Dispatcher's mac forwarding requires extra steps when configuring the loopback on back-end AIX 5.x servers
 Technote (troubleshooting)
 
Problem(Abstract)
The mac forwarding method requires aliasing the loopback device on server machines that are being load-balanced. AIX 5.x servers require additional steps when configuring the loopback device.
 
Resolving the problem
When using the Dispatcher's mac forwarding method, the follow these steps to set up AIX 5.x server machines for load balancing:
Step 1. Alias the loopback device. Type:
ifconfig lo0 alias cluster_address netmask netmask_value

For example: ifconfig lo0 alias 9.27.176.131 netmask 255.255.255.0

Step 2. Check for an extra route. Type:
netstat -nr

Sample output:

Routing tables:

Route Tree for Protocol Family 2 (Internet):
Destination
Gateway
Flags
Refs
Use
If
PMTU
Exp
Groups
default
9.27.176.1
UGc
0
0
en0
-
-
9.27.23.42
9.27.176.1
UGHW
1
19
en0
-
-
9.27.176/24
9.27.176.58
U
4
11726
en0
-
-
=>
9.27.176/24
9.27.176.131
U
0
8
lo0
-
-
9.27.176.58
127.0.0.1
UGHS
23
157640
lo0
-
-
9.44.5.140
9.27.176.1
UGHW
0
84919
en0
-
1
10.0.7/24
10.0.7.4
U
0
3
en1
-
-
10.0.7.4
127.0.0.1
UGHS
0
0
lo0
-
-
10.5.32/24
10.5.32.4
U
0
2
tr0
-
-
10.5.32.4
127.0.0.1
UGHS
0
1
lo0
-
-
127/8
127.0.0.1
U
3
136835
lo0
-
-

Route Tree for Protocol Family 24 (Internet v6):
Destination
Gateway
Flags
Refs
Use
If
PMTU
Exp
Groups
::1
::1
UH
0
0
lo0
16896
-

If there is an extra route, you will see the network portion of the alias you just added with the an interface of lo0. Delete this route to prevent packets destined for the network from going through the loopback address.


Step 3. Delete any extra route
For example : route delete 9.27.176/24 9.27.176.131

Step 4. Verify server is properly configured.
1. Type: arp -d cluster (This removes the cluster address from the arp cache.)

2. From another machine, type: ping cluster (There should be no response. If there is a response, ensure that you did not ifconfig the cluster address to the interface and that no machine has a published arp entry to the cluster address.)

3. From another machine, ping the back-end server. Then, immediately type:
arp -s MEDIA cluster server_mac_address
where MEDIA is either 802.3, 802.5, or FDDI depending on the media type.

To unconfigure the loopback address, type:
ifconfig lo0 delete cluster_address netmask netmask_value
 
 
Cross Reference information
Segment Product Component Platform Version Edition
Application Servers WebSphere Edge Server Load Balancer AIX Edge Server 2.0 GA, Edge Server 2.0 NLV, Edge Server 2.0 PTF1, Edge Server 2.0 PTF2, Edge Server 2.0.x
Application Servers Runtimes for Java Technology Java SDK
 
Historical Number
85277
 
 


Document Information


Product categories: Software > Application Servers > Distributed Application & Web Servers > WebSphere Application Server > Edge Component
Operating system(s): AIX
Software version: 5.0
Software edition:
Reference #: 1116866
IBM Group: Software Group
Modified date: Aug 19, 2003