Methods for having same IP address or segment in two location.

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Feb 11th, 2008
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We're designing a remote site disaster recovery center and are at the stage of developing a series of tests. An IBM mainframe is at both the main data center and at the remote one. Our mainframe folks want/need to be able to test the same applications on both mainframes and they don't want to change the IP address of the interface that supports those application.


For instance say all the TN3270 clients resolve the hostname IBMA to 192.168.100.12. Well the IBM test folks want 192.168.100.12 to not only be at the main data center, but also at the remote data center - so the clients don't have to change how they point to the applications.


What do other people do who have this requirement?


1. Do they have load balancers that redirect traffic to different backends depending on certain criteria?

2. Is the remote data center isolated from the main production network and accessed remotely by the testers - thereby insuring total separation from the same subnets and IP addresses?


I'm sure this problem has been addressed before and a rock-solid solution is available.

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Gilles Dufour Tue, 02/12/2008 - 00:02
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What I have seen is people using a loadbalancer with the RHI (Route Health Injection) feature.

Basically, the loadbalancer monitor the status of the mainframe, and if it is alive, it advertises a host route in the network.


Now, you can have the same host route advertised by 2 different sites.

Each router in the network should receive those 2 routes and based on your routing protocol, the closest one (the one w/ the best metric) should be selected.

So client from site-A will go to loadbalancer-A and client from side-B, will go to loadbalancer-B.


Now, if one mainframe goes down, the loadbalancer will stop advertising the associated route, and all the traffic will go to the remaining site.


You can also configure on the loadbalancer one site as backup to the other site.

So even if traffic comes to the loadbalancer with the down mainframe, it can forward the traffic to the other site.


All this is possible with the ACE or CSM.


Another solution is to use a GSS (Global Site Selector).

It's a device that acts as a dns server.

It can monitor the status of the mainframe and also provide a different dns response depending on the client.

Like this, you don't have to change the name of the mainframe, but you still need different ip.



Gilles.

stevek1 Wed, 04/16/2008 - 20:20
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Hi Gilles,

Is there any basic example ACE configs out there which provide the necessary commands just to get this feature working. I have the same requirement as detailed in this thread, but this is the first function of my ACE and have no need for the other features as yet.

The manuals have hundreds of pages of features, initially I just need the RHI setup for advertising a route to the same network at 2 Data Centres.

Cheers, SteveK

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