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Configuration Example
Network requirements
z
Device A and Device B are directly connected;
z
GigabitEthernet 1/0/1 on Device A and GigabitEthernet 1/0/1 on Device B allow the traffic of VLAN
1 to pass through. GigabitEthernet 1/0/2 on Device A and GigabitEthernet 1/0/2 on Device B allow
the traffic of VLAN 2 to pass through.
z
Device A is the root bridge, and both Device A and Device B run MSTP. GigabitEthernet 1/0/2 on
Device B is blocked, causing traffic block on VLAN 2.
z
Configure VLAN Ignore to make the blocked port forward packets.
Figure 1-7
VLAN Ignore configuration
GE1/0/1
Device A
Device B
VLAN 1
VLAN 2
GE1/0/2
GE1/0/2
GE1/0/1
Configuration procedure
1) Enable VLAN Ignore on Device B
# Enable VLAN Ignore on VLAN 2.
<DeviceB> system-view
[DeviceB] stp ignored vlan 2
2) Verify the configuration
# Display the VLAN Ignore enabled VLAN.
[DeviceB] display stp ignored-vlan
STP-Ignored VLAN: 2
Configuring Digest Snooping
As defined in IEEE 802.1s, interconnected devices are in the same region only when the region-related
configuration (domain name, revision level, VLAN-to-MSTI mappings) on them is identical. An MSTP
enabled device identifies devices in the same MST region via checking the configuration ID in BPDU
packets. The configuration ID includes the region name, revision level, configuration digest that is in
16-byte length and is the result calculated via the HMAC-MD5 algorithm based on VLAN-to-MSTI
mappings.
Since MSTP implementations differ with vendors, the configuration digests calculated using private
keys is different; hence different vendors’ devices in the same MST region can not communicate with
each other.
Enabling the Digest Snooping feature on the port connecting the local device to another vendor’s device
in the same MST region can make the two devices communicate with each other.
