GVRP Technology White Paper

8/4/2019 GVRP Technology White Paper

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GVRP Technology White Paper

Hangzhou H3C Technologies Co.,Ltd. www.h3c.com /16

GVRP Technology White Paper Keywords: GARP, GVRP, attributes, registration, VLAN Abstract: GVRP is used to achieve dynamic VLAN configuration. This document introduces the

implementation and typical application of GVRP.

Acronyms: Acronym Full spelling

GARP Generic Attribute Registration ProtocolGMRP GARP Multicast Registration Protocol

GVRP GARP VLAN Registration Protocol

MSTP Multiple Spanning Tree Protocol




Hangzhou H3C Technologies Co.,Ltd. www.h3c.com /16

Table of Contents 1 Overview.........................................................................................................................................3

1.1 Background..........................................................................................................................3 1.2 Benefits ................................................................................................................................4

2 GVRP Implementation....................................................................................................................4 2.1 Concepts..............................................................................................................................4

2.1.1 GARP Application Participants..................................................................................4 2.1.2 VLAN Registration and Deregistration......................................................................4 2.1.3 Message Types .........................................................................................................5 2.1.4 Timers........................................................................................................................6 2.1.5 Registration Mode.....................................................................................................8

2.2 Packet Format......................................................................................................................8 2.3 Working Procedures ..........................................................................................................10 2.4 Restrictions ........................................................................................................................15

3 Application Scenarios ...................................................................................................................15 4 Prospect .......................................................................................................................................16 5 References ...................................................................................................................................16




Hangzhou H3C Technologies Co., Ltd. /16

1 Overview The Generic Attribute Registration Protocol (GARP) establishes an attributepropagation mechanism, which enables entities of a GARP application to register and

deregister certain attributes. You can use GARP to propagate attributes. By mapping

different attributes into the GARP protocol data unit (PDU), you can support different

upper-layer applications. GMRP and GVRP are two typical applications of GARP,

where,

GMRP is used to register and deregister multicast attributes.

GVRP is used to register and deregister VLAN attributes.

GARP applications are identified by destination MAC address. In IEEE Std 802.1D,

the destination MAC address 01-80-C2-00-00-20 is assigned to the multicast

application, that is, GMRP. In IEEE Std 802.1Q, the destination MAC address 01-80-

C2-00-00-21 is assigned to the VLAN application, that is, GVRP.

This white paper is focused on details relevant to GVRP.

1.1 Background Without GVRP, to configure a VLAN for each device in a network, you need to

manually configure it device by device. As shown in Figure 1 , VLAN 2 is configured

on Device A, while only VLAN 1 exists on Device B and Device C; the three devices

are interconnected through trunk links. To transmit traffic of VLAN 2 from Device A to

Device C, you need to manually create VLAN 2 on Device B and Device C.

Device A

Device B

Device C

Figure 1 GVRP application





In a simple network as shown in Figure 1 , it is easy to create VLANs manually. In a

complicated network, however, you can hardly get a complete view of the topology in

a short time or have to deal with a lot of VLANs. In either case, configuration errors

may result and heavy workload is involved. To address the problem, you can use the

automatic VLAN registration function of GVRP to complete VLAN configuration.

1.2 Benefits Based on GARP, GVRP is used to maintain dynamic VLAN attributes on devices.

With GVRP, a switch can exchange its VLAN configuration with other GVRP-aware

switches in the whole switched network. GVRP propagates, registers, and deregisters

VLAN attributes dynamically, reducing manual configuration workload and

guaranteeing VLAN configuration correctness.

2 GVRP Implementation 2.1 Concepts 2.1.1 GARP Application Participants

On a device, each port participating in a protocol is regarded as a participant of the

protocol. On a GVRP-enabled switch, each GVRP-enabled port is a GVRP participant,

as shown in Figure 2 .

GVRP participant

Figure 2 GVRP participant

2.1.2 VLAN Registration and Deregistration GVRP can register and deregister VLAN attributes automatically.





VLAN registration: assigns a port to a VLAN.

