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Re: LVS-NAT + SNAT is it impossible?

To: "LinuxVirtualServer.org users mailing list." <lvs-users@xxxxxxxxxxxxxxxxxxxxxx>
Subject: Re: LVS-NAT + SNAT is it impossible?
From: Josh Marshall <josh@xxxxxxxxxxxxxxxx>
Date: Fri, 14 Jul 2006 16:25:24 +1000
Hi,

Along similar lines to this I would like to know if it's possible to allow realservers behind a LVS-NAT to access virtual servers.

e.g. I have a pair of webservers and a pair of mailservers behind a single LVS-NAT machine. When a webserver emails the mailserver (hundreds of virtual domains so faking the dns would be a pain) it is not able to connect via the external IP address.

When I do a tcpdump I see that the request is going from the webserver to the firewall then to the mailserver, but the path back to the webserver is direct, and since it's the internal ip address of the mailserver rather than the ip address of the VIP the webserver doesn't recognise the reply.

Is there some way I can get the firewall to SNAT so that connections will go via the firewall correctly? I read somewhere that I could use mark tables but couldn't quite piece it all together.

Thanks,
Josh

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