Subject: [rbridge] Readiness of the VLAN Mapping Draft

From: Donald Eastlake <[email-masked]>
Date: Mon, 29 Mar 2010 15:08:33 -0400

At the Anaheim meeting I suggested that it might be time for a Working Group
Last Call on the VLAN Mapping Draft:
http://tools.ietf.org/html/draft-ietf-trill-rbridge-vlan-mapping-02

However, in reviewing that document, I noticed an inconsistency:

The draft assumes that you configure rules of the form [ v1, r1 -> v2, r2 ],
which means that if you receive a frame in VLAN 1 from a port connected to
Region 1 and you output that frame to a port connected to Region 2, you map
the VLAN of the from to VLAN 2.

At one place in the draft there is a paragraph beginning "Note that mappings
are always symmetric" which says that if you have configured a rule [ v1, r1
-> v2, r2 ] then the RBridge will also act as if you had a rule [ v2, r2 ->
v1, r1 ] in place. However, in the more explicit description of the rules
for mapping, just below that paragraph, it implies that translations are
only caused by explicit rules where the "from" VLAN and region and the "to"
region match. (Either way there is an implication that you can't have
directly conflicting rules, that is two rules that differ only in the "to"
VLAN.)

There are two way to clarify this possible inconsistency:

(A) Stick with the explicit rule description, which means that having a [
v1, r1 -> v2, r2 ] in place would have no effect on a frame in VLAN 2
received from Region 2 and being forwarded into Region 1.  If there were no
other matching explicit rule, such a frame would not be mapped.

(B) Stick with the description where translations can occur due to an
explicit rules or implicitly for the inverse of the rule. Thus an explicit [
v1, r1 -> v2, r2 ] would also imply [ v2, r2 -> v1, r1 ] unless there was an
different explicit rules for VLAN 2 frames from Region 2 being forwarded to
Region 1. This would generally mean fewer rules to configure but also the
possibility of conflicting implied rules. For example, you could have both [
v1, r1 -> v2, r2] and [ v3, r1 -> v2, r2 ] in which case what to do with a
frame in VLAN 2 from Region 2 being forwarded to Region 1 is unclear and the
draft would either have to specify a tie-breaker or say the result is
unspecified.

Would people prefer A or B?

Thanks,
Donald
=============================
Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
155 Beaver Street
Milford, MA 01757 USA
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From: Radia Perlman <[email-masked]>
Date: Mon, 29 Mar 2010 12:41:04 -0700

I think I'd prefer if rules were symmetric, as in

(East, VLAN A) = (West, VLAN B)
or
(East, VLAN C) = (West, null)

And if there is already a rule for
(East, VLAN A) = West, VLAN B)
and you try to configure
(East, VLAN D) = (West, VLAN B)
that you get an warning, saying "(West, VLAN B) is already mapped to
(East, VLAN A). Do you wish to supercede that rule?"

However, as someone that is always annoyed when a newer version of
something changes the user interface after I've finally gotten used to
the older version, even if the engineers think the new commands are
better somehow, it means I have to figure out how it works again....

The questions is....bridges do VLAN mapping. How are bridges
configured with VLAN mapping? Are mappings one-way? Are they allowed
to be configured to not be one-to-one?

Radia

On Mon, Mar 29, 2010 at 12:08 PM, Donald Eastlake <[email-masked]> wrote:
> Last Call on the VLAN Mapping
> Draft: http://tools.ietf.org/html/draft-ietf-trill-rbridge-vlan-mapping-02

---

From: Joe Touch <[email-masked]>
Date: Mon, 29 Mar 2010 16:23:14 -0700

> (East, VLAN C) = (West, null)

FWIW, if they're not symmetric, isn't there potential for some sort of loop?

Joe

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From: Radia Perlman <[email-masked]>
Date: Mon, 29 Mar 2010 16:50:15 -0700

There's no possibility of a loop. VLAN mapping is completely
independent of the path that a packet takes, and since TRILL stands on
its head to ensure no loops of either unicast or multicast, any
particular packet will only go some number of hops. During that time,
the VLAN might get mapped multiple times and in strange ways, but VLAN
mapping won't cause the packet to take a different path.

In other words, for unicast, the VLAN marking is independent of the
path it takes. For multidestination frames, the only way the VLAN
influences the path is whether the packet gets filtered instead of
being forwarded on all branches of the selected tree.

Radia

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From: Donald Eastlake <[email-masked]>
Date: Tue, 30 Mar 2010 00:46:00 -0400

> (East, VLAN C) = (West, null)

I don't think the second rule above is symmetric because you can't have a
frame sourced with the null VLAN.

> (East, VLAN A). Do you wish to supercede that rule?"

I care more about the protocol machinery and bits on the wire than the user
interface.

Sounds like you want a symmetric reversible mapping except that VLANs can be
mapped to null which means to drop the frame... (The current sub-TLV for
optionally reporting VLAN mapping is specified on page 31 of
draft-ietf-isis-layer2-03.txt.)

I think one way to put what you want is that adding a new rule [ rA, vA =
rB, vB ] conflicts with and causes an existing rule [ rC, vC = rD, vD ] to
be deleted if:

rA == rC && vA == vC && vA != null && rB == rD && vB != vD
OR
rB == rD && vB == vD && vB != null && rA == rC && vA != vC

(also a rule cannot specify the null VLAN on both sides of the equal sign)

Donald

> > Draft: