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Load Balancing Issue on SMTP server as one of the server is getting over utilized and one is under utilized

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Hello Team ,


We have mail servers load balacing configured in our environment with persistency configured ( source ip with time out value 20 minutes). 

Load balancing method chosen is least connection.


One of the back end server is getting over utilized and one is under utilized .

Any body can advise if the persistency is required here or not (also what should be the time out value)

Also what should be the optimum load balancing method for this type of traffic to work optimally .

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Are you using a specific smtp server type? It might have more specific recommendations.

Also, since you are load balancing based on source ip, are the client ips visible to the adc or are they coming through an intermediate proxy so that all clients look like one ip address,  which could be imbalancing or skewing your results.



If you look at this 13.1 article for MS Exchange load balancing on the ADC and look at the pre Office 2016 section, you can see the basic smtp only load balancing.  Hard to say whether USIP mode is or isn't required in your scenario:  https://docs.citrix.com/en-us/citrix-adc/current-release/load-balancing/load-balancing-common-protocols/lb-microsoft-exchange-server.html


This reference specifically:

Support for SMTP:

For the following configuration, USIP must be enabled so that the CAS servers can see the sending SMTP server’s IP address for validation. This configuration also requires that the default gateway of the CAS server is configured to point at the ADC appliance’s SNIP address.


add lb vserver CAS_vserver_smtp TCP {HTTP Public IP} 25 -persistenceType SOURCEIP -timeout 60 -lbMethod LEASTCONNECTION -cltTimeout 30 add serviceGroup CAS_servicegroup_smtp TCP -maxClient 0 -maxReq 0 -cip DISABLED -usip YES -SP OFF -useproxyport YES -cltTimeout 30 -svrTimeout 30 -CKA NO -TCPB NO -CMP NO bind serviceGroup CAS_servicegroup_smtp {CAS-1 Server} 25 -CustomServerID "\"None\"" bind serviceGroup CAS_servicegroup_smtp {CAS-2 Server} 25 -CustomServerID "\"None\"" bind lb vserver CAS_vserver_smtp CAS_servicegroup_smtp



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