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Re: [Xen-users] Networking on Xen box

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Subject: Re: [Xen-users] Networking on Xen box
From: Simon Hobson <linux@xxxxxxxxxxxxxxxx>
Date: Fri, 28 Nov 2008 17:13:21 +0000
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Stephen Liu wrote:

Host - Debian Etch Workstation
Guest01 - mail server for routing
Guest02 - mail server, hostname01. localIP01, domain01
Guest03 - mail server, hostname02, localIP02, domain02
Guest04 - mail server, hostname03, localIP02, domain03

all mail servers running postfix as MTA on Debian Etch.

single (one) external IP with all ports forwarded to Guest01 except
port 53 which is forwarded to the DNS server, also running on a guest
of the Xen box.

Guest01 routes all incoming mails according to their domains to
respective mail servers.  All outgoing mails are sent via the routing
mail server, Guest01, to Internet.

The system is working nicely on Intranet.  Mail client, Evolution, on
workstations connected to local network, the Intranet, can send/receive
mails on the mail servers.  Server settings on mail client work on
either local IP or on hostname.

My question is if the workstation is on remote site, not on local
network.  What will be the server settings on the mail client.  If on
external IP how can the remote mail client find the mail server which
it needs to connect.  Please shed me some light.  TIA

This has nothing whatsoever to do with Xen - it is a standard networking problem in working around a broken network. <rant>NAT == Broken, no if's, but's or maybe's, it's BROKEN. The sooner people realise that NAT isn't an answer, it's part of the problem, and we move to IPv6 the better</rant>

Quite simply, you need to port forward whatever ports you use for client access to the appropriate server. BUT, you have 3 (or 4) servers the clients could need to access. Therefore you will need to use different ports to access different servers. Eg, if you use IMAP, then you would be able to use the standard port on one server, but would have to use different ports for the others.

Alternatively, get your clients to use a VPN to access the local network.

Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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