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Understanding Multiple VLAN Registration Protocol (MVRP) on EX Series Switches

How MVRP Updates, Creates, and Deletes VLANs on the Switches

When any MVRP-member VLAN is changed, that VLAN sends a protocol data unit (PDU) to all other MVRP-member active VLANs. The PDU informs the other VLANs which switches and interfaces currently belong to the sending VLAN. This way, all MVRP-member VLANs are always updated with the current VLAN state of all other MVRP-member VLANs. Timers dictate when PDUs can be sent and when switches receiving MVRP PDUs can update their MVRP VLAN information.

In addition to sending PDU updates, MVRP dynamically creates VLANs on member interfaces when a new VLAN is added to any one interface. This way, VLANs created on one member switch are propagated to other member switches as part of the MVRP message exchange process.

To keep VLAN membership information current, MVRP removes switches and interfaces when they become unavailable. Pruning VLAN information has these benefits:

• Limits the network VLAN configuration to active participants, thereby reducing network overhead.
• Limits broadcast, unknown unicast, and multicast (BUM) traffic to interested devices.

MVRP Is Disabled by Default on the Switches

MVRP is disabled by default on the switches and, when enabled, affects only trunk interfaces. Once you enable MVRP, all VLAN interfaces on the switch belong to MVRP (the default normal registration mode) and those interfaces accept PDU messages and send their own PDU messages. To prevent one or more interfaces from participating in MVRP, you can specifically configure an interface to forbidden registration mode instead of the default normal mode.

VLAN updating, dynamic VLAN configuration through MVRP, and VLAN pruning are all active on trunk interfaces when MVRP is enabled.

MRP Timers Control MVRP Updates

MVRP registration and updates are controlled by timers that are part of the MRP. The timers define when MVRP PDUs can be sent and when MVRP information can be updated on a switch.

The timers are set on a per-interface basis, and on EX Series switches that use Juniper Networks Junos operating system (Junos OS) with support for the Enhanced Layer 2 Software (ELS) configuration style, the timers are also set on a per-switch basis.

On an EX Series switch that uses Junos OS with support for ELS, if the timer value set on an interface level is different from the value set on a switch level, the value on the interface level takes precedence.

The following MRP timers are used to control the operation of MVRP:

• Join timer—Controls the interval for the next MVRP PDU transmit opportunity.
• Leave timer—Controls the period of time that an interface on the switch waits in the leave state before changing to the unregistered state.
• LeaveAll timer—Controls the frequency with which the interface generates LeaveAll messages.

Best Practice: Unless there is a compelling reason to change the timer settings, leave the default settings in place. Modifying timers to inappropriate values can cause an imbalance in the operation of MVRP.

MVRP Uses MRP Messages to Transmit Switch and VLAN States

MVRP uses MRP messages to register and declare MVRP states for a switch or VLAN and to inform the switching network that a switch or VLAN is leaving MVRP. These messages are communicated as part of the PDU sent by any switch interface to the other switches in the network.

The following MRP messages are communicated for MVRP:

• Empty—MVRP information is not declared and no VLAN is registered.
• In—MVRP information is not declared but a VLAN is registered.
• JoinEmpty—MVRP information is declared but no VLAN is registered.
• JoinIn—MVRP information is declared and a VLAN is registered.
• Leave—MVRP information that was previously declared is withdrawn.
• LeaveAll—Unregister all VLANs on the switch. VLANs must re-register to participate in MVRP.
• New—The MVRP information is new and a VLAN might not be registered yet.

Compatibility Issues with Junos OS Releases of MVRP

Except in Junos OS Releases 11.2 and earlier, MVRP has conformed with IEEE standard 802.1ak and IEEE Draft 802.1Q regarding the inclusion of an extra byte in the protocol data units (PDUs) sent and received by MVRP. Table 1 outlines the MVRP versions and whether or not each version includes the extra byte in the PDU. Table 1 also labels each MVRP version with a scenario number, which is used throughout the remainder of this discussion for brevity.

As a result of the non-conformance of Releases 11.2 and earlier and changes in the standards with regard to the extra byte, a compatibility issue exists between some of the Junos OS versions of MVRP. This issue can result in some versions of MVRP not recognizing PDUs without the extra byte.

To address this compatibility issue, the MVRP versions described in scenarios 2 and 3 include the ability to control whether or not the PDU includes the extra byte. Before using these controls, however, you must understand each scenario that applies to your environment and plan carefully so that you do not inadvertently create an additional compatibility issue between the MVRP versions in scenarios 2 and 3.

Table 2 provides a summary of environments that include the various MVRP scenarios and whether or not a particular environment requires you to take action.

You can determine whether the switches in your network are running incompatible versions of MVRP by issuing the show mvrp statistics command. For more information on diagnosing and correcting this MVRP compatibility situation, see Configuring Multiple VLAN Registration Protocol (MVRP) (CLI Procedure) or Configuring Multiple VLAN Registration Protocol (MVRP) (CLI Procedure ).