by Dan Schlimme

I recently had to load balance our Exchange SMTP Relay and IIS SMTP Relay.  Both of these require the use of DSR which I was unfamiliar with and wanted to share my experience.

Important Pieces of Information

• Netscaler Firmware
  • NS 10.5 61.11.nc
• Exchange Environment
  • Exchange 2010
• Server OS
  • Server 2012 R2
• Your vip needs to be on the same VLAN as your load balanced servers
• You will need a SNIP for the VLAN of your load balanced servers
• You will need to add the VLAN of your load balanced servers to your network port
• MAC based forwarding needs to be enabled

Netscaler and Server Networking configuration are the same for Exchange SMTP Relay and IIS SMTP Relay

Netscaler Configuration

• Add the VLAN you will be working with to your Netscaler
  • Navigate to System\Network\VLANs
    • Select Add
      • Enter the VLAN ID
      • Bind to the Interface you need
        • I tagged the traffic, but this may not be needed in your environment

• Add SNIP to the Netscaler on the VLAN you just added
  • Navigate to System\Network\IPs
    • Select Add
      • Enter the IP
      • Enter the Netmask
      • Select IP Type as Subnet IP
      • OPTIONAL STEP – Uncheck “Enable Management Access control to support the below listed applications”

• Add the servers you want to load balance
• Create the SMTP Monitor
  • Standard Parameters
    • Give it a name
    • Set the port number to 25

• Special Parameters
  • Select Script of nssmtp.pl
  • Set Dispatcher IP to 127.0.0.1
  • Set Dispatcher port to 3013

• Create the Service Group
  • Basic Settings Configuration
    • Give it a name
    • Set Protocol to ANY

• Settings Configuration
  • Select Use Proxy Port
  • Select Down State Flush
  • Select Use Client IP

• Monitor Configuration
  • Add the SMTP Monitor you created earlier
  • You also need to add a second monitor of TCP/Ping/ARP
    • I used ARP
      • This has something to do with learning the MAC address. I am not entirely certain.
• Service Group Members Configuration
  • Add the Servers you added earlier

• Create the Virtual Server
  • Basic Settings Configuration
    • Give it a name
    • Set Protocol to ANY
    • Assign IP
    • Set Redirection Mode to MAC Based

• Service and Service Groups Configuration
  • Bind the Service Group you created earlier
• Method Configuration
  • Set Load Balancing Method to Round Robin

• Persistence Configuration
  • Set Persistence to SourceIP

• Traffic Settings Configuration
  • Select Sessionless Load Balancing

• Your Virtual Server is now configured

Server Configuration

• Add a loopback network adapter
• Rename Ethernet adapter to Ethernet
• Rename the Loopback adapter to Loopback
• Open properties of the Loopback adapter
  • Uncheck everything except Internet Protocol Version 4 (TCP/IPv4)

• Select Internet Protocol Version 4 (TCP/IPv4) and select Properties
  • General Settings Configuration
    • Add the IP you used for your SMTP Virtual Server
    • Set the Subnet Mask to 255.255.255.255
    • Do not set DNS

• Advanced Configuration Settings
  • IP Settings
    • Uncheck Automatic metric
    • Set Interface Metric to 254
      • This prevents the ip from arping

• DNS
  • Uncheck Register this connection’s address in DNS

• WINS
  • Select Disable NetBIOS over TCP/IP

• From command line run the following commands with elevated privileges
  • netsh int ipv4 set int “Loopback” weakhostreceive=enabled weakhostsend=enabled
  • netsh int ipv4 set int “Ethernet” weakhostreceive=enabled
  • arp -d *
• Your Server is now configured for DSR

IIS SMTP Relay Configuration

• Open IIS on your Relay server
• Go to properties of your SMTP Virtual server in IIS
  • General Settings
    • You will see an IP in the middle, this is the IP of the Relay server itself.
    • Select Advanced next to the Relay Server IP

• Select Add
  • Choose the IP of the VIP created earlier
  • Set the port to 25

• Access Settings
  • Select Relay

Select Add

Add the VIP you created earlier

• IIS SMTP Relay is now configured

Exchange SMTP Relay Configuration

• Open Exchange Management Console
• Expand Server Configuration
  • Select Hub Transport
    • Select a Hub Transport

• Right Click on your SMTP Relay Receive Connector and Select Properties
  • If you do not already have an SMTP Relay Receive Connector, this link will help you create one
    • How to Configure a Relay Connector for Exchange Server 2010
  • Select the Network Tab

• In the “Use these local IP addresses to receive mail” section, select Add
  • Select “Specify an IP address”
  • Enter the VIP you created earlier
  • Set the Port to 25

• You now need to do the same step to all of your Hub Transport Servers
• Your Exchange SMTP Relay is now Configured

Read this if DSR and Netscaler isn’t working for you

https://discussions.citrix.com/topic/361612-exchange-and-source-ip/

As per the comment from rbarrick on the above article, I also found the same problem. I had more than one VIP with the same IP and even though they were disabled it would not connect until I deleted the disabled Virtual Servers with the same IP. I had them setup after following this article on Exchange Load balancing so when it came to configuring DSR I had multiple VIP’s with the same IP. Deleting them or changing the IP they use is the only solution. Hope this saves someone some head scratching.