Troubleshooting
Problem
The Load Balancer cluster address must be aliased to the server loopback adapter if:
- The server is load balanced by the IBM® WebSphere® Application Server Load Balancer.
- The Load Balancer is configured for MAC forwarding to this server.
Instructions for aliasing addresses to the loopback interface of Microsoft® Windows® are provided.
Resolving The Problem
The loopback adapter is not installed by default with Microsoft® Windows®.
Determine whether the loopback adapter is installed.
Issue the command: ipconfig /all
The loopback adapter is installed if output shows:
ipconfig /all
. . .
Ethernet adapter Ethernet <#>:
. . .
Ethernet adapter Ethernet <#>:
Connection-specific DNS Suffix . :
Description. . . . . . . . . . . . . . : Microsoft KM-TEST Loopback Adapter
Physical Address. . . . . . . . . : 02-00-4C-4F-4F-50
Description. . . . . . . . . . . . . . : Microsoft KM-TEST Loopback Adapter
Physical Address. . . . . . . . . : 02-00-4C-4F-4F-50
Or
Ethernet adapter Local Area Connection <#>:
Connection-specific DNS Suffix . :
Description. . . . . . . . . . . . . . : Microsoft Loopback Adapter
Connection-specific DNS Suffix . :
Description. . . . . . . . . . . . . . : Microsoft Loopback Adapter
Physical Address. . . . . . . . . : 02-00-4C-4F-4F-50
Install Microsoft loopback adapter.
If the loopback adapter is not installed, with Administrator authority, start the "Add Hardware wizard" by entering the command: hdwwiz.exe
If prompted for permission to run the program, select "Yes".
When the Welcome screen is displayed, select "Next".
Select "Install the hardware that I manually select from a list" and select "Next"
Select "Network adapters" and select "Next".
In the "Manufacturer" (left) box, select "Microsoft". Near the end of the "Model" (right) box, select "Microsoft KM-TEST Loopback Adapter" or "Microsoft Loopback Adapter". Select "Next".
Select "Next".
Select "Finish". A reboot is necessary after the installation completes.
Add cluster alias to loopback adapter.
From the "Network Connections" screen, right-click the loopback adapter and select "Properties".
Select "Internet Protocol Version 4 (TCP/IPv4)" to add an IPv4 address or "Internet Protocol Version 6 (TCP/IPv6)" to add an IPv6 address. Select "Properties".
Select "Use the following IP address".
By default, the loopback interface has "Obtain an IP address automatically" selected. In order to assign more than one address to the interface, a static address must be assigned. If there is only a single cluster address that needs to be configured, the interface can be modified to use the cluster address as the static address.
Enter the cluster address in the IP address field and enter 255.255.255.255 as the subnet mask.
If multiple addresses are necessary on the interface, select the "Advanced" button on the previous "Advanced TCP/IP Settings". Select "Add" to add more addresses. The subnet mask must be 255.255.255.255 for all load balancer clusters.
Add cluster alias to loopback adapter by using the command line.
- To determine the interface name of the loopback adapter, issue "ipconfig /all" from a command prompt. Locate the entry with a description of "loopback adapter". Note the interface name displayed for the loopback adapter.
Ethernet adapter Local Area Connection 2:
Description ...Microsoft Loopback Adapter
The interface name is "Local Area Connection 2" in the example. - Alias the cluster address to the loopback:
netsh interface ipv4 add address "Local Area Connection 2" <cluster_ip_address> 255.255.255.255
Set loopback interface options:
The interface settings forwarding, weakhostreceive and weakhostsend must be enabled.
Determine the interface names to use with netsh with the command:
C:\Users\Administrator>netsh interface show interface
Admin State State Type Interface Name
-------------------------------------------------------------------------
Enabled Connected Dedicated Ethernet
Enabled Connected Dedicated Ethernet 2
Enabled Connected Dedicated Ethernet 3
Disabled Disconnected Dedicated Ethernet 4
Forwarding:
Display the current forwarding setting:
C:\Users\Administrator>netsh interface ipv4 dump
# ----------------------------------
# IPv4 Configuration
# ----------------------------------
pushd interface ipv4
reset
set global icmpredirects=enabled
add route prefix=0.0.0.0/0 interface="Ethernet 3" nexthop=169.254.144.61 publish=Yes
set interface interface="Local Area Connection* 1" forwarding=enabled advertise=enabled nud=enabled ignoredefaultroutes=disabled
set interface interface="Ethernet" forwarding=disabled advertise=enabled nud=enabled ignoredefaultroutes=disabled
set interface interface="Ethernet 2" forwarding=enabled advertise=enabled nud=enabled ignoredefaultroutes=disabled
set interface interface="Ethernet 3" forwarding=disabled advertise=enabled nud=enabled ignoredefaultroutes=disabled
set interface interface="Ethernet 4" forwarding=enabled advertise=enabled nud=enabled ignoredefaultroutes=disabled
add address name="Ethernet 3" address=1.2.3.4 mask=255.255.255.255
Enable forwarding for all of the interfaces on the machine.
Elevated administrator privileges are required to modify forwarding.
netsh interface ipv4 set interface "Ethernet" forwarding=enabled
netsh interface ipv4 set interface "Ethernet 3" forwarding=enabled
An "OK" message is displayed after a successful change.
Weakhost settings:
By default, the weakhostreceive and weakhostsend settings are disabled.
Display the current settings:
C:\Users\Administrator>powershell -command "Get-NetIPInterface | ft interfacealias,weakhostreceive,weakhostsend"
interfacealias WeakHostReceive WeakHostSend
-------------- --------------- ------------
Loopback Pseudo-Interface 1 Disabled Disabled
Ethernet 3 Disabled Disabled
Ethernet 2 Disabled Disabled
Ethernet Disabled Disabled
Loopback Pseudo-Interface 1 Disabled Disabled
Enable weakhost settings for all of the interfaces on the machine.
Elevated administrator privileges are required to modify forwarding
C:\Windows\system32>powershell -command "Set-NetIPInterface -WeakHostReceive enabled -WeakHostSend enabled"
Firewall settings:
If the Load Balancer indicates packets forwarded to the server but the server does not indicate any receiving the requests, disable the firewall software and retry requests. The Load Balancer forwarding statistics for a server are displayed with the command: dscontrol server report <cluster>@<port>@<server>
If the Load Balancer indicates packets forwarded to the server, collect a network trace at the server spanning a period where traffic is forwarded to the server by the Load Balancer. If the network trace does not capture packets with a destination IP address of the cluster address, examine network infrastructure such as switches to determine the cause of the problem. If the network trace captures packets with the cluster address as the destination IP address, the local operating system is discarding the traffic. Search for running firewall process and increase logging of firewall software to determine the problem.
References to assist with firewall investigation:
[{"Product":{"code":"SSEQTP","label":"WebSphere Application Server"},"Business Unit":{"code":"BU059","label":"IBM Software w\/o TPS"},"Component":"Edge Component","Platform":[{"code":"PF033","label":"Windows"}],"Version":"8.5.5;8.5;8.0;7.0","Edition":"Edition Independent","Line of Business":{"code":"LOB45","label":"Automation"}}]
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Document Information
Modified date:
09 December 2021
UID
swg21304795