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Same IP in DC and DR- What to do?

Dear Seniors,

I am new in this kinds of big deployment. OK, I have 2 Internet Service Provider (ISP), ISP-A and ISP-B and also have 2 DC sites and DR sites with same ISP's. I have also own register ASN with /23 block IP's. Following is my diagram.site_sample.jpg


I have a site in my web server what are sync with DR web server. So, I want my visitor can access my web site using one single ip resolution against the my FQDN. no required any dns refresh or any dns job. 

Need Help.







If you would like to direct the inbound traffic to the server via a single primary path? it would come down to what the ISP will let you advertise to it in terms of subnets.. I did something like it before because the ISP allowed me to advertise a smaller subnet like a /26 from one of the locations.. As well as the overall summary route.. In your case it is /23


So in that case the inbound traffic could come into the site B rather than site A where you may have an overlapped subnet ??

Dear Chrisgray1,

Thank you for your reply. In my case, i have /23 but there the problem is i am unable to route same network to my isp's two different network. I have share the following example.

I have and my isp have two different network for DC ( and DR( now my isp  cannot ebgp with my same network with their different network. So, i have break my network with 2 different /24 network. and then advertise with my DC ( site and with my DR ( So, in that case how i can unique my IP for my single site without help of dns failover?



There are 2 methods to solve this.

1) Use cisco anycast, below is a good introduction of the anycast topology.

2) Use load balancer in front of webserver.

You can prepend the as-path by 2-3 ASN additional for the prefix /24 on DR router for the 2 isp.
This will allow the incoming traffic to flow into the dc router without touching anything on main dc router.

For the webserver, you need to add load balancer and put your main and backup webserver on private ip and put the public webserver ip on the loadbalancer.

Once again, it depends on your company budget.

Hope it helps.

Dear Whitegrape,


Thank you very much for your solution. But i am really new in this job. Can you give me a better understanding to use my diagram. Because in your shared document they use only one router in the top of the diagram and also use same subnet for their second hop router. So, it is confusing for me.