QTECH
Software Configuration Manual
5-70
for VLAN aware switches, which requires IEEE 802.1Q.
Generic Attribute Registration Protocol (GARP) provides a mechanism that allows participants in a GARP
application to distribute, propagate, and register with other participants in a bridged LAN the attributes specific to the
GARP application, such as the VLAN or multicast address attribute.
GARP itself does not exist on a device as an entity. GARP-compliant application entities are called GARP
applications. One example is GVRP. When a GARP application entity is present on a port on your device, this port is
regarded a GARP application entity.
5.3.2
Brief introduction of GVRP
Multiple VLAN Registration Protocol
(
MVRP
) formerly known as
GARP VLAN Registration
Protocol
(
GVRP
) is a standards-based Layer 2 network protocol, for automatic configuration of VLAN information
on switches. It was defined in the 802.1ak amendment to 802.1Q-2005.
Within a layer 2 network, MVRP provides a method to dynamically share VLAN information and
configure the needed VLANs. For example, in order to add a switch port to a VLAN, only the end port, or the
VLAN-supporting network device connected to the switchport, need be reconfigured, and all necessary VLAN trunks
are dynamically created on the other MVRP-enabled switches. Without MVRP, (or the similar Cisco-proprietary
protocol VTP) manual configuration of VLAN trunks is necessary.
It is through MVRP that Dynamic VLAN entries will be updated in the Filtering Database. In short, MVRP
helps to maintain VLAN configuration dynamically based on current network configurations.
802.1Q allows for :
1.
Dynamic configuration and distribution of VLAN membership information by means of the MVRP
2.
Static configuration of VLAN membership information via Management mechanisms, which allow
configuration of Static VLAN Registration Entries.
3.
Combined static and dynamic configuration, in which some VLANs are configured via Management
mechanisms and for other VLANs, MVRP is relied on to establish the configuration.
5.3.3
GARP messages and timers
1) GARP messages
GARP participants exchange attributes primarily by sending the following three types of messages :
·
Join to announce the willingness to register some attribute with other participants.
·
Leave to announce the willingness to deregister with other participants. Together with Join
messages, Leave messages help GARP participants complete attribute reregistration and
deregistration.
·
LeaveAll to deregister all attributes. A LeaveAll message is sent upon expiration of a LeaveAll
timer, which starts upon the startup of a GARP application entity.
·
Through message exchange, all attribute information that needs registration propagates to all GARP
participants throughout a bridged LAN.
2) GARP timers
GARP sets interval for sending GARP messages by using these four timers :
·
Hold timer –– When a GARP application entity receives the first registration request, it starts a
hold timer and collects succeeding requests. When the timer expires, the entity sends all these requests in one
Join message. This can thus help you save bandwidth.
·
Join timer –– Each GARP application entity sends a Join message twice for reliability sake and
uses a join timer to set the sending interval.
·
Leave timer –– Starts upon receipt of a Leave message sent for deregistering some attribute
information. If no Join message is received before this timer expires, the GARP application entity removes
the attribute information as requested.
·
LeaveAll timer –– Starts when a GARP application entity starts. When this timer expires, the
entity sends a LeaveAll message so that other entities can re-register its attribute information. Then, a
LeaveAll timer starts again.
