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Application Delivery (ADX)

Occasional Contributor
Posts: 7
Registered: ‎01-11-2010

problem with Layer4 when load balancing mail server

I'm running a Virtual IP for my mail servers as given below . I'm using the command source-nat , since my server is not connected diarectly to serveriron . Emails are going out without any problem , but when receiving , the node2 is getting email source IP as layer4 IP . (For example , on node2 , if im receiving email from yahoo , the source IP is showing as layer4 , instead of showing yahoo IP . )and we are getting some problem due to this

server remote-name node2

weight 50 0
port smtp
port http
port http keepalive
port http url "HEAD /"
port imap4
port pop3

server virtual New_Hosting1

predictor least-conn
port http sticky concurrent
port imap4 sticky concurrent
port pop3 sticky concurrent
port smtp sticky concurrent
bind http node2 http
bind imap4 node2 imap4
bind pop3 node2 pop3
bind smtp node2 smtp

Occasional Contributor
Posts: 17
Registered: ‎08-19-2008

Re: problem with Layer4 when load balancing mail server


Can you share the network topology. If its just the http services on your server that needs to preserve client-ip , then check this thread for related conversation and the usage of client-ip insertion for HTTP to preserve client-ip.

But, If your topology is forcing you to use source-nat (i.e.  your remote real server (node2) has an alternate path/route back to clients which can't be changed) , then you have limited choices for most protocols (except http) as source-nat replaces the source-ip by definition to ensure traffic returns to the ServerIron.  Also, Maybe DSR is a possibility for your environment. Check here for some DSR info

Occasional Contributor
Posts: 7
Registered: ‎01-11-2010

Re: problem with Layer4 when load balancing mail server

Yes ..Our topology is forcing us to use source-nat and our server node2 is not diarectly conncted .It''s on a different segment and our server iron is on different segment .

basically i want to load balance the mail service (ie port 25) and is there is any way to do DSL ?



Super Contributor
Posts: 1,087
Registered: ‎12-13-2009

Re: problem with Layer4 when load balancing mail server


The SwitchBack feature applies to individual TCP/UDP ports. To configure the ServerIron for SwitchBack, you

enable the feature for individual TCP/UDP ports when configuring the virtual server. For example, when you

enable TCP port 25 (SMTP) on a virtual server, you can add the dsr parameter to enable SwitchBack for that port.

Traffic for other ports still returns through the ServerIron. The ServerIron does not translate the destination IP

address in client requests for the port with SwitchBack enabled. However, the ServerIron does still translate the

destination IP address in the client’s request to the real server’s IP address for other ports.

You also need to add a loopback on the real servers to answer on the VIP.

see page 3-146 of the Server Load Balancing Guide

I think this will do what you need.

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