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VLAN-Aware switch query...

Last response: in Networking
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Anonymous
June 6, 2005 11:28:02 AM

Archived from groups: comp.dcom.lans.ethernet (More info?)

Hi All,

I have Following ambiguity regarding VLAN functionality, your answer
will be really great helpful to me.

Actually, I am working on the ethernet switch which supports Packet
classification engine.

Packet classification engine support VLAN-id assignment via
-programming specific pattern in the rule table.

I mean to say packet classification engine parses L2 header and L3
header, if parser out put matches with program pattern, it assign
specific vlan-id (vlan-id is also programmable).

I have observed that packet classification engine assign new VLAN-ID to
incoming frame (if parser output matches with program pattern) even
though it is already VLAN-TAG frame.

As per standard 802.1Q ,I understood that packet classification must
not assign new VLAN-ID based on packet classification engine if
incoming frame is already vlan-tagged frame, I am right ? or not.

Please add your point, it would be really great support to me.

Thanks in advance
Dilip
Anonymous
June 6, 2005 6:21:31 PM

Archived from groups: comp.dcom.lans.ethernet (More info?)

dilip_1379@hotmail.com wrote:

> I mean to say packet classification engine parses L2 header and L3
> header, if parser out put matches with program pattern, it assign
> specific vlan-id (vlan-id is also programmable).

IEEE 802.1Q only supports VLAN assignment based on port and protocol,
so this level of classification is clearly beyond the scope of the
standard.

> I have observed that packet classification engine assign new VLAN-ID to
> incoming frame (if parser output matches with program pattern) even
> though it is already VLAN-TAG frame.
>
> As per standard 802.1Q ,I understood that packet classification must
> not assign new VLAN-ID based on packet classification engine if
> incoming frame is already vlan-tagged frame, I am right ? or not.

Per the standard, the bridge should always use the tag in the frame
if one is already there. You can control which frames you receive
from the port using "Admit Only VLAN-tagged Frames" or
"Admit Only Untagged and Priority-tagged Frames" setting for the
port.

Maybe the switch that you are working with is simply treating all
frames it receives on that port as untagged. Does it replace the
existing tag, or does it put a second tag in the frame, when forwarding

a frame that came in tagged out a port that is in the VLAN's tagged
set?

Anoop
!