GVRP protocol.(vlan GARP protocol)

GVRP protocol.(vlan GARP protocol)

Post by prasad5.. » Wed, 14 Jul 1999 04:00:00



Hi all,
I have some doubts regarding GARP(Generic attribute registration
protocol)VLAN Registration protocol(GVRP).In this protocol, as per the
IEEE draft, GVRP PDU is sent to get the GVRP registration. How is it
accomplished? Is it in the similar way as that of the BPDU( Spanning
tree) packets sent between the Bridges?
Thank you!
Regards,
Prasad.

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GVRP protocol.(vlan GARP protocol)

Post by Rich Seife » Wed, 14 Jul 1999 04:00:00



> I have some doubts regarding GARP(Generic attribute registration
> protocol)VLAN Registration protocol(GVRP).In this protocol, as per the
> IEEE draft, GVRP PDU is sent to get the GVRP registration. How is it
> accomplished? Is it in the similar way as that of the BPDU( Spanning
> tree) packets sent between the Bridges?

I'm not sure what you mean "in a similar was as that of BPDU". GVRP
messages are sent among VLAN-aware devices to register their "membership"
in a given VLAN on a given port (or to de-register it). What "doubts" do
you have regarding the protocol?

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(408) 395-5700                  Los Gatos, CA 95033
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GVRP protocol.(vlan GARP protocol)

Post by prasad5.. » Thu, 15 Jul 1999 04:00:00


 I have some doubts regarding GARP(Generic attribute registration
 protocol)VLAN Registration protocol(GVRP).In this protocol, as per
the
 IEEE draft, GVRP PDU is sent to get the GVRP registration. How is it
 accomplished? Is it in the similar way as that of the BPDU( Spanning
 tree) packets sent between the Bridges?
----------------------------------------------
 I'm not sure what you mean "in a similar was as that of BPDU". GVRP
 messages are sent among VLAN-aware devices to register their
"membership"
 in a given VLAN on a given port (or to de-register it). What "doubts"
do
 you have regarding the protocol?
-------------------------------------------
Ya you have answered my question:- "GVRP
 messages are sent among VLAN-aware devices to register their
"membership". Can you please elaborate this senence. I mean is there a
typical packet sent amoung the VLAN-aware devices. If yes then contents
of the packet might be :
Destination address : 01-80-C2-00-00-21,
Source address      : Address of the sender,
TAG field           : 4-byte.
type/length
data
Fcs etc
 what are the contents of type/length and Data fields?
Thank you,
Reagards,
Prasad Chavan.

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GVRP protocol.(vlan GARP protocol)

Post by Rich Seife » Thu, 15 Jul 1999 04:00:00



> Ya you have answered my question:- "GVRP
>  messages are sent among VLAN-aware devices to register their
> "membership". Can you please elaborate this senence. I mean is there a
> typical packet sent amoung the VLAN-aware devices. If yes then contents
> of the packet might be :
> Destination address : 01-80-C2-00-00-21,
> Source address      : Address of the sender,
> TAG field           : 4-byte.
> type/length
> data
> Fcs etc
>  what are the contents of type/length and Data fields?

First of all, GVRP messages are never sent "tagged", as you indicate. (This
would be a circular-logic problem--receiving a tagged frame requires
membership in the VLAN identified by the tag, but you need GVRP to register
the membership!)

GVRP messages use Length encapsulation (not Type). After the Length is the
LLC-1 header, using DSAP=SSAP=0x42, and UI=0x03, the same as the Spanning
Tree Protocol. Following the LLC header, the BPDU protocol identifier is
0x01, to identify it as a GARP message, rather than 0x00 as used for
Spanning Tree.

The attached pdf file is a page from my upcoming book that contains the
GVRP message format.

