Serviceguard Network Manager: Inbound Failure Detection, March 2007

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Serviceguard Network Manager

Introduction......................................................................................................................................... 2

Serviceguard Network Manager—default network failure detection mechanism .......................................... 2

Driver error notification..................................................................................................................... 2

Traffic statistics and polling mechanism............................................................................................... 2

Inbound failure detection enhancement .................................................................................................. 3

Why the enhancement was made ...................................................................................................... 3

Configuration of network failure detection........................................................................................... 4

How inbound failure detection works.................................................................................................. 4

Handling a broken cascaded cable................................................................................................ 4

Algorithm for inbound failure detection method................................................................................ 5

Risks associated with INONLY_OR_INOUT ..................................................................................... 6

Examples of network configurations with risks .................................................................................. 6

Guidelines and recommendation.................................................................................................... 8

For more information............................................................................................................................ 9

Summary of content (9 pages)

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Serviceguard Network Manager Introduction......................................................................................................................................... 2 Serviceguard Network Manager—default network failure detection mechanism .......................................... 2 Driver error notification..................................................................................................................... 2 Traffic statistics and polling mechanism...........................
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Introduction This white paper provides a brief description about the default behavior of the Serviceguard network failure detection mechanism. It also describes the network failure detection mechanism that deals with inbound-only failures. It further explains the conditions under which the INONLY setting should be applied.
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Figure 1. Typical network configuration for a two-node cluster The default method has been the only method of network failure detection (INOUT) provided by Serviceguard before version A.11.16. With this default method, Serviceguard will mark a NIC as failed only if both inbound and outbound statistics of a NIC stop incrementing for a set amount of time, which guards against transient failures..
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Configuration of network failure detection The network failure detection method is configurable. Users can choose between the existing default method of INOUT or the new enhanced method of INONLY_OR_INOUT. Changes to this parameter can be made online without having to bring the cluster down. The network failure detection setting is modified in the cluster configuration file by setting the value for the NETWORK_FAILURE_DETECTION parameter.
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The primary and standby NICs, lan0 and lan1, send polling packets to each other through the cascading cable (see Figure 2). Assume that the cascading cable gets disconnected. Now each NIC can send but cannot receive any poll packets. There is no other incoming traffic that can increment the inbound statistics at the time. Using the default setting of INOUT, Serviceguard Network Manager detects the failure. However, Serviceguard Network Manager takes no action and logs no errors.
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2. Serviceguard Network Manager starts polling from the problem NIC to all other NICs on the same bridged network in entire the cluster. This is known as “full polling.” 3. If the NIC gets a response from any peer NIC, then the NIC with the initial problem is considered healthy and there is no need for a failover. This situation can happen in the broken cascaded cable example shown in Figure 3. 4.
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Figure 4. Single point of failure Example 2: Another case of broken cascaded cable in a two-node cluster with only one NIC in each cluster member and no standby where each NIC connects to a switch. The two switches are connected by a cascading cable. These switches connect to routers and then to the client LAN. If the cascading cable breaks, each NIC can send poll messages but neither can receive them. The INONLY_OR_INOUT setting will identify both NICs as failed and the cluster health as fine.
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in each node, the two NICs remotely poll each other. If the NIC in Node B fails and is identified as failed, and there is no traffic other than the remote polling traffic that just stopped, the inbound statistics of lan0 on node A will not be incrementing. Using the INONLY_OR_INOUT setting, Serviceguard Network Manager running on node A will declare lan0 on Node A down— the whole subnet will be down. In this situation the default setting of INOUT would be a better choice.
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For more information To learn more about HP high-availability products and solutions, please visit: www.hp.com/go/serviceguard HP Partitioning Continuum, HP, 2006 HP ENSAextended technical overview, HP, 2006 HP Utility Data Center Overview, HP, 2006 © 2006 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice. The only warranties for HP products and services are set forth in the express warranty statements accompanying such products and services.