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LB vServer with client-ip for smtp Exchange

Joachim Pfeiffer

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i need help for Loadbalancing smtp to Exchange.

We need to see the client ip at the Exchage System and not the LB vServer IP.

I test this with the command -usip=yes

Now, a new connection to the LB vServer hangs


Then i read about a SNIP for the Rote to the Exchange-Servers and set this SNIP

add ns ip -vServer DISABLED

After that, all Exchange Loadbalancers are down...

please help



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id you use the option -useip than the Netscaler will send all tha packets with the client ip and not the SNIP ip on the NEtscaler.

that means that the  Exchange serrver needs to have a route back to the client and this traffic will not pass through the NEtscaler.


Client ip can be inserted in http traffic as a header only. 

It can also be inserted in TCP traffic but than the application needs to be able to extract this client ip from an additiona tcp packet after the 3 way handshake.


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I need this Loadbalancer for smtp on Port 25, therefore i can not use client ip header.


with the option -usip yes e.g. "Use Client IP" in service,

a telnet on Loadbalancer Port 25 goes open, but does not provide any information of the smtp Server as when i connect directly ....


on different sources i read about a snip to the Network where the Exchange-Servers are .... but this does not working too


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  • 2 weeks later...

We get this request a lot, usually because clients want to manage SMTP allowed relaying per connector on exchange level. (e.g. allowed ip's internal relay, allowed ip's external relay, different types of authentication etc)

I believe there are 4 options:

- Use default subnet ip mode ( netscaler nats traffic from subnet ip) and do the source IP filtering on Netscaler instead of exchange 

- Use DSR mode as indicated above (return traffic completely bypass the netscaler, requires some config on exchange (loopback adapter,.. ))

- Use L3 Mode with USIP, and change default gateway on Exchange servers to Netscaler. I would try to avoid this as it can cause a lot of traffic routed through netscaler.

- Use GSLB where netscaler returns the IP for one of the SMTP servers based on a health check and from that moment the client connects directly to that SMTP server.  I personally prefer this option as it is generally easier to create a dns delegation to a NS HA pair  instead of doing fancy routing stuff.. 


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  • 2 weeks later...

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