Subject: [rbridge] Queries on vlan-mapping

From: somnath chatterjee <[email-masked]>
Date: Wed, 7 Dec 2011 23:52:19 +0530

Hi Authors,

According to base TRILL RFC 6325 whenever a Designated RBridge(DRB) on
a link detects that
there is vlan mapping on the link, (by recieving Hellos with with vlan
mapping flag set or by inspecting
 outer vlan mismatch with vlan tag in Hello) it revokes all
appointment of vlan-x forwarders and itself
becomes appointed forwarder for all vlans.

Assuming the following scenario where four RBridges are connected to
the same link which
has a Vlan Mapping device and there are other end stations connected
to this link. Say RB1
is the DRB for the link. We assume there are two regions one being the
DRB side of link and
other being the Non DRB side of link. Why can't DRB appoint vlan-x
forwarders to RBridge(s) connected
on the DRB side of the link? ie why can't RB1 appoint RB3 as appointed
forwarder for some vlans?

    DRB side of link                                       Non DRB side of link

+-----------+           +-------------------------------+          +-----------+
+ RB1    + - - - - - + Vlan Mapping device+ - - - - -+  RB2   +
+-----------+   |       +-------------------------------+    |
+-----------+
                  |                                              |
           +-----------+                               +------------+
           +  RB3   +                               +  RB4   +
           +-----------+                               +------------+

For DRB to identify whether a RB is on DRBs side of link or on the non-DRB side

1> If DRB recieves a Hello from RB with Outer vlan matching the vlan
tag in Hello and
the vlan mapping flag is set in the Hello, the DRB can assume the RB
is on DRB side of the link.

2> If DRB recieves a Hello from RB with Outer vlan different from the
vlan tag in Hello and
the vlan mapping flag is set in the Hello, the DRB can assume the RB
is on non-DRB side of the link.

Here if RB1(DRB) appoints RB3 as vlan x forwarder for vlan on which
the RB1(DRB) has recieved a Hello
with vlan mapping flag enabled and Outer vlan being same as the vlan
tag in Hello, will there be any problem?

Thank you,
Regards,
Somnath

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