VLAN deregistration: removes a port from a VLAN.

GVRP registers and deregisters VLAN attributes automatically by making orwithdrawing declarations.

When a port receives a VLAN attribute declaration, the port registers the VLAN

information contained in the declaration, that is, joins the specified VLAN.

When a port receives a VLAN attribute withdrawal declaration, the port

deregisters the VLAN information contained in the declaration, that is, exits the

specified VLAN.

VLAN attribute registration or deregistration occurs only on ports receiving GVRP

PDUs.

Figure 3 VLAN registration and deregistration

2.1.3 Message Types GARP participants exchange attribute information by sending messages, which fall

into three types: join, leave, and LeaveAll.

1. Join message A GARP participant sends join messages to register with other entities as needed its

attributes, the attributes received from other GARP participants, and the attributes

manually configured on it.

Join messages fall into JoinEmpty messages and JoinIn messages, as described

below: JoinEmpty: Declares an attribute that is not configured on the local participant.

JoinIn: Declares an attribute that has already been registered with the local

participant.

2. Leave message

A GARP participant sends leave messages to have its attributes deregistered on





other devices. It also sends leave messages when it receives leave messages from

other GARP participants or when attributes are manually deregistered on it.

Leave messages fall into LeaveEmpty messages and LeaveIn messages, as

described below: LeaveEmpty: Deregisters an attribute that is not registered on the local

participant.

LeaveIn: Deregisters an attribute that has been registered on the local

participant.

3. LeaveAll message Upon startup, a GARP participant starts the LeaveAll timer. When the timer expires,

the GARP participant sends out a LeaveAll message.

A GARP participant sends LeaveAll messages to deregister all its attributes from all

the other GARP participants. This is a periodical garbage attribute clearing

mechanism used to clear attributes no longer useful. A garbage attribute may be

created when a device fails to send a leave message, because of power failure for

example, to notify other devices to deregister an attribute that it has removed.

2.1.4 Timers GARP uses four timers to set the interval for sending GARP messages.

1. Join timer The Join timer specifies the interval for sending join messages (including JoinIn and

JoinEmpty messages).

To guarantee join message transmission reliability, a GARP participant may send a join message twice. When sending the first join message, the GARP participant starts

the Join timer. If a JoinIn message is received before the Join timer expires, the

GARP participant does not send the second join message. If not, the GARP

participant re-sends the join message.

The Join timer is configured on a per-port basis.





2. Hold timer The Hold timer specifies the interval for sending join messages (including JoinIn and

JoinEmpty messages) and leave messages (including LeaveIn and LeaveEmpty

messages).

When you configure an attribute on a participant or when the participant receives a

request message, the participant does not propagate the message to the other

devices immediately. Instead, it collects the request messages received within a

period of time and sends them in one GARP PDU. This period of time is specified by

the Hold timer. By making full use of the data portion of GARP PDUs to send multiple

messages in one packet, the mechanism reduces the number of transmitted packetsand contributes to network stability.

The Holder timer is configured on a per-port basis. The Holder timer value must be no

greater than half the Join timer value.

3. Leave timer The Leave timer controls attribute deregistration.

Upon receiving a leave or LeaveAll message, a GARP participant starts its Leavetimer. If it receives no join message containing the attribute carried in the leave or

LeaveAll message when the Leave timer expires, it deregisters the attribute. The

Leave timer is used because the leave message from a GARP participant does not

mean that the attribute carried in the leave message has been removed from all other

GARP participants. Before deregistering the attribute carried in a received leave

message, the receiving GARP participant must wait for a while to make sure that the

attribute has been removed from all the GARP participants. For example, an attribute

is configured on GARP participants A and B in the network, and the other participants

have registered the attribute through the GARP application. When the attribute is

removed from participant A, participant A sends out a leave message. Upon receiving

the leave message, participant B, which still has the source of the attribute, sends out

a join message to indicate that it still has the attribute. Receiving the join message

from participant B, the other GARP participants keep the attribute instead of

deregistering it. Only if no join messages containing the attribute are received when

the time twice the Join timer is reached, will they consider that this attribute does not

exist in the network. Considering this, you must set the Leave timer to be greater than

twice the Join timer value.

