Information About IEEE 802.1ak MVRP and MRP
The IEEE 802.1ak Multiple VLAN Registration Protocol (MVRP) supports dynamic registration and deregistration of VLANs on ports in a VLAN bridged network. IEEE 802.1ak uses more efficient Protocol Data Units (PDUs) and protocol design to provide better performance than the Generic VLAN Registration Protocol (GARP) VLAN Registration Protocol (GVRP) and GARP Multicast Registration Protocol (GMRP) protocols.
A VLAN-bridged network usually restricts unknown unicast, multicast, and broadcast traffic to those links that the traffic uses to access the appropriate network devices. In a large network, localized topology changes can affect the service over a much larger portion of the network. IEEE 802.1ak replaces GARP with the Multiple Registration Protocol (MRP), which provides improved resource utilization and bandwidth conservation.
With the 802.1ak MRP attribute encoding scheme, MVRP only needs to send one PDU that includes the state of all 4094 VLANs on a port. MVRP also transmits Topology Change Notifications (TCNs) for individual VLANs. This is an important feature for service providers because it allows them to localize topology changes. Figure 21-1 illustrates MVRP deployed in a provider network on provider and customer bridges.
Figure 21-1 MVRP Deployed on Provider and Customer Bridges
Because most providers do not wish to filter traffic by destination MAC addresses, a pruning protocol like MVRP is important in a Metro Ethernet provider network, which often uses thousands of VLANs.
Figure 21-2 dispalys redundant links that are configured between the access switch and two distribution switches on the cloud. When the link with VLAN 104 fails over, MVRP needs to send only one TCN for VLAN 104. Without MVRP, an STP TCN would need to be sent out for the whole MST region (VLANs1-1000), which could cause unnecessary network interruption.
STP sets the tcDetected variable to signal MVRP that MVRP must decide whether to send an MVRP TCN. MVRP can flush filtering database entries rapidly on a per-VLAN basis following a topology change because when a port receives an attribute declaration marked as new, any entries in the filtering database for that port and for that VLAN are removed.
Figure 21-2 MVRP TCN Application
Dynamic VLAN Creation
Virtual Trunking Protocol (VTP) is a Cisco proprietary protocol that distributes VLAN configuration information across multiple devices within a VTP domain. When VTP is running on MVRP-aware devices, all of the VLANs allowed on the Cisco bridged LAN segments are determined by VTP.
Only the VTP transparent mode supports MVRP dynamic VLAN creation. When dynamic VLAN creation is disabled, the MVRP trunk ports can register and propagate the VLAN messages only for existing VLANs. MVRP PDUs and MVRP messages for the nonexistant VLANs are discarded.
For a switch to be configured in full compliance with the MVRP standard, the switch VTP mode must be transparent and MVRP dynamic VLAN creation must be enabled.
MVRP Interoperability with VTP
The VLAN Trunking Protocol (VTP) is a Cisco proprietary protocol that distributes VLAN configuration information across multiple devices within a VTP domain. VTP pruning is an extension of VTP. It has its own Join message that can be exchanged with VTP PDUs. VTP PDUs can be transmitted on both 802.1Q trunks and ISL trunks. A VTP-capable device is in one of the VTP modes: server, client, transparent, or off.
When VTP Pruning and MVRP are both enabled globally, MVRP runs on trunks where it is enabled and VTP Pruning runs on other trunks. MVRP or VTP pruning can be enabled on a trunk, but not both.
VTP in Transparent or Off Mode
When VTP is in transparent or off mode, VTP pruning is not supported and VTP PDUs are not processed.
When a port receives an MVRP join message for a VLAN, the port transmits broadcast, multicast, and unknown unicast frames in that VLAN and adds the traffic definition to the MRP Attribute Propagation (MAP) port configured for that VLAN. The mapping is removed when the VLAN is no longer registered on the port.
For each interface that is forwarding in each VLAN, MVRP issues a join request to each MRP Attribute Declaration (MAD) instance and an MVRP Join message is sent out on each corresponding MVRP port.
MVRP dynamic VLAN creation can be enabled in VTP transparent or off mode. If it is enabled and the VLAN registered by a join message does not exist in the VLAN database in the device, then the VLAN will be created.
