Advanced routing question

[brea]

I have a problem that I need some help with.

I have two sites A-B. At both sites I need to advertise the same address space with an equal value, for bandwidth management and regional reasons.

Site A has a 50Mb link to site B and all routing is done through BGP.

Recently we had an outage where the 50Mblink was cutoff. It did not go down fully, just within the carrier network so the actual state on router A-B did not change but the traffic could not pass, which caused an outage.

Is there a way to ensure that BGP advertises only external in the event that this link goes down? I'm thinking that OSPF or something similar would need to be involved but am not sure how to implment it.

It would look like this.

1.1.1.0/24---RouterA----50MbFiberlink----RouterB---1.1.1.0/24
| |
| |
ISPA ISPB

Again wanting traffic to come through either RouterA or B in optimal situations but if the Fiber link goes down then traffic would go to whichever link your AS points to.

Thanks.

 

[lambent]

Questions:

1) Do you have a backup WAN connection between Router A and Router B other than the 50Mb Fiber link?
2) I don't quite understand why you can have the same subnet in Router A and Router B while you're running BGP between them? Or is it a typo?

 

[jneiberger]

I think brea is just advertising the same internal network to his ISPs from two border routers. However, I don't understand the question. Can you re-state it a different way? I'm not sure exactly what you want to accomplish.

John

 

[brea]

It's not a typo. The current environment needs to advertise the same IP address or subnet from both locations.

There is no backup WAN Connection between router A and router B.

And yes we are advertising the same network to seperate ISP's from the border routers.

TO be honest I am not exactly sure why we want to accomplish it either. I just know they want to do it. I am trying to do two things.

1. Identify the best way to do this, assuming there is no other way and I think there is.

2. Identify that other way. I have a pretty good idea in this area but I want to cover all bases.

To restate the question.

I have an application, let's say OWA to make it simple and I provide access to it for multiple companies so that they can access their mail.

I want to point them to one IP address and have the Servers in two disparate locations with the same IP address. Using BGP I should be able to advertise an active-active type of configuration where both locations advertise the same number of hops and then the remote end chooses it's location based on their relation to it.

Or in an Active-passive state where if one site goes down then traffic will route to the other location without problem.

I hope that clears it up some.

 

[jneiberger]

I think if you want multiple servers to exist in different locations with the same IP address then you should look at front-ending them with some sort of load balancer that can manage remote devices. Another thought would be to look into using anycast but that might be a bit too much to chew on for this application.

 

[brea]

The application is much more advanced than OWA. I was just using it as an example if people needed to apply something to the idea.

Loadbalancers are an option.

I'm not sure what anycast is. WIll have to look into it more, unless someone has a quick link or explanation.

 

[jneiberger]

http://www.domainsarefree.com/glossary/Anycast.html

It's really probably not a great idea for this application, it was just me thinking out loud.

 

[brea]

I realized that after looking at it.

 

[lambent]

Just want to confirm something...

In Router A, there are 3 interfaces:

Interface A = 1.1.1.0/24 (some kinds of LAN or server segment)
Interface B = Connection to ISP A
Interface C = Connection to Router B via fiber

In Router B, there are also 3 interfaces:

Interface D = 1.1.1.0/24 (Same purpose as Router A)
Interface E = Connection to ISP B
Interface F = Connection to Router A via fiber

Please correct me if I'm wrong, cos the text-based diagram appeared a little bit distorted to me.