[rbridge] base protocol minor rewording issue -- 4.4.1.1 bullet 3

[Dinesh G Dutt]

Hi Donald,

Consider the following figure:
                                  | --- RB3 -- B
A --- RB1 --- RB2 +|
                                  | --- RB4 -- C

If in the shared segment between RB2-RB4, if RB2 is the designated 
forwarder, and a frame is sent from C to B, according to the wording of 
bullet 3, Outer.MACDA is set to RB2 and MACSA set to RB4. This doesn't 
work for the reasons you'll see if you follow the logic through. Even if 
it did work, I dislike the frame flow. I think the Outer.MACDA must be 
set to RB3.

This is what I'm trying to say. Did I read that section wrong ?

Dinesh
Donald Eastlake wrote:
> See below:
>
> On Fri, Oct 10, 2008 at 8:18 PM, Dinesh G Dutt <ddutt at cisco.com> wrote:
>   
>> That doesn't work correctly either. You want to distinguish two separate
>> cases:
>> - The destination Rbridge is known to be local to a link VS
>> - The destination Rbridge is not local to that link and RB1 is not the
>> designated forwarder for that link
>>     
>
> I don't understand your case descriptions above.
>
> This bullet appears after two other bullets. (By the way, you only get
> to this part of the text on receipt of a native from on a port where
> RB1 is the appointed forwarder for the frame's VLAN.) The first bullet
> says that if the destination is known to be on the same link, the
> RBridge just discards the frame because the destination has already
> gotten it. The second bullet says that if the destination is on
> another link out of RB1 where RB1 is appointed forwarder for the
> frame's VLAN you forward the frame in native form. This is the third
> bullet where the destination is on a link for which another RBridge is
> appointed forwarder for the frame's VLAN so you have to encapsulate
> it.
>
>   
>> In the former case, you send the frame to RB2 directly (outer.MACDA is RB2)
>> and in the latter case, you send it to the designated forwarder (outer.MACDA
>> is RBm).
>>     
>
> If you are just trying to say the text should have four cases by
> splitting the encapsulation case into one where the egress RBridge
> happens to be one RBridge hop from the ingress RBridge and a
> "different" case where the egress RBridge happens to be multiple hops
> from the ingress RBridge, I see no need to do that. If RB1 and RB2 are
> one hop apart, then the next RBridge hop towards RB2 from RB1 is RB2.
>
> Thanks,
> Donald
>
>   
>> Dinesh
>> Donald Eastlake wrote:
>>     
>>> It certainly is a run on sentence and it should be re-worded. But now
>>> that there is no pseudo-code in the base protocol draft, I think the
>>> specification needs to be fairly complete here. Your suggested text
>>> leaves out a lot of details but this bullet is in the middle of
>>> Section 4.4 which, to my mind at least, is supposed to give the
>>> details for handling any possible input frame.
>>>
>>> How about:
>>>
>>> If the destination is known by RB1 to belong to egress RBridge RB2,
>>> then RB1 encapsulates the frame with a TRILL header and transmits the
>>> encapsulated frame towards RB2. This TRILL header has M = 0 and
>>> specifies the nicknames for RB1 and RB2 as the ingress and egress
>>> RBridges respectively. The transmitted frame has RB1 as the
>>> Outer.MacSA and the next hop RBridge towards RB2 as the Outer.MacDA.
>>>
>>> Thanks,
>>> Donald
>>>
>>>
>>> On Fri, Oct 10, 2008 at 6:33 PM, Radia Perlman <Radia.Perlman at sun.com>
>>> wrote:
>>>
>>>       
>>>> I can't quite parse bullet 3 in section 4.4.1.1. It might be correct,
>>>> but the wording is confusing.
>>>>
>>>> It's talking about the case where RB1, designated forwarder, receives a
>>>> packet that RB1 knows should
>>>> go to egress RBridge RB2.
>>>>
>>>> Maybe this wording is clearer?
>>>>
>>>> *************section 4.4.1.1 bullet 3
>>>>
>>>> If the destination is known by RB1 to belong to egress RBridge RB2, then
>>>> RB1 encapsulates the
>>>> frame with TRILL header specifying RB2's nickname as egress RBridge, and
>>>> forwards the encapsulated
>>>> frame towards RB2.
>>>> _______________________________________________
>>>> rbridge mailing list
>>>> rbridge at postel.org
>>>> http://mailman.postel.org/mailman/listinfo/rbridge
>>>>
>>>>         
>>>       
>> --
>> We make our world significant by the courage of our questions and by the
>> depth of our answers.                               - Carl Sagan
>>
>>
>>     
>
>
>
>   

-- 
We make our world significant by the courage of our questions and by 
the depth of our answers.                               - Carl Sagan