--
Rich Seifert                    Networks and Communications Consulting

(408) 395-5700                  Los Gatos, CA 95033
(408) 395-1966 FAX
"... specialists in Local Area Networks and Data Communications systems"

 
 
 

GVRP protocol.(vlan GARP protocol)

Post by prasad5.. » Fri, 16 Jul 1999 04:00:00


 First of all, GVRP messages are never sent "tagged", as you indicate.
(This
 would be a circular-logic problem--receiving a tagged frame requires
 membership in the VLAN identified by the tag, but you need GVRP to
register
 the membership!)

 GVRP messages use Length encapsulation (not Type). After the Length is
the
 LLC-1 header, using DSAP=SSAP=0x42, and UI=0x03, the same as the
Spanning
 Tree Protocol. Following the LLC header, the BPDU protocol identifier
is
 0x01, to identify it as a GARP message, rather than 0x00 as used for
 Spanning Tree.

 The attached pdf file is a page from my upcoming book that contains
the
 GVRP message format.
 --------
Now I am clear about the contents of the GVRP PDU.
Earlier you have mentioned that GVRP pdu should be sent by all VLAN
aware devices. Should  VLAN aware bridge send this GVRP PDU? if yes then
in VLAN ID field which VLAN ID it should transmit, because it can
support more than one VLAN?

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GVRP protocol.(vlan GARP protocol)

Post by Rich Seife » Fri, 16 Jul 1999 04:00:00



> Now I am clear about the contents of the GVRP PDU.
> Earlier you have mentioned that GVRP pdu should be sent by all VLAN
> aware devices. Should  VLAN aware bridge send this GVRP PDU? if yes then
> in VLAN ID field which VLAN ID it should transmit, because it can
> support more than one VLAN?

A VLAN-aware bridge is clearly a VLAN-aware device, so yes, it sends GVRP
messages. (I used the term "device" rather than "station", to indicate both
stations and bridges.) A bridge will register as many VLAN IDs as it needs
to, based on the VLAN configuration. If you note from the frame format,
more than one VLAN ID can be registered/de-registered in a single GVRP
message.

--
Rich Seifert                    Networks and Communications Consulting

(408) 395-5700                  Los Gatos, CA 95033
(408) 395-1966 FAX
"... specialists in Local Area Networks and Data Communications systems"

 
 
 

GVRP protocol.(vlan GARP protocol)

Post by pra.. » Sat, 17 Jul 1999 04:00:00


 A VLAN-aware bridge is clearly a VLAN-aware device, so yes, it sends
GVRP
 messages. (I used the term "device" rather than "station", to indicate
both
 stations and bridges.) A bridge will register as many VLAN IDs as it
needs
 to, based on the VLAN configuration. If you note from the frame
format,
 more than one VLAN ID can be registered/de-registered in a single GVRP
 message.

------------------------------------------------------------------------
 I got it. One more doubt:
What are the different reasons for untagging the frame?
One is when the packet is received from VLAN aware device and is to be
transmitted to the VLAN unaware device. Is there other conditions that
should be considered while stripping the tag?

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GVRP protocol.(vlan GARP protocol)

Post by Rich Seife » Sat, 17 Jul 1999 04:00:00



> What are the different reasons for untagging the frame?
> One is when the packet is received from VLAN aware device and is to be
> transmitted to the VLAN unaware device. Is there other conditions that
> should be considered while stripping the tag?

Frames can only be sent tagged when ALL devices that may need to hear it
are tag-aware. For example, a multicast being sent to a mix of tag-aware
and tag-unaware devices on a shared LAN segment must be sent untagged, or
the tag-unaware devices won't understand it.

Also note that a device can be VLAN-aware without being tag-aware. Take the
example of a simple switch with port-based VLAN capabilities. It can
isolate traffic among VLANs by virtue of the fact that it will not forward
frames between ports that are not part of the same VLAN. However, it may
not understand tags at all. VLAN-awareness and tag-awareness are two
different things (although if you are tag-aware, you are clearly
VLAN-aware; the reverse is not true).

