2 ISP,s failover with BGP 1 customer router

[juancarlosmartinez]

Hi Guys,

I never did this implementation before, Currently the company  WAN is  connected to Cox thru BGP, but I want to fail over to ATT when Cox fails.

How can I do that.

Right now ATT just deliver the router for the fail over. It looks my router need to manage the fail-over system correct??? (multihoming)?

thanks for the help.....

[Mark Malone · Accepted solution]

Hey what you can do on one of your BGP neighbours under your process on your local router is at the end attach route-map and set the localpref to be more than 100 making it less preferred as the default will be a 100 from both ISPs

neighbor 1.1.1.1 route-map LOCALPREF in

route-map LOCALPREF permit 10
 set local-preference 200

[Erico Verissimo]

Mark,

It is so nice config. One session is always preferred and when it goes down the other one can route paths and prefixes. 

[Erico Verissimo]

Hi Juan,

I have this scenario here. By default the BGP doesn't do loadbalance between the links, instead that it will choose the best path to reach any network. So, you will have two BGP session established and receiving prefix from both. You have be sure these prefixes are on both BGP sessions, in this scenario when some link goes down the other one there are the BGP router table to route the paths. It is very important control the transit situation. Are your scenario MPLS or Internet?

Best regards.

Érico

[juancarlosmartinez]

Hi Erico,

Is internet......

[Erico Verissimo]

Hi Juan,

The config posted by Mark is more applicable for this scenario. In my case I use both links for data traffic and my net is MPLS.

[juancarlosmartinez]

Thanks Erico and Mark

[Masoud Pourshabanian]

Hello,

Just make sure your AS will not be a transit AS for two ISPs.

Configure these commands on both routers

I supposed you are getting only default route. Add more routes to the prefix-list if you are receiving more routes. Remove it if you are receiving full BGP routes.

on COX
ip prefix-list MY-Addresses permit 100.100.0.0/23 [ your IP addresses]
ip prefix-list default permit 0.0.0.0/0
neighbor 1.1.1.2 prefix-list default in   [You only receive default route ]
neighbor 1.1.1.2 prefix-list MY-Addresses out  [You only advertise your IP addresses]

on ATT
ip prefix-list MY-Addresses permit 100.100.0.0/23
ip prefix-list default permit 0.0.0.0/0
neighbor 2.2.2.2 prefix-list default in
neighbor 2.2.2.2 prefix-list MY-Addresses out

Hope it helps,

Masoud

[juancarlosmartinez]

Thanks SO much Masoud....I appreciated....

[juancarlosmartinez]

On question,Masoud

Because I do not have a access to the Cox and ATT routers the ISP guys will do that on their routers?

correct?

Thnanks

[Masoud Pourshabanian]

Hello,

By on ATT and on COX, I meant, on your routers connected to COX and ATT link. You need to set those commands on you router to advertise only your own IP addresses. If you do not do that, you may become a transit AS and advertise other AS IP addresses.

I suppose you have access to your own routers. Are they managed by COX and ATT?

Masoud

[juancarlosmartinez]

Ok, Thanks for explaining; Yes I have access to the company router;

[Sudeb Das]

On u r router u need to increase weight or local-pref as people are suggesting to u. 

Also u need to take care that u don't become a transit path once any ISP fails. For that u can configure - as-path access-list. 

Following example will block as 1234 to reach as 5678

ip as-path access-list 100 deny _1234_
ip as-path access-list 100 permit .*
ip as-path access-list 101 deny _5678_
ip as-path access-list 101 permit .*

neighbor 1.2.3.4 filter-list 101 out   (neighbor 1234 )

neighbor 5.6.7.8 filter-list 100 out    (neighbor 9829)

Happy Routing 

[juancarlosmartinez]

Thanks Sudeb for you help too. I appreciated