Subject: [rbridge] Queries on RFC 6325

From: rakesh kumar <[email-masked]>
Date: Mon, 5 Dec 2011 15:01:41 +0530

Hi All,

     Can any one clarify what exactly is the role of access port.To
be very specific should the access port act as appointed forwarder for
end-station enabled vlans.

1. According following lines mentioned in RFC section 4.9.1,its clear
that Access port should not become appointed forwarder for any vlans:

    "If the DRB RB1 does not have this bit set, but neighbor RB2 on
the link does have the bit set, then RB1 does not appoint RB2
asappointed forwarder for any VLAN, and none of the RBridges
(including the pseudonode) report RB2 as a neighbor in LSPs."

But the problem is RBridge access port would be expected to lead to a
link with end stations,as access port leads to end-station it is
suppose to act as Appointed forwarder to convert native to TRILL and
TRILL to native form.

2.And according to lines mentioned in RFC section 4.9.1,i am not clear
whether RB1 appoints himself as appointed forwarder for any vlans?

"If RB1 is the DRB and has this bit set(access) in its TRILL-Hello,
the DRB still appoints VLAN forwarders."

Regards,
Rakesh

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From: Donald Eastlake <[email-masked]>
Date: Mon, 5 Dec 2011 22:37:13 -0500

Hi Rakesh,

> end-station enabled vlans.

I don't know what you mean by "end-station enabled vlans" or what
would be special about them. But the idea is that if a link is an
access link, then all the RBridge ports on the link would normally be
configured as access ports and thus have the access bit on in the
Hellos that they send. TRILL Hellos would still be exchanged over the
link but adjacencies would not be reported (unless you are using the
pseudo node with overflow set option). Thus through TRILL Data would
not be sent over the link. On such a properly configured link,
Appointed Forwarders set up is as normal.

> suppose to act as Appointed forwarder to convert native to TRILL and

If the DRB port on the link is not an access port but some other
RBridge's port is an access port, the link is misconfigured. It would
probably work fine to appoint an RBridge with an access port on such a
misconfigured link as an Appointed Forwarder. But, since that RBridge
disagrees with the DRB about the type of service being provided on the
link and the DRB is, generally, in charge, I think the idea was to
isolate the inconsistent non-DRB RBridge as much as possible.

> the DRB still appoints VLAN forwarders."

There's no difference between the DRB just deciding to act as
Appointed Forwarder for one or more VLANs and the DRB "appointing
himself as appointed forwarder". The DRB is in charge of the link. The
DRB can always decide to be Appointed Forwarder for one or more VLANs
as long as those VLANs are enabled on the DRBs port and that port is
not configured as a trunk port. (Although it would generally work for
the DRB to act as appointed forwarder for a port it was marking as a
trunk port. The end stations don't normally understand TRILL Hello
flags. It would just be inconsistent.) The state of the access bit in
the DRB's Hellos doesn't make any difference to whether or not the DRB
can act as Appointed Forwarder.

> Rakesh

Hope the above helps.

Thanks,
Donald
=============================
 Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
 155 Beaver Street, Milford, MA 01757 USA
 [email-masked]

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From: rakesh kumar <[email-masked]>
Date: Wed, 7 Dec 2011 00:50:36 +0530

Hi Donald,
Thanks a lot for your answer it cleared my concepts on access port but
in former lines i referred "VLANs enabled for
end station service at the port" as end-station enabled vlans.
       My understanding is - "Enabled vlans" are different from "end
station service vlans" and i am considering "end station service
vlans" as always subset of "Enabled vlans".i.e.suppose vlans 1,2,3,4,5
are enabled vlans on port  of rbridge then out of 1,2,3,4,5 vlans only
2,3 can be configured to be "end station service vlans" and Appointed
forwarder will be appointed only for vlan 2,3 as they are "end station
service vlans" .

Please correct me if my understanding is wrong.

Regards,
Rakesh

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From: Donald Eastlake <[email-masked]>
Date: Tue, 6 Dec 2011 15:39:57 -0500

Hi Rakesh,

> Please correct me if my understanding is wrong.

That sounds right.

Thanks,
Donald