--
Rich Seifert                    Networks and Communications Consulting

(408) 395-5700                  Los Gatos, CA 95033
(408) 395-1966 FAX
"... specialists in Local Area Networks and Data Communications systems"

 
 
 

GVRP protocol.(vlan GARP protocol)

Post by pra.. » Tue, 20 Jul 1999 04:00:00


 Frames can only be sent tagged when ALL devices that may need to hear
it are tag-aware. For example, a multicast being sent to a mix of tag-
aware and tag-unaware devices on a shared LAN segment must be sent
untagged, or the tag-unaware devices won't understand it.

 Also note that a device can be VLAN-aware without being tag-aware.
Take the example of a simple switch with port-based VLAN capabilities.
It can isolate traffic among VLANs by virtue of the fact that it will
not forward frames between ports that are not part of the same VLAN.
However, it may not understand tags at all. VLAN-awareness and tag-
awareness are two different things (although if you are tag-aware, you
are clearly VLAN-aware; the reverse is not true).
------------------------------------------------------------------
Got it. Now one more doubt:
The frame format for the 802.3 SNAP packet contents are  as
shown bellow
--------------------------------------------------------------------
|| DA | SA | LN | DSAP |SSAP | Control | SNAP header | DATA | CRC ||
--------------------------------------------------------------------
||6-B |6-B |2-B | AA   | AA  | 03      | 5-B         |      | 4-B ||
--------------------------------------------------------------------
If this is to be the VLAN 802.3 SNAP packet what will be the packet
contents? Are the packet contents are like shown bellow:
--------------------------------------------------------------------/
|| DA | SA | LN | DSAP |SSAP | Control | orgnization |Tag-Type|TCI|
--------------------------------------------------------------------/
||6-B |6-B |2-B | AA   | AA  | 03      | 00-00-00    |81-00   |2-B|
--------------------------------------------------------------------/
-------------------------------------
| Ether-TYPE| E-RIF    | DATA |CRC ||
-------------------------------------
| 2-B       |2 to 30-B |      | 4-B||
-------------------------------------
(RIF field comes in to picture when the CFI bit in the TCI field is
set. )

Regards,
Prasad.

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GVRP protocol.(vlan GARP protocol)

Post by Rich Seife » Tue, 20 Jul 1999 04:00:00



> The frame format for the 802.3 SNAP packet contents are  as
> shown bellow
> --------------------------------------------------------------------
> || DA | SA | LN | DSAP |SSAP | Control | SNAP header | DATA | CRC ||
> --------------------------------------------------------------------
> ||6-B |6-B |2-B | AA   | AA  | 03      | 5-B         |      | 4-B ||
> --------------------------------------------------------------------
> If this is to be the VLAN 802.3 SNAP packet what will be the packet
> contents? Are the packet contents are like shown bellow:
> --------------------------------------------------------------------/
> || DA | SA | LN | DSAP |SSAP | Control | orgnization |Tag-Type|TCI|
> --------------------------------------------------------------------/
> ||6-B |6-B |2-B | AA   | AA  | 03      | 00-00-00    |81-00   |2-B|
> --------------------------------------------------------------------/
> -------------------------------------
> | Ether-TYPE| E-RIF    | DATA |CRC ||
> -------------------------------------
> | 2-B       |2 to 30-B |      | 4-B||
> -------------------------------------
> (RIF field comes in to picture when the CFI bit in the TCI field is
> set. )

No, it's the other way around. VLAN-tagged frames on an Ethernet ALWAYS
take a Type field encapsulation rather than Length. That is, the SNAP
header gets encapsulated into the Type-encapsulated VLAN frame format. The
frame would look like:

Quote:> --------------------------------------------------------------------/
> || DA | SA |Tag-Type| TCI | E-RIF | len |DSAP|SSAP| Control | OUI      |
> --------------------------------------------------------------------/
> ||6-B |6-B |  8100  | 2-B | 2-30B | 2B  |AA  |AA  | 03      | xx-yy-zz |
> --------------------------------------------------------------------/
> -------------------------------------
> | Ether-TYPE| DATA |CRC ||
> -------------------------------------
> | 2-B       |      | 4-B||
> -------------------------------------
> (RIF field comes in to picture when the CFI bit in the TCI field is
> set. )

