4000 Router Series Layer 2 - LAN Switching Configuration Guide

NOTE:

n mCheck operation takes effect on a device that operates in MSTP or RSTP mode.

Configuring Digest Snooping

As defined in IEEE 802.1s, connected devices are in the same region only when their MST region-related

configurations (region name, revision level, and VLAN-to-instance mappings) are identical. A spanning

tree device identifies devices in the same MST region by determining the configuration ID in BPDU

packets. The configuration ID includes the region name, revision level, and configuration digest, which is

16-byte long and is the result calculated through the HMAC-MD5 algorithm based on VLAN-to-instance

mappings.

Because spanning tree implementations vary by vendor, the configuration digests calculated through

private keys are different. The devices of different vendors in the same MST region cannot communicate

with each other.

To enable communication between an HP device and a third-party device, enable the Digest Snooping

feature on the port that connects the HP device to the third-party device in the same MST region.

Configuration restrictions and guidelines

When you configure Digest Snooping, follow these guidelines:

• Before you enable Digest Snooping, make sure associated devices of different vendors are

connected and run spanning tree protocols.

• With digest snooping enabled, in-the-same-region verification does not require comparison of

configuration digest, so the VLAN-to-instance mappings must be the same on associated ports.

• With digest snooping enabled globally, modify the VLAN-to-instance mappings or execute the

undo stp region-configuration command to restore the default MST region configuration with

caution. If the local device has different VLAN-to-instance mappings than its neighboring devices,

loops or traffic interruption occurs.

• To make Digest Snooping take effect, you must enable Digest Snooping both globally and on

associated ports. HP recommends that you enable Digest Snooping on all associated ports first and

then enable it globally. This will make the configuration take effect on all configured ports and

reduce impact on the network.

• To prevent loops, do not enable Digest Snooping on MST region edge ports.

• HP recommends that you enable Digest Snooping first and then the spanning tree feature. To avoid

traffic interruption, do not configure Digest Snooping when the network is already working well.

Configuration procedure

You can enable Digest Snooping only on the HP device that is connected to a third-party device that uses

its private key to calculate the configuration digest.

To configure Digest Snooping:

Ste

Command

Remarks

1. Enter system view.

system-view N/A