BGP Link Bandwidth Unequal-Cost IBGP Load Balancing (Load Sharing)

The BGP Link Bandwidth feature can be implemented for unequal-cost IBGP load balancing. It utilizes the Link Bandwidth Extended Community to advertise a received EBGP route along with the bandwidth of the link that connects to the EBGP neighbor to IBGP neighbors. The bandwidth is encoded as 4 octets in IEEE floating point format, in the unit of bytes per second. The Link Bandwidth Extended Community should not be propagated outside of an AS, similar to the Local Preference attribute.
Note: The draft-ramachandra-bgp-ext-communities-08 defines the Link Bandwidth Extended Community but never made it to the final RFC 4360 – BGP Extended Communities Attribute.

Below shows that RT1 is able to achieve unequal-bandwidth load balancing with traffic sharing ratio proportional to the bandwidth of the inter-AS links.

RT1#sh ip bgp 192.168.2.0
BGP routing table entry for 192.168.2.0/24, version 5
Paths: (2 available, best #2, table Default-IP-Routing-Table)
Multipath: iBGP
Flag: 0x820
  Not advertised to any peer
  200
    35.35.35.5 from 13.13.13.3 (35.35.35.3)
      Origin IGP, metric 0, localpref 100, valid, internal, multipath
      DMZ-Link Bw 250 kbytes
  200
    24.24.24.4 from 12.12.12.2 (24.24.24.2)
      Origin IGP, metric 0, localpref 100, valid, internal, multipath, best
      DMZ-Link Bw 750 kbytes
RT1#
RT1#sh ip route 192.168.2.0
Routing entry for 192.168.2.0/24
  Known via "bgp 100", distance 200, metric 0
  Tag 200, type internal
  Last update from 24.24.24.4 00:00:13 ago
  Routing Descriptor Blocks:
  * 35.35.35.5, from 13.13.13.3, 00:00:13 ago
      Route metric is 0, traffic share count is 1
      AS Hops 1
      Route tag 200
    24.24.24.4, from 12.12.12.2, 00:00:13 ago
      Route metric is 0, traffic share count is 3
      AS Hops 1
      Route tag 200

RT1#