VTP in Server or Client Mode and VTP Pruning is Disabled
MVRP functions like VTP in transparent or off mode, except that MVRP dynamic VLAN creation is not allowed.
VTP in Server or Client Mode and VTP Pruning is Enabled
MVRP and VTP with pruning disabled can be supported on the same port and these two protocols need to communicate and exchange pruning information.
When VTP receives a VTP join message on a VTP trunk, MVRP is notified so that join request can be posted to the MVRP port MAD instances, and MVRP join messages are out on the MVRP ports to the MVRP network.
When VTP pruning removes a VLAN from a VTP trunk, MVRP sends a leave request to all the MAD instances and the MAD instances send a leave or empty message from the MVRP ports to indicate that the VLAN is not configured on the device.
When an MVRP port received an MVRP join message, MVRP propagates the event to other MVRP ports in the same MAP context, and notifies VTP so that VTP pruning can send a VTP join message from the VTP trunk ports.
If MVRP learns that a VLAN is no longer declared by the neighboring devices, MVRP sends a withdrawal event to VTP and then VTP pruning verifies that it should continue sending VTP join messages.
For VLANs that are configured as VTP pruning non-eligible on the VTP trunks, the VTP pruning state variables are set to joined for the VLANs. MVRP join requests are sent to those VLANs through the MVRP ports.
MVRP Interoperation with Non-Cisco Devices
Non-Cisco devices can interoperate with a Cisco device only through 802.1q trunks.
MVRP Interoperability with Other Software Features and Protocols
802.1x and Port Security
802.1x authenticates and authorizes a port after it transitions to the link-up state, but before DTP negotiation occurs and MVRP runs on a port. Port security works independently of MVRP.
Note When MVRP is globally enabled, the MVRP MAC address auto detect and provision feature is disabled by default (mvrp mac-learning auto). In some situations, MVRP MAC address auto detect and provision can disable MAC address learning and prevent correct port security operation. For example, on ports where port security is configured, when the number of streams exceeds the configured maximum number of MAC addresses, no port security violation occurs because MAC address learning is disabled, which prevents updates to port security about the streams coming into the port. To avoid incorrect port security operation, use caution when enabling the MVRP MAC address auto detect and provision feature on ports where port security is configured.
DTP negotiation occurs after ports transition to the link-up state and before transition to the forwarding state. If MVRP is administratively enabled globally and enabled on a port, it becomes operational when the port starts trunking.
An EtherChannel port-channel interface can be configured as an MVRP participant. The EtherChannel member ports cannot be MVRP participants. MVRP learns the STP state of EtherChannel port-channel interfaces. The MAP context applies to the EtherChannel port-channel interfaces, but not to the EtherChannel member ports.
MVRP declares VLANs on STP forwarding ports but not on ports in the blocking state. On flex links ports, MVRP declares VLANs on the active ports but not on the standby ports. when a standby port takes over and an active port transitions to the link-down state, MVRP declares the VLANs on the newly active port.
State Switchover (SSO) and ISSU supports MVRP.
ISSU and eFSU
Enhanced Fast Software Upgrade (EFSU) is an enhanced software upgrade procedure. MVRP is serviced by the ISSU client identified as ISSU_MVRP_CLIENT_ID.
Layer 2 Protocol Tunneling (L2PT) does not support MVRP PDUs on 802.1Q tunnel ports.
MVRP ports can be configured as either Switched Port Analyzer (SPAN) sources or destinations.
Unknown Unicast and Multicast Flood Control
MVRP and the Unknown Unicast and Multicast Flood Control feature, configured with the switchport block command, cannot be configured on the same port.
An STP mode change causes forwarding ports to leave the forwarding state until STP reconverges in the newly configured mode. The reconvergence might cause an MVRP topology change because join messages might be received on different forwarding ports, and leave timers might expire on other ports.
MVRP and unidirectional link routing (UDLR) cannot be configured on the same port.
VLAN translation and MVRP cannot be configured on the same port.
802.1Q Native VLAN Tagging
Other MVRP participants might not be able to accept tagged MVRP PDUs in the 802.1Q native VLAN. Compatibility between MVRP and 802.1Q native VLAN tagging depends on the specific network configuration.
Private VLAN ports cannot support MVRP.