1-35Configuration ExampleNetwork requirementsz 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 VLAN1 to pass through. GigabitEthernet 1/0/2 on Device A and GigabitEthernet 1/0/2 on Device B allowthe 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 onDevice 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 configurationGE1/0/1Device A Device BVLAN 1VLAN 2GE1/0/2 GE1/0/2GE1/0/1Configuration procedure1) Enable VLAN Ignore on Device B# Enable VLAN Ignore on VLAN 2. system-view[DeviceB] stp ignored vlan 22) Verify the configuration# Display the VLAN Ignore enabled VLAN.[DeviceB] display stp ignored-vlanSTP-Ignored VLAN: 2Configuring Digest SnoopingAs defined in IEEE 802.1s, interconnected devices are in the same region only when the region-relatedconfiguration (domain name, revision level, VLAN-to-MSTI mappings) on them is identical. An MSTPenabled device identifies devices in the same MST region via checking the configuration ID in BPDUpackets. The configuration ID includes the region name, revision level, configuration digest that is in16-byte length and is the result calculated via the HMAC-MD5 algorithm based on VLAN-to-MSTImappings.Since MSTP implementations differ with vendors, the configuration digests calculated using privatekeys is different; hence different vendors’ devices in the same MST region can not communicate witheach other.Enabling the Digest Snooping feature on the port connecting the local device to another vendor’s devicein the same MST region can make the two devices communicate with each other.
