3Com Switch 4800G 24-Port - Page 111

Introduction to GVRP 111
GARP participants send protocol data units (PDU) with a particular multicast MAC
address as destination. Based on this address, a device can identify to which GVRP
application, GVRP for example, should a GARP PDU be delivered.
GARP message format
The following figure illustrates the GARP message format.
Figure 31 GARP message format
Table 25 describes the GARP message fields.
Table 25 Description on the GARP message fields
Field Description Value
Protocol ID Protocol identifier for GARP 1
Message One or multiple messages, each
containing an attribute type and an
attribute list
--
Attribute Type Defined by the concerned GARP
application
0x01 for GVRP, indicating the VLAN
ID attribute
Attribute List Contains one or multiple attributes --
Attribute Consists of an Attribute Length, an
Attribute Event, and an Attribute
Value
--
Attribute Length Number of octets occupied by an
attribute, inclusive of the attribute
length field
2 to 255 (in bytes)
Attribute Event Event described by the attribute 0: LeaveAll event
1: JoinEmpty event
2: JoinIn event
3: LeaveEmpty event
4: LeaveIn event
5: Empty event
GARP PDU structure
Message structure
Attribute List structure
Attribute structure
Protocol ID Message N End Mark...
Attribute 1 End Mark...
Attribute Type
Attribute Length Attribute Event Attribute Vlaue
1
1
1
1
3
3
2
2
N
N
N
N
Message 1
Attribute List
Attribute N
PDUDA length DSAPDA CtrlSSAP Ethernet Frame