BGP multihoming...Dual edge routers connected with dual routers of 2 ISPs

[mohsin.khan]

Please find attached the topology...

Here are some requirements.

-          ISP-1 Primary and ISP-2 Secondary will be used for outgoing traffic of 10.10.15.0/24 and 10.10.8-14.0 respectively.

-          In case link to ISP-1 Primary goes down, 10.10.15.0/24 should be advertised to ISP-1 Secondary.

-          In case link to ISP-2 Primary goes down, 10.10.8-14.0 should be advertised to ISP-2 Secondary.

-          In case Edge-1 router goes down, 10.10.15.0/24 should be advertised from Edge-2 router to ISP-1 secondary, and 10.10.8-14.0 should be advertised from Edge-2 router to ISP-2 Primary.

-          In case Edge-2 router goes down, 10.10.15.0/24 should be advertised from Edge-1 router to ISP-1 Primary, and 10.10.8-14.0 should be advertised from Edge-1 router to ISP-2 Secondary.

I have defined some attributes, but i m very much shaky as they will not fulfil above requirements. Looking for some expert opinions.

regrards,

Mohsin

[Giuseppe Larosa]

Hello Mohsin,

you can use local preference to pick up the preferred received route

For the routes you are advertising to the upstream providers you need to use AS path prepending and BGP communites  to signal your preference in return path.

the logic is similar you need to change action "low local-preference" in set as-path prepend 33333 33333  (you can prepend only your own AS number or you will have issues)

to set a community you can use set community community-list-number additive

you need to agree with ISPs to what BGP communities to use they need to be meaningful for them

to advertise BGP communities you need neigh x.x.x.x send-community command for each peer

Hope to help

Giuseppe