The Leave timer is configured on a per-port basis.





4. LeaveAll timer Upon startup, a GARP participant starts the LeaveAll timer. When the LeaveAll timer

expires, the GARP participant sends out a LeaveAll message, and then restarts the

LeaveAll timer to start another cycle.

Once receiving a LeaveAll message, a GARP participant re-starts all timers, including

the LeaveAll timer. When its own LeaveAll timer expires, the participant sends out a

LeaveAll message, thus avoiding sending too many LeaveAll messages within a short

time.

If the LeaveAll timers of multiple devices expire at the same time, multiple LeaveAll

messages will be sent at the same time, creating unnecessary traffic. To avoid this

problem, the actual LeaveAll timer value of a participant is a random value between

the LeaveAll timer value and the LeaveAll timer value multiplied by 1.5.

A LeaveAll event is equivalent to deregistering all attributes network wide by sending

leave messages. Because the LeaveAll timer affects the whole network, you are

recommended to configure the LeaveAll timer value to be at least greater than the

Leave timer.

The LeaveAll timer is configured globally on a per-device basis.

2.1.5 Registration Mode A VLAN configured manually is referred to as a static VLAN, while a VLAN created

through GVRP is referred to as a dynamic VLAN. GVRP provides three registration

modes, which handle static VLANs and dynamic VLANs differently as follows:

Normal: In this mode, a port can dynamically register and deregister VLANs,

and propagate both dynamic and static VLAN declarations. Fixed: In this mode, a port cannot dynamically register VLANs, but it can

propagate static VLAN declarations.

Forbidden: In this mode, a port can neither dynamically register VLANs, nor

propagate declarations about any VLAN but VLAN 1.

2.2 Packet Format As shown in Figure 4 , a GARP protocol data unit (PDU) is encapsulated in an IEEE





802.3 Ethernet frame.

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 Value

1

1

1

1

3

3

2

2

N

N

N

N

Message 1

Attribute List

Attribute N

PDUDA length DSAPSA CtrlSSAP Ethernet Frame

Figure 4 GARP PDU format

Table 1 describes the fields of a GARP PDU.

Table 1 Description on the fields of a GARP PDU Field Description Value

Protocol ID Protocol identifier for GARP 1 Message

One or multiple messages,each containing an attributetype and attribute list —

Attribute TypeDefined by the specificGARP application 0x01 for GVRP, indicating

the VLAN ID attribute.

Attribute ListA list of one or multipleattributes —

AttributeConsisting of an AttributeLength, an Attribute Event,

and an Attribute Value —

Attribute LengthNumber of bytes occupiedby the attribute, including theAttribute Length field 2 bytes to 255 bytes

Attribute EventEvent described by theattribute

0: LeaveAll Event

1: JoinEmpty Event

2: JoinIn Event

3: LeaveEmpty Event

4: LeaveIn Event





Field Description Value

Attribute Value Value of the attribute VLAN ID for GVRP. If theAttribute Event is LeaveAll,the Attribute Value field is

invalid.

End MarkMark indicating the end of aGARP PDU.

0x00

2.3 Working Procedures This section describes how GVRP works using a simplified example. This example

describes how GVRP registers and deregisters VLAN attributes in four sub-sections.

1. Unidirectional VLAN attribute registration Device A

Device B

Device C

JoinEmpty

JoinEmpty

Static VLAN 2

Port 1

Port 2 Port 3

Port 4

Figure 5 Unidirectional VLAN attribute registration

Manually create static VLAN 2 on Device A. In response to this action, GVRP

automatically assigns the GVRP-enabled ports on Device B and Device C to VLAN 2

through unidirectional VLAN attribute registration as follows:





Upon manual creation of static VLAN 2 on Device A, Port 1 starts its Join timer

and Hold timer. When the Hold timer expires, Port 1 sends out the first

JoinEmpty message to Device B. When the Join timer expires, the Hold timer

restarts. When the Hold timer expires, Port 1 sends out the second JoinEmpty

message.

