55
As shown in
{
Device A and Device B are directly connected.
{
GigabitEthernet 3/1/1 on Device A and GigabitEthernet 3/1/1 on Device B allow the traffic
of VLAN 1 to pass through. GigabitEthernet 3/1/2 on Device A and GigabitEthernet 3/1/2
on Device B allow the traffic of VLAN 2 to pass through.
{
Device A is the root bridge, and Device A and Device B both run a spanning tree protocol.
GigabitEthernet 3/1/2 on Device B is blocked, causing traffic of VLAN 2 to be blocked.
Configure VLAN Ignore to keep GigabitEthernet 3/1/2 of Device B in the forwarding state.
Figure 16
Network diagram
2.
Configuration procedure
# Enable VLAN Ignore for VLAN 2 on Device B.
<DeviceB> system-view
[DeviceB] stp ignored vlan 2
# 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 MST
region-related configurations (region name, revision level, VLAN-to-instance mappings) on them are
identical. A spanning tree device identifies devices in the same MST region by 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-instance mappings.
Spanning tree implementations vary with vendors, and the configuration digests calculated using private
keys is different. As a result, devices of different vendors in the same MST region cannot communicate
with each other.
To enable communication between an H3C router and a third-party device, enable the Digest Snooping
feature on the port connecting the H3C router to the third-party device in the same MST region.
NOTE:
Before enabling Digest Snooping, make sure that associated devices of different vendors are connected
and run spanning tree protocols.
GE3/1/1
Device A
Device B
VLAN 1
VLAN 2
GE3/1/2
GE3/1/1
GE3/1/2
Root port
Designated port
Normal link
Blocked link
Blocked port
Root
bridge