[rbridge] Consensus Check: C-Tags

[Dinesh G Dutt]

I agree with all points that Eric makes here. Consider the following 
scenarios:
- Rbridges are used within the provider backbone that isn't interested 
in doing much with ISIDs
- Rbridges are used within the enterprise but using S-Tags to carry the 
DEI bit.

I understand that there are complications if you attempt to mix C-Tags 
and S-Tags. That is why I'm fine with Rbridges stating that they're 
talking about C-Tags only. I don't want it to explicitly state that 
S-Tags are prohibited.

As Caitlin pointed out in an earlier email, STag is merely the ethertype 
to carry the VLAN info (same size, 12b since that is how big the field 
is in the Stag as well)

Dinesh
Eric Gray wrote:
> As a response to the general question - together with a response to
> the follow-on response so far - I would like to make the following
> points:
>
> 1) I am very uncomfortable with explicitly limiting the applicability
>    of RBridges to the case where "Enterprise" is defined specifically
>    to exclude service provider networks (remember that an SP is also
>    an "Enterprise" - unless explicitly excluded).
> 2) I agree with Dinesh that we should not explicitly exclude S-TAGs,
>    even though it is (as Donald points out) necessary to be specific
>    in a protocol specification.  A key reason for this is that - in
>    the case where a SP might want to use RBridges to support their
>    own use of an Ethernet (or Ethernet-like) infratructure (which 
>    very-well might include both C-TAGs and S-TAGs).
> 3) One way to get around this is to state - up-front - that the use 
>    of C-TAGs is assumed in the protocol specification, but there is 
>    no intention to prohibit use of S-TAGs, and probably further say
>    that any additional specification required to support S-TAGs is
>    out of scope in this protocol specification.
> 4) The concerns expressed by Caitlin are not - and should not be -
>    relevant to the protocol specification (especailly if scoped as
>    I suggest above), since they are very explicitly related to an
>    implementation (or assumptions about implementations) that may
>    not be true for every implementation, and could very well be
>    avoided entirely by simply making the implementation choice to
>    onyl support C-TAGs.
>
> --
> Eric Gray
> Principal Engineer
> Ericsson  
>
>   
>> -----Original Message-----
>> From: rbridge-bounces at postel.org 
>> [mailto:rbridge-bounces at postel.org] On Behalf Of Eastlake III 
>> Donald-LDE008
>> Sent: Monday, April 07, 2008 10:16 PM
>> To: Dinesh G Dutt
>> Cc: Rbridge at postel.org
>> Subject: Re: [rbridge] Consensus Check: C-Tags
>>
>> Hi Dinesh,
>>
>> I'm not sure exactly what you mean by "explicitly prohibit the use of
>> S-tags" but wherever the protocol spec requires a VLAN tag (Outer or
>> Inner), it currently specifies the use of the C-tag Ethertype. 
>>
>> It is my impression that people are thinking that the current protocol
>> spec is for customer Rbridges and that, perhaps, at some point in the
>> future a separate "provider Rbridge" document could be written which
>> talks about S-tags, etc.
>>
>> Thanks,
>> Donald
>>
>> -----Original Message-----
>> From: Dinesh G Dutt [mailto:ddutt at cisco.com] 
>> Sent: Monday, April 07, 2008 9:26 PM
>> To: Eastlake III Donald-LDE008
>> Cc: Rbridge at postel.org
>> Subject: Re: [rbridge] Consensus Check: C-Tags
>>
>> I'm fine with stating only about C-tags and not mention 
>> anything about 
>> S-tags. I wouldn't want the spec to explicitly prohibit the use of
>> S-tags.
>>
>> Dinesh
>> Eastlake III Donald-LDE008 wrote:
>>     
>>> This is a check via the mailing list to confirm or refute 
>>>       
>> an apparent
>>     
>>> consensus at the Philadelphia meeting:
>>>
>>>
>>> ******* The TRILL Base Protocol draft should only mention 
>>>       
>> and use IEEE
>>     
>>> 802.1 C-tags. It should not mention or use S-tags, except 
>>>       
>> possibly to
>>     
>>> distinguish them from C-tags, state that they are not used, or the
>>>       
>> like.
>>     
>>> If no particular controversy arises over this in the next two weeks,
>>>       
>> We
>>     
>>> will declare it to be the working group consensus.
>>>
>>> Thanks,
>>> Donald & Erik
>>>
>>> _______________________________________________
>>> 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
>>
>>
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>>
>>     
>
>   

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