Unanswered Question
Jun 19th, 2007


We have CLASS B IP address from RIPE ( Public IP address)

I need these addresses to be advertised to 2different ISP to whom I have internet connection.

Do I need to configure BGP at my internet router.

ISP 1 and ISP 2 both will be terminated on the same Router.

If someone has similar setup ; please advice.

I have this problem too.
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mohammedmahmoud Wed, 06/20/2007 - 00:41


The best practice answer is yes you need to run BGP, if you don't wish to run BGP, you can have those providers advertising them for you then use static routing between you and them, but they'll need to create route-objects on RIPE database attaching your IPs to their ASN.


Mohammed Mahmoud.

Amin Shaikh Wed, 06/20/2007 - 01:44

Thanks for your reply.

Can you ellaborate more what is the advantage or dis-advantage of BGP running at ISP or at my end.

Can I have a sample configuration.

The Idea is if one ISP goes down ; our services to users doesnt get disturb.

Automatic failover of services.

mohammedmahmoud Wed, 06/20/2007 - 03:56


The link provided by the other poster is very useful and have very nice examples and i would encourage you to review it, the main advantages in using BGP, would be that it gives you better control and flexibility, but if you don't want you can go for NATing and let the ISPs advertise your IPs (but as agreed they'll need route-objects are RIPE database).


Mohammed Mahmoud.

Amin Shaikh Wed, 06/20/2007 - 08:36


When u say advertise at ISP ; do u mean advertise the RIPE IP address one small block at ISP 1 and another Block at ISP 2

How does it work??

Please if you can explain....

mohammedmahmoud Wed, 06/20/2007 - 13:25


Yes you can have each ISP advertising part of your address space and thus you are able to control which traffic goes through which ISP, or you can advertise the whole address space from both ISP (asking one of the providers to do prepending in order to have a primary and backup scenario), but i'll strongly recommend that you run BGP to have full control over your network.


Mohammed Mahmoud.

Amin Shaikh Thu, 06/21/2007 - 00:05

Thanks Mohammed.

For my scenario If I run BGP at my end than what is required at ISP end.

I would be using One Router to terminate both ISP.

mohammedmahmoud Thu, 06/21/2007 - 00:33

Hi Amin,

If you run BGP from your side with both your providers on the same router, you'll just need to take care of filtration (in order not to act as a transit AS between the 2 ISPs, by making sure that you are not sending any routes received from one of the providers to the other), and then the other thing would be to decide whether you are going to advertise certain subnets to certain provider or just advertise your whole class to both providers but prepenging on one of them in order to have a primary and backup scenario.

At your provider end, you'll need your provider to relay your AS and IPs to the internet.

Please review this document as a sample configuration:

HTH, please do rate all helpful replies,

Mohammed Mahmoud


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