Subject: [rbridge] Proposed replacement for a paragraph in section 2.3 of draft-ietf-trill-rbridge-protocol-07

From: Claudio DeSanti <[email-masked]>
Date: Mon, 10 Mar 2008 07:18:51 -0700

Hi all,

as just presented, this is a proposed clarification for an existing 
paragraph in section 2.3 of the base protocol spec.
Thanks,

              Claudio.

-------

Existing paragraph:

   By default, RBridges tag IS-IS Hellos with VLAN 1. However, an
   RBridge MAY be configured to transmit Hellos on a set of VLANs, and
   if elected DRB, to designate to the other RBridges on the link which
   VLAN to tag Hellos with. Once the DRB, say RB1, is elected, and
   specifies the designated VLAN, say VLAN-x, on which to send Hellos,
   (1) all RBridges on the link, except the DRB, transmit Hellos tagged
   only with VLAN-x, (2) all RBridge-RBridge communication (including
   Hellos, forwarded data packets, and LSPs) are tagged with VLAN-x, and
   (3) the DRB only lists, in its Hello, and in the pseudonode LSP, the
   set of RBridges from which the DRB hears VLAN-V tagged packets.

Proposed replacement:

An RBridge maintains per each port the following parameters:
a) Announcing VLANs set: the set of VLANs where an RBridge port 
announces IS-IS Hellos on a link;
b) Designated VLAN: the VLAN used by an RBridge port to communicate with 
other RBridge ports on a link; and
c) Forwarding VLANs set: the set of VLANs for which an RBridge port is 
appointed VLAN forwarder on a link.

By default the Announcing VLANs set contains all the VLANs active on the 
port, however it may be configured to contain a subset of them.

When a port of an RBridge becomes operational, the RBridge MUST transmit 
IS-IS Hellos on each VLAN of the Announcing VLANs set of that port.

If the RBridge is elected DRB for the link to which that port is 
connected, the RBridge MUST:
a) continue to send IS-IS Hellos per each VLAN of the Announcing VLANs 
set of that port;
b) designate the Designated VLAN to be used to communicate with the 
other RBridges connected to that link; and
c) establish the Forwarding VLANs set per each RBridge connected to that 
link, including itself.

If the RBridge is not elected DRB for the link to which that port is 
connected and its Forwarding VLANs set is not empty, the RBridge MUST:
a) learn from the DRB the Designated VLAN on that link;
b) act as a VLAN forwarder for the VLANs included in its Forwarding 
VLANs set; and
c) transmit IS-IS Hellos messages only on the Designated VLAN and on the 
VLANs of its Forwarding VLANs set.

If the RBridge is not elected DRB for the link to which that port is 
connected and its Forwarding VLANS set is empty, the RBridge MUST:
a) learn from the DRB the Designated VLAN on that link; and
b) transmit IS-IS Hellos messages only on the Designated VLAN.
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---

From: Radia Perlman <[email-masked]>
Date: Wed, 19 Mar 2008 07:19:10 -0700

Not sure what's wrong with the paragraph to be replaced, other than
a) the last line says "VLAN-V" when it shbould be "VLAN-x", and
b) it doesn't mention which VLANs to act as appointed forwarder on, 
though I think that is
elsewhere in the spec.

It would be easier to evaluate the replacement text if you explained 
what is being fixed. Is it
a technical change? (I think not, but maybe there's something subtle 
there that you are trying
to fix). Or is it only editorial, to make things more precise? Or is it 
to include the
explanation of appointed VLAN forwarders? (which  is already explained 
elsewhere in
the base spec, I think, for instance, section 4.2.4,   4.2.5). But I 
could not find a section
that talks about what is in IS-IS Hellos, where presumably we'd explain 
about the set of
VLANs to volunteer to be VLAN forwarder for, and where the DRB appoints 
VLAN forwarders
in its own Hello.

As for the proposed replacement
text...it is mostly fine, though it's harder to read I think, and 
certainly longer. Maybe it's
more precise, but for instance:
"

c) Forwarding VLANs set: the set of VLANs for which an RBridge port is 
appointed VLAN forwarder on a link."

implies that an RBridge forwards on that set regardless of what the DRB says.
In fact, the DRB has to be the one to appoint the forwarder. Perhaps this
should be called "Potential forwarding VLAN set" and later, in

"
VLANs set; and"

say "act as a VLAN forwarder for the VLANs which the DRB appoints it to be
forwarder for"

And also, a non-DRB must list, in its HEllo, the "potential forwarding set",
and the DRB must specify somehow (logically in the IS-IS Hello, but in theory
the DRB's Hello could get too large if the DRB has to appoint VLAN forwarders
on a fairly random set of VLANs).

We could say the DRB R1 can specify a range of VLANs for
R2 to be appointed forwarder on, and it only means the set of
VLANs in the range that R2 volunteered for when R2 announced, in its own Hello,
its potential forwarding set.

Radia

---

From: "Silvano Gai" <[email-masked]>
Date: Wed, 19 Mar 2008 08:30:45 -0700

Radia,

There are many differences:
1) the old text is not "per port"
2) the "default case" of the old text is not what we have discussed
3) The old text does not specify the forwarder sending hello on the
forwarded VLANs

-- Silvano

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]
On
> Behalf Of Radia Perlman
> Sent: Wednesday, March 19, 2008 7:19 AM
> To: Claudio DeSanti
> Cc: [email-masked]
> Subject: Re: [rbridge] Proposed replacement for a paragraph in section
> 2.3of draft-ietf-trill-rbridge-protocol-07
> 
> implies that an RBridge forwards on that set regardless of what the
DRB
> says.
> VLANs in the range that R2 volunteered for when R2 announced, in its
own
> Hello,