BGP - Multihomed and Load Sharing

[kdagostino]

We would like to be able to "load share" between my 2 ISP connections - currently we receive only default routes from our ISPs:

router bgp 171

network 1.0.0.0

network 2.0.0.0

neighbor 10.10.10.10 remote-as 111

neighbor 10.10.10.10 route-map local out

neighbor 10.10.10.10 prefix-list ABC in

neighbor 20.20.20.20 remote-as 222

neighbor 20.20.20.20 route-map local out

neighbor 20.20.20.20 prefix-list ABC in

ip prefix-list ABC seq 5 permit 0.0.0.0/0

ip as-path access-list 10 permit ^$

route-map local permit 10

match as-path 10

** According to some docs I found on the website I can just create additonal route-maps with access-lists to segregate traffic accordingly. Has anyone tried this and if so, any suggestions? If not, any alternatives would be appreciated.

[thisisshanky]

I see, that you are trying to filter all routes from your 2 ISPs except for the default route. In this case, both default routes are announced by your ISPs via BGP. To loadbalance between the two, you need to give the command, "maximum-paths 2" under router BGP mode.

[kdagostino]

Can you elaborate? I cannot find anything on the maximum-paths command. Thanks again for any help.

[thisisshanky]

Since you want to load balance between both the ISPs using both the default routes, you need to install both the routes in the routing table. Since the default routes are advertised by neighboring ISPs, mostly all attributes of BGP will be same or similar, so that your router will be forced to select only one default route as the best route and install it on the routing table. ( the selection criteria used will be lowest router-id of the EBGP neighbor). So which ever ISP has the lowest router-id , his default route will be used.

To use both the routes, you need to give, the maximum-paths "N" command. N is a number from 2-6. Upto six parallel paths are supported. Syntax can be found in the following links.

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122sup/122csum/csum1/122csip2/1sfbgp1.htm#1183975

Hope that helps!