Upon receiving the first JoinEmpty message, Device B dynamically creates

VLAN 2, assigns the receiving port Port 2 to VLAN 2, and instructs Port 3 to

start its Join timer and Hold timer at the same time. When the Hold timer

expires, Port 3 sends out the first JoinEmpty message to Device C. When the

Join timer expires, the Hold timer restarts. When the Hold timer expires, Port 3

sends out the second JoinEmpty message. Upon receiving the second

JoinEmpty message from Device A, Device B does not perform any processing,

because Port 2 has already been assigned to VLAN 2.

Upon receiving the first JoinEmpty message, Device C dynamically creates

VLAN 2, and assigns the receiving port Port 4 to VLAN 2. Upon receiving the

second JoinEmpty message, Device C does not perform any processing,

because Port 4 has already been assigned to VLAN 2.

Thereafter, when the LeaveAll timer expires on a device or a LeaveAll message

is received on a device, the device restarts the LeaveAll timer, Join timers, Hold

timers, and Leave timers on it. Port 1 on Device A sends the first JoinEmpty

message when the Hold timer expires and sends the second JoinEmpty

message when the period of the Join timer value plus the Hold timer value is

reached. This process is true for Device B to send JoinEmpty messages to

Device C.

2. Bidirectional VLAN attribute registration Device A

Device B

Device C

JoinEmpty

JoinEmpty

Static VLAN 2

JoinIn

JoinIn

JoinIn

JoinIn

Static VLAN 2

Port 1

Port 2 Port 3

Port 4





Figure 6 Bidirectional VLAN attribute registration

The process described in Unidirectional VLAN attribute registration assigns to VLAN

2 Port 1, Port 2, and Port 4 but not Port 3, because only the port receiving a

JoinEmpty or JoinIn message can be dynamically assigned to a VLAN. To transmit

traffic of VLAN 2 in both directions, VLAN attribute registration must be performed

from Device C to Device A as follows:





After VLAN attribute registration is completed in the direction from Device A to

Device C, manually create VLAN 2 on Device C, changing its attribute from

dynamic to static. Upon the creation, Port 4 starts its Join timer and Hold timer

at the same time. When the Hold timer expires, Port 4 sends out the first JoinIn

message (a JoinIn message is sent because VLAN 2 has been registered on

Port 4) to Device B. When the Join timer expires, Port 4 restarts the Hold timer.

When the Hold timer expires, Port 4 sends out the second JoinIn message.

Upon receiving the first JoinIn message, Device B dynamically assigns the

receiving port Port 3 to VLAN 2, and instructs Port 2 to start its Join timer and

Hold timer at the same time. When the Hold timer expires, Port 2 sends out the

first JoinIn message to Device A. When the Join timer expires, Port 2 restarts

the Hold timer. When the Hold timer expires, Port 2 sends out the second JoinIn

message. Upon receiving the second JoinIn message, Device B does not

perform any processing, because Port 3 has been assigned to dynamic VLAN 2.

Upon receiving a JoinIn message, Device A stops sending JoinEmpty

messages to Device B. Thereafter, when the LeaveAll timer expires on a device

or a LeaveAll message is received on a device, the device re-starts the

LeaveAll timer, Join timers, Hold timers, and Leave timers on it. When the Hold

timer on Port 1 expires, Port 1 sends a JoinIn message.

Device B sends a JoinIn message to Device C.

Upon receiving the JoinIn message, Device C does not dynamically create

VLAN 2, because static VLAN 2 already exists on it.

3. Unidirectional VLAN attribute deregistration Device A

Device B

Device C

LeaveIn

LeaveEmpty

Static VLAN 2

Port 1

Port 2 Port 3

Port 4

Figure 7 Unidirectional VLAN attribute deregistration





If none of the devices in the network needs VLAN 2 any more, GVRP can help you

remove VLAN 2 from these devices through VLAN attribute deregistration as follows.

