[rbridge] Ingress Rbridge and FTAG again

[Caitlin Bestler]

rbridge-bounces at postel.org wrote:
> Silvano Gai wrote:
>> Joe,
>> 
>> Let's summarize what we are asking:
>> 
>> 1) today proposal has ingress RBridge address and egress RBdridge
>> address, but they are not carried both in the same frame. The first
>> request is to always carry both. I have hard time thinking that this
>> requires a change in the WG charter.
> 
> It does because they are required to support capabilities not
> indicated in the charter, namely traceroute.
> 

There is at least one justification that is in scope: namely that
a core RBridge that also supports 802.1au (congestion avoidance)
would benefit from having the source rbridge so that it could
properly encapsulate its BCN response without requiring a lookup
delay.

I am not convinced that the number of cases where this will be
relevant justifies the extra field -- but including to enable
this case would clearly be in scope.

One reason I currently do not estimate this as a worthwhile
feature is that I believe that the ingress and egress rbridge
will be a majority of the rbridges that any given packet 
traverses. But my perceptions are biased towards the edges
and the working group could come to a different assesment.

Without the source rbridge in the shim header there IS a
negative impact on an 802.1au bridge generating a BCN.
Is that not enough to make this an item to be considered?