Advertised Network Ranges - BGP Question

[JohnTylerPearce]

Hey Guys,

Let's say I have three different datacenters, and I have a 1.0.0.0/22. My Network Range is 1.0.0.0,1.0.1.0,1.0.2.0,and 1.0.3.0.

So, let's say I have ISP1 and ISP2, can I advertise all network ranges out each ISP? Because, I thought, ISPs were allowd to advertise out

only a certain amount of IPs assigned by IANA. I wanted to do this, so If I have a server on 1.0.1.50, if ISP1 goes down, then a user can still get to the server at 1.0.1.50, through ISP2?

[Richard Burts]

John

I am not sure where you got the idea that an Internet Service Provider is limited in the number of registered prefixes that it can accept or that it can advertise. But I do not believe that this is the case - especially if we are talking about having registered provider independent address space. If you have 4 registered address ranges then your provider should accept your advertisement of them - or of 8 of them - or however many.

HTH

Rick

Sent from Cisco Technical Support iPhone App

[antonio.guirado]

Hello,

BGP let you do everything. You can think in the following routing policy:

- 1.0.0.0/23 and 1.0.0.0/22 for ISP A

- 1.0.0.2/23 and 1.0.0.0/22 for ISP B

This does that 1.0.0.0/23 is prefered by ISP A and 1.0.0.2/23 by ISP B. If there is a problem in

an ISP, then still have a backup through the other ISP (longer prefix). Now, you know the download

path.

Your policy can also be configured. In this case, path traffic will be based on AS number in the path. You can not

controll the traffic. Perhaps, it comes from ISP A or ISP B.

Notice that this is for download traffic. You should also think in upload traffic. The most simple is use

always an ISP (A or B). Balancing traffic in output is difficult.

Anyway when you decide your policy you should talk to your ISP because it must accept it. ISP can

configure filters to accept only the policy that you tell it. This point is very important. ISP must agree

your policy BGP routing.

Regards

[blau grana]

Hello John,

Is 1.0.0.0/22 range yours, or is it purchased from ISP? Do you have your own public AS number?

- both prefix and AS have to be yours (in your administration) to be able to advertise prefix via both ISPs.

Best Regards

Please rate all helpful posts and close solved questions

[paul driver]

Hello all,

I supose you can get around it by translation?

Two public ip ranges are advertised to their relative ISP's routers- However lets say ISP1 range is also used as Inside local addressing and natted on the router facing ISP2  with an ISP2 public address, This would solve advertising ISP1 to ISP2 and the other away around.

Make any sence, please share your thoughts?

res

Paul

Please don't forget to rate any posts that have been helpful.

Thanks.

[JohnTylerPearce]

Thanks for all the information guys. I was able to answer my own question lol. I should have wrote the question better.

Basically, one would need to talk to each ISP, and make sure that there ok with them putting a static route to the network advertised so that if traffic does come through that ISP, it will know that when it gets to that point to route traffic to the CE basically.