Remove static VLAN 2 from Device A. Upon the removal action, Port 1 starts itsHold timer. When the Hold timer expires, Port 1 sends a LeaveEmpty message

to Device B. Note that the LeaveEmpty message is sent only once.

Upon receiving the LeaveEmpty message, Port 2 on Device B starts its Leave

timer. When the Leave timer expires, Port 2 deregisters VLAN 2 on it to leave

VLAN 2. (In this case, as Port 3 is still in VLAN 2, Device B does not remove

VLAN 2.) At the same time, Port 2 instructs Port 3 to start its Hold timer and

Leave timer. When the Hold timer expires, Port 3 sends a LeaveIn message to

Device C. Because static VLAN 2 has not been removed from Device C yet,

Port 3 can still receive JoinIn messages from Port 4 before its Leave timer

expires. As a result, Device A and Device B can still learn dynamic VLAN 2.

Upon receiving the LeaveIn message, Device C does not remove Port 4 from

VLAN 2, because static VLAN 2 still exists on it.

4. Bidirectional VLAN attribute deregistration Device A

Device B

Device C

LeaveEmpty

LeaveEmpty

Port 1 Port 4

Port 3Port 2

Figure 8 Bidirectional VLAN attribute deregistration

To remove VLAN 2 from all devices in the network, you must trigger bidirectional

VLAN attribute deregistration in the reverse direction as follows:





Remove static VLAN 2 from Device C. Immediately, Port 4 starts its Hold timer.

When the Hold timer expires, Device C sends a LeaveEmpty message to

Device B.

Upon receiving the LeaveEmpty message, Port 3 on Device B starts its Leave

timer. When the Leave timer expires, Port 3 deregisters VLAN 2 on it, that is,

Port 3 exits VLAN 2, and dynamic VLAN 2 is removed as a result. At the same

time, Port 2 is instructed to start the Hold timer. When the Hold timer expires,

Port 2 sends a LeaveEmpty message to Device A.

Upon receiving the LeaveEmpty message, Port 1 on Device A starts its Leave

timer. When the Leave timer expires, Port 1 deregisters VLAN 2 on it, that is,

Port 1 exits dynamic VLAN 2, and dynamic VLAN 2 is removed as a result.

2.4 Restrictions GVRP is mutually exclusive with the service loopback feature. A service

loopback-enabled port cannot send out GVRP protocol packets.

GVRP can run only on common and internal spanning trees (CISTs) of MSTP.

Additionally, a CIST port blocked by MSTP cannot receive or transmit GVRP

protocol packets.

3 Application Scenarios GVRP maintains and updates VLAN information on different devices dynamically.

With GVRP, you just need to perform VLAN configuration on few devices and the

VLAN configuration will be applied to the whole switched network, thus saving the

time of topology analysis and configuration management.

As shown in Figure 9 , all devices are GVRP-enabled and connected with trunk ports

permitting traffic of all VLANs to pass through. Manually configure static VLANs 100

through 1000 on Device A and Device G. Then, Device B through Device F can learn

these VLANs with GVRP. At last, VLAN 100 through VLAN 1000 are created on each

device in the network.





Device A Device B

Device C

Device D

Device E

VLAN 100 - 1000

Device F Device G

VLAN 100 - 1000

Figure 9 Application scenarios

4 Prospect As a dynamic VLAN configuration technology, GVRP simplifies VLAN configuration

management in a complicated network and reduce network intercommunication

problems caused by inconsistent configurations. Additionally, because GVRP does

not assign a port receiving no VLAN registration message to dynamic VLANs, you

can configure GVRP appropriately to control the size of a VLAN, suppressing

unnecessary traffic. As GVRP has supported multiple MSTIs in MSTP, it is believed

that GVRP can gain wider application.

5 References IEEE Std 802.1D

IEEE Std 802.1Q

Copyright ©2008 Hangzhou H3C Technologies Co., Ltd. All rights reserved. No part of this manual may be reproduced or transmitted in any form or by any means without prior written consent of

Hangzhou H3C Technologies Co., Ltd. The information in this document is subject to change without notice.

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