BGP Load Sharing: Multihomed to Two ISPs Through Multiple Local Routers

BGP Load Sharing: Multihomed to Two ISPs Through Multiple Local Routers BGP selects only the single best path to a destination among the BGP paths that are learned from different ASs, which makes load balancing impossible. But, load sharing is possible in such multihomed BGP networks. On the basis of predetermined policies, traffic flow is controlled with different BGP attributes. This section discusses the multihoming configuration that has the most frequent use. The configuration shows how to achieve load sharing. See the Network Diagram, in which the multihome of AS 100 achieves reliability and load sharing. CONFIGURE: R1: conf t interface g0/0 ip address 192.168.31.1 255.255.255.0 ! interface g0/1 ip address 192.168.21.1 255.255.255.0 ! ip as-path access-list 1 permit ^300$ ! route-map AS-300-INCOMING permit 10 match as-path 1 set local-preference 200 ! ! access-list 10 permit 10.10.20.0 0.0.0.255 access-list 20 permit 10.10.10.0 0.0.0.255 ! route-map AS-300-OUTGOING permit 10 match ip address 10 set as-path prepend 100 100 100 ! route-map AS-300-OUTGOING permit 20 match ip address 20 ! router bgp 100 no synchronization bgp log-neighbor-changes network 10.10.10.0 mask 255.255.255.0 network 10.10.20.0 mask 255.255.255.0 neighbor 192.168.21.2 remote-as 100 neighbor 192.168.21.2 next-hop-self neighbor 192.168.31.3 remote-as 300 neighbor 192.168.31.3 route-map AS-300-INCOMING in neighbor 192.168.31.3 route-map AS-300-OUTGOING out no auto-summary end wr ! ! R2: interface g0/1 ip address 192.168.21.2 255.255.255.0 ! interface g0/0 ip address 192.168.42.2 255.255.255.0 ! ip as-path access-list 1 permit ^400$ ! route-map AS-400-INCOMING permit 10 match as-path 1 set local-preference 150 ! ! access-list 10 permit 10.10.10.0 0.0.0.255 access-list 20 permit 10.10.20.0 0.0.0.255 ! route-map AS-400-OUTGOING permit 10 match ip address 10 set as-path prepend 100 100 100 ! route-map AS-400-OUTGOING permit 20 match ip address 20 ! router bgp 100 no synchronization bgp log-neighbor-changes network 10.10.10.0 mask 255.255.255.0 network 10.10.20.0 mask 255.255.255.0 neighbor 192.168.21.1 remote-as 100 neighbor 192.168.21.1 next-hop-self neighbor 192.168.42.4 remote-as 400 neighbor 192.168.42.4 route-map AS-400-INCOMING in neighbor 192.168.42.4 route-map AS-400-OUTGOING out no auto-summary end wr VERIFY: show ip bgp show ip route 🔔 Subscribe to my YouTube channel: https://www.youtube.com/@FerdsTheNetworkGuy 📺 Playlist of all my videos on BGP: https://www.youtube.com/playlist?list=PLY9lFnUTS2PhDnChTQr2SASJ9kRnbK19T Facebook Page: https://www.facebook.com/Ferdsthenetworkguy References: Load Sharing When Dual-Homed to One Internet Service Provider (ISP) Through a Single Local Router: https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13762-40.html How Does Load Balancing Work?: https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/5212-46.html BGP Multipath: https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html#anc5 BGP Best Path Selection Algorithm: https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html #cisco #ccna #ccnp #ccie