Subject: [rbridge] Core Rbridge instance PDU packet encapsulation

From: sanjays at cisco.com (Sanjay Sane (sanjays))
Date: Tue, 11 Jul 2006 18:22:11 -0700

Hi,
 
It seems PDUs of core Rbridge instance are supposed to go without VLAN
Tag, i.e. no .1Q tag. typically, when a classical bridge gets an
untagged packet (either on an access port or trunk port), it treats the
packet as if its coming on the default port-vlan. It will forward the
packet only within that vlan. 
 
Consider the the case where 2 Rbridges are connected through a classical
bridge. Lets say the 2 ports of this classical bridge, on which the 2
Rbridges are connected, are configured as trunk ports. Both these ports
also have a default port-vlan. 
Now, untagged packets coming from one Rbridge will reach the other
Rbridge *only* if the default port-vlans are the same. 
 
If the 2 Rbridges were connected through a network of classical bridges
(instead of a single classical bridge), are we relying on the assumption
that default port-vlans are the same. Why not use a VLAN tag (.1Q) for
the PDU packets of the core Rbridge instance as well ? 
 
Thanks.
Sanjay
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From: saikat at seas.upenn.edu (Saikat Ray)
Date: Tue, 11 Jul 2006 21:35:33 -0400

This was discussed before and, if I remember right, the conclusion was that
it is a VLAN configuration issue: i.e., it is assumed that VLANs are
configured correctly on all bridges so that there is no weird/unexpected
behavior.

The issue you pointed out actually holds for any encapsulated packet: what
VLAN ID should the outer headers use ...

________________________________________
From: rbridge-bounces at postel.org [mailto:rbridge-bounces at postel.org] On
Behalf Of Sanjay Sane (sanjays)
Sent: Tuesday, July 11, 2006 9:22 PM
To: rbridge at postel.org
Subject: [rbridge] Core Rbridge instance PDU packet encapsulation

Hi,
?
It seems PDUs of core Rbridge instance are supposed to go without VLAN Tag,
i.e. no .1Q tag. typically, when a classical bridge gets an untagged packet
(either on an access port or trunk port), it treats the packet as if its
coming on the default port-vlan. It will forward the packet only within that
vlan. 
?
Consider the the case where 2 Rbridges are connected through a classical
bridge. Lets say the 2 ports of this classical bridge, on which the 2
Rbridges are connected, are configured as trunk ports. Both these ports also
have a default port-vlan. 
Now,?untagged packets coming from one Rbridge will reach the other Rbridge
*only* if the default port-vlans are the same. 
?
If the 2 Rbridges were connected through a network of classical bridges
(instead of a single classical bridge), are we relying on the assumption
that default port-vlans are the same. Why not use a VLAN tag (.1Q) for the
PDU packets of the core Rbridge instance as well ? 
?
Thanks.
Sanjay