Configuring Digest Snooping; Configuration Restrictions And Guidelines - HP FlexFabric 12900 Series Configuration Manual

Step
2. Enter Layer 2 Ethernet or aggregate interface
view.
3. Perform mCheck.

Configuring Digest Snooping

CAUTION:
Use caution with global Digest Snooping in the following situations:
• When you modify the VLAN-to-instance mappings.
When you restore the default MST region configuration.
•
If the local device has different VLAN-to-instance mappings than its neighboring devices, loops or traffic
interruption will occurs.
As defined in IEEE 802.1s, connected devices are in the same region only when they have the same MST
region-related configurations, including:
Region name.
•
Revision level.
•
VLAN-to-instance mappings.
•
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. It
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 in the same MST region,
enable Digest Snooping on the HP device port connecting them.

Configuration restrictions and guidelines

When you configure Digest Snooping, follow these restrictions and 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. The VLAN-to-instance mappings must be the same on associated ports.
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.
Command
interface interface-type interface-number
stp mcheck
100