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New Member

Load Sharing with BGP


I have Cisco 3640 router with two t1 lines connected to two isp in the same router. I wanted to do a load sharing and i configured the BGP as following

router bgp abc

bgp log-neighbor-changes

network x.x.x.0 mask

network y.y.y.0 mask

neighbor x.x.x.x1 remote-as efg

neighbor x.x.x.x1 route-map isp1 in

neighbor y.y.y.y1 remote-as hij

neighbor y.y.y.y1 route-map isp2 in


ip classless

ip route x.x.x.x1

ip route y.y.y.y1

access-list 1 permit

access-list 2 deny

access-list 2 permit any

route-map isp1 permit 10

match ip address 1

set weight 100


route-map isap1 permit 20

match ip address 2


route-map isp2 permit 10

match ip address 1


route-map isp2 permit 20

match ip address 2

set weight 100

But when i tested i found out that all the connections are going through isp2 and none was going via isp1. My aim was to make all the connections till 127.x.x.x network to go via isp1 and from 128.x.x.x to go via isp2

Can some one adivce me what is the mistake i have made in the configuration.

Thanks in Advance


Re: Load Sharing with BGP

Route maps are usually used with AS-PATH list, not ip addresses or subnets.

Also, some ISPs influence traffic by implementing communities, you can check with your ISP and see what your options are.




Re: Load Sharing with BGP

I would just enable CEF and let it do per-destination load balancing. Get rid of all the route-map stuff but leave the default routes there. CEF will see the two equal-cost default routes and load-balance outbound traffic appropriately over the two links. Leave it at the default of per-destination rather than using per-packet since the links go to separate ISPs.

Another option if you want to ensure somewhat more optimal routing is to do the above but also accept customer routes only (*not* the full routing table) from each ISP. This will force all traffic to ISP-A's customers (i.e., networks directly connected to ISP-A) to go out the ISP-A link, and likewise for ISP-B. Any traffic destined to non-customers will be load balanced by CEF per above.

New Member

Re: Load Sharing with BGP

Thanks a lot. I will do as per user suggestion and get back if have any issues

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