[rbridge] VLAN mapping anonmolies...does anyone care?
Anil_R at 3com.com
Mon Dec 14 06:28:17 PST 2009
I'd say it would be best to define it in such a way that, once a switch has
been given a VLAN mapping from one port to another, it either rejects a
different mapping or overrides the old one, depending on how the MIB is
defined. Which is to say, make it "invertible" always.
In practice, this sort of connectivity when desired by customers is done in
a way that doesn't require VLAN mapping: you'd define "overlapping VLANs"
which allow, in this example, VLAN A as well as VLAN B to reach the ports
of VLAN C, but do not allow VLAN A and VLAN B to talk to each other (if
that were the requirement.)
In another scenario, you may have 3 different sites East, West and South,
where West wants its VLAN A to be translated to VLAN C in the East and
South wants its VLAN B to be translated to the same VLAN C in the East
(vice versa for the opposite direction). In such a case you would have 3
switches (connecting East, West and South), each of which have invertible
mappings. This is a much more common application of VLAN mapping: site
administrators define their own VLANs, then their edge switches translate
when necessary to connect into VLANs in a different site.
rbridge-bounces at postel.org wrote on 12/12/2009 06:12:31 PM:
> Radia Perlman <Radia.Perlman at Sun.COM>
> Sent by: rbridge-bounces at postel.org
> 12/12/2009 06:12 PM
> rbridge at postel.org
> [rbridge] VLAN mapping anonmolies...does anyone care?
> A couple of things to bring to people's attention in fewer words than
> reading the VLAN mapping draft. :-)
> a) if mappings are not invertible, as in, both VLAN A and VLAN B in East
> map to VLAN C in West,
> then it's not clear what to map VLAN C to, when forwarding from West to
> I'd say either make that a configuration error and don't let someone
> configure two VLANs that map
> to the same thing, or say that when mapping from (West, VLAN C), if both
> A and B from East map to (West, C),
> then map to the highest VLAN number, or the first one listed in the
> mapping configuration table. Other
> b) if mappings are not invertible, same example as a). and the path goes
> from East to West and then East
> again, VLAN A in East might wind up getting mapped to VLAN B in East.
> I don't care -- I think noninvertible mappings should be illegal.
> c) another form of noninvertible mapping is (East, VLAN A : West, null),
> meaning that VLAN A in East
> should be dropped instead of being forwarded to cloud West. The
> surprising result of this, if the path
> goes from East to West and back to East, is that VLAN A might become
> partitioned as a result.
> I don't care, especially since I can't think of any good, simple
> solution to this.
> rbridge mailing list
> rbridge at postel.org
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