neighbor 10.10.10.2 remote-as 100
RouterC(config-router)# neighbor 10.10.10.2 update-source Loopback 0
RouterC(config-router)# neighbor 172.16.3.30 remote-as 200
RouterC(config-router)# neighbor 172.16.3.30 ebgp-multihop 1
RouterC(config-router)# address-family ipv4 
RouterC(config-router-af)# bgp dmzlink-bw
 
RouterC(config-router-af)# neighbor 10.10.10.1 activate
RouterC(config-router-af)# neighbor 10.10.10.1 send-community both
RouterC(config-router-af)# neighbor 10.10.10.1 next-hop-self
RouterC(config-router-af)# neighbor 10.10.10.2 activate 
RouterC(config-router-af)# neighbor 10.10.10.2 send-community both
RouterC(config-router-af)# neighbor 10.10.10.2 next-hop-self 
RouterC(config-router-af)# neighbor 172.16.3.3 activate 
RouterC(config-router-af)# neighbor 172.16.3.3 dmzlink-bw
 
RouterC(config-router-af)# maximum-paths ibgp 6
RouterC(config-router-af)# maximum-paths 6
 

Router B

In the following example, the show ip bgp command is entered on Router B to verify that two unequal cost best paths have been installed into the BGP routing table. The bandwidth for each link is displayed with each route.

RouterB# show ip bgp 192.168.1.0

BGP routing table entry for 192.168.1.0/24, version 48
Paths: (2 available, best #2)
Multipath: eBGP
  Advertised to update-groups:
     1          2
  200
    172.16.1.1 from 172.16.1.2 (192.168.1.1)
      Origin incomplete, metric 0, localpref 100, valid, external, multipath, best
      Extended Community: 0x0:0:0
      DMZ-Link Bw 278 kbytes
  200
    172.16.2.2 from 172.16.2.2 (192.168.1.1)
      Origin incomplete, metric 0, localpref 100, valid, external, multipath, best
      Extended Community: 0x0:0:0
      DMZ-Link Bw 625 kbytes 

Router A

In the following example, the show ip bgp command is entered on Router A to verify that the link bandwidth extended community has been propagated through the iBGP network to Router A. Exit links are located on Router B and Router C. The output shows that a route for each exit link to autonomous system 200 has been installed as a best path in the BGP routing table.

RouterA# show ip bgp 192.168.1.0

BGP routing table entry for 192.168.1.0/24, version 48
Paths: (3 available, best #3)
Multipath: eBGP
  Advertised to update-groups:
     1          2
  200
    172.16.1.1 from 172.16.1.2 (192.168.1.1)
      Origin incomplete, metric 0, localpref 100, valid, external, multipath
      Extended Community: 0x0:0:0
      DMZ-Link Bw 278 kbytes
  200
    172.16.2.2 from 172.16.2.2 (192.168.1.1)
      Origin incomplete, metric 0, localpref 100, valid, external, multipath, best
      Extended Community: 0x0:0:0
      DMZ-Link Bw 625 kbytes
  200
    172.16.3.3 from 172.16.3.3 (192.168.1.1)
      Origin incomplete, metric 0, localpref 100, valid, external, multipath, best
      Extended Community: 0x0:0:0
      DMZ-Link Bw 2500 kbytes 

Router A

In the following example, the show ip route command is entered on Router A to verify the multipath routes that are advertised and the associated traffic share values:

RouterA# show ip route 192.168.1.0 

Routing entry for 192.168.1.0/24 
  Known via "bgp 100", distance 200, metric 0 
  Tag 200, type internal 
  Last update from 172.168.1.1 00:01:43 ago 
  Routing Descriptor Blocks: 
  * 172.168.1.1, from 172.168.1.1, 00:01:43 ago 
      Route metric is 0, traffic share count is 13 
      AS Hops 1, BGP network version 0 
      Route tag 200 
    172.168.2.2, from 172.168.2.2, 00:01:43 ago 
      Route metric is 0, traffic share count is 30 
      AS Hops 1, BGP network version 0 
      Route tag 200 
    172.168.3.3, from 172.168.3.3, 00:01:43 ago 
      Route metric is 0, traffic share count is 120 
      AS Hops 1, BGP network version 0 
      Route tag 200 

Related Documents

Standards

MIBs

RFCs

Technical Assistance

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.