89
•
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 H3C device and a third-party device in the same MST region,
enable Digest Snooping on the H3C device port connecting them.
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. 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. As a best practice, 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.
•
As a best practice, 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
Use this feature on when your H3C device is connected to a third-party device that uses its private
key to calculate the configuration digest.
To configure Digest Snooping:
Step Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter Layer 2 Ethernet or
aggregate interface view.
interface interface-type
interface-number
N/A
3.
Enable Digest Snooping on
the interface.
stp config-digest-snooping
By default, Digest Snooping is
disabled on ports.
4.
Return to system view.
quit
N/A
5.
Enable Digest Snooping
globally.
stp global
config-digest-snooping
By default, Digest Snooping is
disabled globally.
Summary of Contents for H3C S7500E-X
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