Configuring the server machines
About this task
Dispatcher will only load balance across servers that allow the loopback adapter to be configured with an additional IP address, for which the back-end server will never respond to ARP (address resolution protocol) requests.
Procedure
- Configure the loopback method.
Alias the network interface card or loopback device.
For most types of Linux, you can follow the instructions in the topic on aliasing the loopback device.
If you are using certain types of Linux operating systems, you may need to use an alternative method for aliasing the network card and loopback devices. Some versions of Linux systems issue ARP responses for any IP address configured on the machine on any interface present on the machine. If your system issues an ARP response, then follow the steps in the Configuring loopbacks with alternative methods topic.
- Check for an extra route. On some
operating systems, a default route may have been created and needs
to be removed. If problems are encountered with routing after aliasing,
remove the alias and add it back using a different netmask.Note: Any extra routes should be ignored on Windows 2003.
Check for an extra route on Windows operating systems with the following command:
route print
For example:- After route print is entered, a table similar to the following
example will be displayed. This example shows finding and removing
an extra route to cluster 9.67.133.158 with a default netmask of 255.0.0.0.
Active Routes: Network Address Netmask Gateway Address Interface Metric 0.0.0.0 0.0.0.0 9.67.128.1 9.67.133.67 1 9.0.0.0 255.0.0.0 9.67.133.158 9.67.133.158 1 9.67.128.0 255.255.248.0 9.67.133.67 9.67.133.67 1 9.67.133.67 255.255.255.255 127.0.0.1 127.0.0.1 1 9.67.133.158 255.255.255.255 127.0.0.1 127.0.0.1 1 9.255.255.255 255.255.255.255 9.67.133.67 9.67.133.67 1 127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1 224.0.0.0 224.0.0.0 9.67.133.158 9.67.133.158 1 224.0.0.0 224.0.0.0 9.67.133.67 9.67.133.67 1 255.255.255.255 255.255.255.255 9.67.133.67 9.67.133.67 1
- Find your cluster address under the “Gateway Address” column. If you have an extra route, the cluster address will appear twice. In the example given, the cluster address (9.67.133.158) appears in row 2 and row 8.
- Find the network address in each row in which the cluster address
appears. You need one of these routes and will need to delete the
other route, which is extraneous. The extra route to be deleted is
the one whose network address begins with the first digit of the cluster
address, followed by three zeroes. In the example shown, the extra
route is the one in row two, which has a network address of 9.0.0.0:
Network Address Netmask Gateway Address Interface Metric 9.0.0.0 255.0.0.0 9.67.133.158 9.67.133.158 1
- After route print is entered, a table similar to the following
example will be displayed. This example shows finding and removing
an extra route to cluster 9.67.133.158 with a default netmask of 255.0.0.0.
Check for an extra route on all Linux and UNIX systems with the following command:
netstat -nr
- Delete any extra route. You must delete the
extra route. Use the command for your operating system shown below:
route delete -net network_address cluster_address
route delete cluster_address cluster_address
route delete network_address cluster_address
Note: You must delete the extra route every time you reboot the server.To delete the extra route as shown in the ″Active Routes″ example above, enter:route delete 9.0.0.0 9.67.133.158
On Windows 2003, it is not possible to delete routes. Any extra routes should be ignored on Windows 2003. If problems are encountered with routing after aliasing, remove the alias and add it back using a different netmask.
Configure the workload partition (WPAR) as a backend server. Run all of the following commands on the machine that hosts the WPAR.
- Enable WPAR specific routing. Enter the
following command:
chwpar -i -I rtdest=default rtgateway=<Default_Gateway> <WPAR_name>
- Configure the IP address for the cluster on the loopback
interface of the WPAR.
chwpar -N interface=lo0 address=<cluster_IP_address> netmask=255.255.255.255 <WPAR_name>
Important: Only one WPAR per AIX operating system is supported. You can have an alias to the loopback in a WPAR, but it applies to the global partition and all WPARs defined in that partition. You can use one WPAR as a backend server in a partition but no more than one. WPARs are similar to Solaris Zones and the same restrictions apply there. You are creating a virtual operating system environment on a set of physical devices. The loopback is considered a physical device that is shared among the virtual images. One loopback exists. Any addresses that are an alias to the loopback are visible to all WPARs. As a result, you can create only one backend server instance that listens on the loopback across all WPARS in the partition.- Enable WPAR specific routing. Enter the
following command:
- Verify that the server is properly configured. To
verify if a backend server is properly configured, perform the following
steps from a different machine on the same subnet when the Load Balancer
is not running and cluster is unconfigured:
- Issue the c command. For example:
arp -d cluster
- Issue the ping command. For example:
ping cluster
There should be no response. If there is a response to the ping, ensure that you did not ifconfig the cluster address to the interface. Ensure that no machine has a published arp entry to the cluster address.
- Ping the back-end server, then immediately issue the
arp -a command For example:
arp -a
In the output from the command, you should see the MAC address of your server. Issue the command:arp -s cluster server_MAC_address
- Ping the cluster. You should get a response. Issue a http, telnet, or other request that is addressed to the cluster that you expect your back-end server to handle. Ensure that it works properly.
- Issue the arp -d command. For example:
arp -d cluster
- Ping the cluster. There should be no response. If there is a response, issue an arp cluster instruction to get the MAC address of the machine that is not configured correctly, and repeat steps 1 through 6.
- Issue the c command. For example:
Subtopics
Aliasing the network interface card or loopback device
Configuring loopbacks with alternative methods


File name: tcfg_configservers.html