Intermittent network connectivity issues with Chassis Management Module (CMM) or Advanced Management Module (AMM) - IBM BladeCenter and Flex Systems

Resolving The Problem

Source

RETAIN tip: H212565

Symptom

Intermittent network connectivity issues on a Chassis Management Module (CMM) or Advanced Management Module (AMM) that has not been accessed within the last five minutes.

For example:

A ping to a CMM or AMM returns:

This error occurs when both these conditions are met:

• The time between ping attempts is greater than 300 seconds.
• The device issuing the ping to the CMM or AMM has an Address Resolution Protocol (ARP) entry that lasts more than 300 seconds, such as a static ARP entry.

Refer to the Additional Information section for more information on how the CMM or AMM switch functions.

Affected Configurations

The system is configured with one or more of the following IBM option part numbers:

• BladeCenter Advanced Management Module, option part number 25R5778, any replacement part number
• Flex System Chassis Management Module, option part number 68Y7029, any replacement part number

This tip is not system specific.

This tip is not software specific.

Workaround

There are two alternative methods to prevent this scenario from happening:

1. Ping or connect to the CMM or AMM with an interval of less than five minutes.
2. Use an ARP cache timeout value less than or equal to five minutes on the host machine.

Additional Information

The L2 switch on the CMM or AMM blocks any unicast packets that are destined for an unknown MAC address. This includes the Internet Protocol (IP) interface of the CMM or AMM itself. So if the IP interface of the CMM or AMM has not been reached in more than five minutes, the L2 switch purges its entry and blocks any ping requests that are sent as a unicast packet.

If the host that issues the ping does not have a static ARP entry or long ARP cache timeout value, the host send a normal ping. A normal ping includes includes an ARP broadcast, and therefore the CMM or AMM replies as expected.