IBM Support

Network trace compatibility issues with the Load Balancer for IPv4 and IPv6.



Network trace cannot run concurrently with the Load Balancer for IPv4 and IPv6 unless the load balancer's configuration is modified.


The Load Balancer for IPv4 and IPv6 and network trace tools (iptrace or tcpdump) all use the same AIX® resource to capture ARP packets (the ns_tap filter). The filter allows a single resource so the network trace tool and the Load Balancer cannot both function concurrently with the default configuration.

With default settings, when the Load Balancer and a network trace tool are both active, any of these problems can be observed:

  • The trace tool displays the message "no suitable device found".
  • No errors are observed but only broadcast traffic is captured by the trace tool.
  • The Load Balancer does not receive traffic for the defined clusters.


The Load Balancer for IPv4 and IPv6 manages cluster advertising by using the ARP protocol that requires the load balancer to use the ns_tap filter. The ns_tap filter is required by network trace tools to capture all network traffic. The ns_tap filter allows a single resource.



Resolving The Problem

The Load Balancer for IPv4 and IPv6 added the ability to configure it so that it does not use the ns_tap filter and thus network trace tools can execute without impacting packet forwarding.

To use this special configuration, you must have fix pack levels or (or higher) installed.

1) If the load balancer is running, stop the executor and load balancer.

2) Modify the LB_PROMISCUOUS value. Edit the /opt/IBM/WebSphere/Edge/ULB/servers file/bin/lbexecutor.AIX file and modify the LB_PROMISCUOUS value.

A value of "0" is the default setting. The load balancer uses the ns_tap resource for ARP processing.

A value of "1" disables the load balancer ARP processing. All active addresses must be configured on the operating systems interfaces.

Note: The lbexecutor.AIX file is overwritten when fix packs are installed. To configure the setting to persist, create the file /opt/IBM/WebSphere/Edge/lbexecutor.conf and add the LB_PROMISCUOUS="1" line to the file.

***IMPORTANT*** - You must now configure the addresses in order for traffic to be forwarded (the load balancer no longer send ARP packets so the addresses must be configured on the operating system).

3) If you are running in a high availability environment, you need to configure the clusters in the goActive script and unconfigure the clusters in the goStandby and goInOp scripts. Information about go scripts is provided in the Administrators guide.

If you are running in a stand-alone environment (no high availability), add "dscontrol executor configure <address>" for each cluster into the load balancer configuration file or issue the commands after the clusters are defined. If a server in the cluster is defined for NAT forwarding, the return address is configured by the Load Balancer when the cluster is configured.

You can run network trace software at any time during or after this configuration. The lbexecutor.AIX file is overwritten when fix packs are installed so document this configuration step in your process.

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Document Information

Modified date:
19 April 2023