--
Rich Seifert                    Networks and Communications Consulting

(408) 395-5700                  Los Gatos, CA 95033
(408) 395-1966 FAX
"... specialists in Local Area Networks and Data Communications systems"
 
 
 

GVRP protocol.(vlan GARP protocol)

Post by pra.. » Wed, 21 Jul 1999 04:00:00


 No, it's the other way around. VLAN-tagged frames on an Ethernet
ALWAYS
 take a Type field encapsulation rather than Length. That is, the SNAP
 header gets encapsulated into the Type-encapsulated VLAN frame format.
The
 frame would look like:

--------------------------------------------------------------------/
|| DA | SA |Tag-Type| TCI | E-RIF | len |DSAP|SSAP| Control | OUI
--------------------------------------------------------------------/
||6-B |6-B |  8100  | 2-B | 2-30B | 2B  |AA  |AA  | 03      |xx-yy-zz |
--------------------------------------------------------------------/
-------------------------------------
| Ether-TYPE| DATA |CRC ||
-------------------------------------
| 2-B       |      | 4-B||
-------------------------------------
For tag-type field, now clear, but as per the draft the E-RIF field
comes after the length field. Here you have mentioned before the Leangth
field. Is that is correct?

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GVRP protocol.(vlan GARP protocol)

Post by Rich Seife » Wed, 21 Jul 1999 04:00:00



>  No, it's the other way around. VLAN-tagged frames on an Ethernet
> ALWAYS
>  take a Type field encapsulation rather than Length. That is, the SNAP
>  header gets encapsulated into the Type-encapsulated VLAN frame format.
> The
>  frame would look like:

> --------------------------------------------------------------------/
> || DA | SA |Tag-Type| TCI | E-RIF | len |DSAP|SSAP| Control | OUI
> --------------------------------------------------------------------/
> ||6-B |6-B |  8100  | 2-B | 2-30B | 2B  |AA  |AA  | 03      |xx-yy-zz |
> --------------------------------------------------------------------/
> -------------------------------------
> | Ether-TYPE| DATA |CRC ||
> -------------------------------------
> | 2-B       |      | 4-B||
> -------------------------------------
> For tag-type field, now clear, but as per the draft the E-RIF field
> comes after the length field. Here you have mentioned before the Leangth
> field. Is that is correct?

Sorry, my error. The E-RIF does come after the original length/type field.
That is, the original length/type field is always offset by exactly 4
bytes. In practice, you will rarely (if ever) see an E-RIF field on an
Ethernet frame.

--
Rich Seifert                    Networks and Communications Consulting

(408) 395-5700                  Los Gatos, CA 95033
(408) 395-1966 FAX
"... specialists in Local Area Networks and Data Communications systems"

 
 
 

GVRP protocol.(vlan GARP protocol)

Post by pra.. » Fri, 23 Jul 1999 04:00:00


One more doubt: -
Whether the Bridge has to forward the GVRP-PDU to other Bridges?

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GVRP protocol.(vlan GARP protocol)

Post by Rich Seife » Fri, 23 Jul 1999 04:00:00



> Whether the Bridge has to forward the GVRP-PDU to other Bridges?

If a bridge is implementing GVRP, then it sinks all GVRP messages and
doesn't forward them to other bridges. If a bridge does NOT implement GVRP
(i.e., it is VLAN-unaware), then it does forward the GVRP messages as
normal multicasts. This should all be clear in the 802.1Q standard.

--
Rich Seifert                    Networks and Communications Consulting

(408) 395-5700                  Los Gatos, CA 95033
(408) 395-1966 FAX
"... specialists in Local Area Networks and Data Communications systems"