Subject: [rbridge] Queries on RFC 6325 - Default port type

From: Abhinav Bhatia <[email-masked]>
Date: Tue, 13 Dec 2011 13:30:09 +0530

Hi ,

I looked at some of the posts and RFC, there is confusion on the default
settings to the trill port. According to RFC it seems the default settings
is both access and trunk bits are 0.
In this mode port will do both encapsulation/decapsulation and forward the
trill data packet. If yes the what should be the behaviour when both the
bits are set.

>From rbridge Digest, Vol 91, Issue 4

*" 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."*
**
Does above bold statement means only trunk port or does it include both
"trunk and access bit set 0"?

Regards,
Abhinav
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---

From: Donald Eastlake <[email-masked]>
Date: Tue, 13 Dec 2011 09:28:16 -0500

Hi Abhinav,

On Tue, Dec 13, 2011 at 3:00 AM, Abhinav Bhatia
<[email-masked]> wrote:
> Hi ,
>
> I looked at some of the posts and RFC, there is confusion on the
> default settings to the trill port.

I don't think I'm not confused.

> According to RFC it seems the default settings is both access and
> trunk bits are 0. In this mode port will do both
> encapsulation/decapsulation and forward the trill data packet.

That's right. By default RBridge ports are universal ports. This is
motivated by the TRILL goal of supporting zero/minimal configuration.

> If yes the what should be the behaviour when both the bits are set.

I don't see why you have a question on this. The dominant, longest,
and most complete section of RFC 6325 on these port bits is clearly
Section 4.9.1. There, the bits are called the "TRILL traffic disable
(access port) bit" and the "End-station service disable (trunk port)
bit". While it seems a bit silly to turn on both of these bits instead
of just turning on the "Disable port bit", I don't see any conflict
between these two bits. The access port bit is defined in terms of its
effect on the transmission and receipt of TRILL IS-IS frames and the
trunk port bit is defined in terms of its effect on the transmission
and receipt of native frames. These are disjoint classes of frames.

> "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."
>

Sorry, perhaps my wording was not as pedantic as it should have been.
"not an access port" means "has the TRILL traffic disable (access) bit
set to zero" and "is an access port" means " has the TRILL traffic
disable (access) bit set to one". Neither assertion has anything to do
with the value of the trunk bit.

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

---

From: Radia Perlman <[email-masked]>
Date: Tue, 13 Dec 2011 09:36:04 -0800

A shorter answer is that if both bits are on, the port is disabled.

Radia

---

From: Donald Eastlake <[email-masked]>
Date: Tue, 13 Dec 2011 14:53:49 -0500

Hi Radia,

> A shorter answer is that if both bits are on, the port is disabled.

That's almost true except that setting both bits will have no effect
on port processing of Layer 2 control frames and still allows the
transmission and receipt of Hellos. On the other hand, setting the
disable bit for the port normally disables all types of frames.

Thanks,
Donald