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IPsec VPN and loopback interface etc....

Hi all,

We are trying to setup a bulk SMS system to transmit SMSs.

I have to setup a connection with the service provider.

We have been told we need to use VPN over our link. We are connecting our sites through ATM since we both have ATM.

Here it the confusing part of the whole thing.

I have never setup VPNs but from other examples i have seen its quite straight forward. was until i had talk with the service provider engineer.

First of all, i was given a private IP of subnetted class A to use on my subinterface.

When i talked to the engineer he said i need to have 2 public IPs set up.

I have discussed with him and the outcome is this (even though he could not give me technical reasons for doing so ) :

I am going to use a subnetted class A IP on my ATM Subinterface.

Then he mentioned something about using one of the Public IPs on my loopback interface. And then he said i will use NAT with the second Public IP.

I have tried to get some sense for all these, but he could not help me. Maybe he was giving me general instructions of how they set this up. I require more technical reasons to back up the loopback with Public IP and the use of another NATed public IP.

Can some one give me example of what teh loopback interface is and what exactly is it used for in a VPN. Does his setup make sense ????

Please help me....if you need more claryfying for my situation please let me know.

Hope you can help ,



Re: IPsec VPN and loopback interface etc....


Loopback interface plays a noted role in keeping the VPN connectivity intact if the tunnel is being built with source as the loopback interface.

If in case you have 2 links and want to have vpn over both of them as a part of load balancing stuff or you want to have redundancy to be taken care without affecting the VPN connectivity though the physical links which gets you connected to the remote peer mite go down.

i agree that to reach the VPN peers to have the VPN connectivity you need to have the reachability to the peers which can be achieved by using a public ip in the form of loopback.

Also i doubt that your SP is running their Customer infrastructure with the private blocks and that may be the reason for giving the private ip to be configured under your sub interface.

The real puzzle here is using one more public ip which you say for NAT..may be the CAM or SM from the SP side can help u out..