Re: [rbridge] Can someone explain Multi-Topology...its purpose, use, etc?

[Radia Perlman <[e-mail]>]

That's what I'd assume....that you'd lose DCB functionality on links
in which the switches don't do DCB.  So, if a link doesn't do
pause/resume (priority based flow control), then packets might
experience congestion loss on that link.   And the other thing in
DCB...congestion notification.... the switch that doesn't support it
wouldn't inform the source.

I like that feature of DCB...that it can be phased in...not every
switch needs to support it.

Radia



On Wed, Mar 7, 2012 at 2:06 PM, David Klebanov <[e-mail]> wrote:
> Hi Donald,
>
> I wanted to comment on your reply here. In the context of TRiLL or any other
> Ethernet encapsulation technology, how do you deal with intermediate nodes
> that do not support DCB, but yet run TRiLL. Will you basically "loose" DCB
> function on that link inside the TRiLL environment?
>
> Thanks,
> David
>
>
> On 3/2/12 12:23 PM, "Donald Eastlake" <[e-mail]> wrote:
>
>> Some people think congestion notification (CN) is important and some
>> think it isn't.
>>
>> If you are just talking about Priority Based Flow control (PFC, aka
>> "per priority pause") or just PFC and ETS, they are down in the
>> queueing control at ports and orthogonal to what sort of switch
>> protocol you are running above the ports. Could be a bridge, a layer 3
>> router, an RBridge, or whatever. PFC and ETS are pretty much the same.
>>
>> Thanks,
>> Donald
>> =============================
>>  Donald E. Eastlake 3rd   [phone] (cell)
>>  155 Beaver Street, Milford, MA 01757 USA
>>  [e-mail]
>>
>> On Fri, Mar 2, 2012 at 2:48 PM,  <[e-mail]> wrote:
>>> That was a timely submission.
>>>
>>> My understanding is that while congestion notification was originally part of
>>> DCB, that's
>>> no longer considered to be the case.  Deployments of DCB Ethernet for FCoE
>>> typically do
>>> not include congestion notification.
>>>
>>> Thanks,
>>> --David
>>>
>>>> -----Original Message-----
>>>> From: Donald Eastlake [mailto:[e-mail]]
>>>> Sent: Friday, March 02, 2012 2:39 PM
>>>> To: Black, David
>>>> Cc: [e-mail]; [e-mail]
>>>> Subject: Re: [rbridge] Can someone explain Multi-Topology...its purpose,
>>>> use, etc?
>>>>
>>>> On Fri, Mar 2, 2012 at 1:21 PM,  <[e-mail]> wrote:
>>>>> Note that using FCoE over TRILL essentially requires that TRILL support DCB
>>>>> Ethernet.
>>>>
>>>> See https://datatracker.ietf.org/doc/draft-eastlake-trill-rbridge-dcb/
>>>>
>>>> Thanks,
>>>> Donald
>>>> =============================
>>>>  Donald E. Eastlake 3rd   [phone] (cell)
>>>>  155 Beaver Street, Milford, MA 01757 USA
>>>>  [e-mail]
>>>>
>>>>> Thanks,
>>>>> --David
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: [e-mail] [mailto:[e-mail]] On
>>>>>> Behalf Of Thomas Narten
>>>>>> Sent: Friday, March 02, 2012 8:26 AM
>>>>>> To: Radia Perlman
>>>>>> Cc: [e-mail]
>>>>>> Subject: Re: [rbridge] Can someone explain Multi-Topology...its purpose,
>>>>>> use, etc?
>>>>>>
>>>>>>> 3) Specifically for TRILL, why would multi-topology be useful?
>>>>>>
>>>>>> Disjoint multipathing for FCoE. Today, many FC deployments use
>>>>>> physically replicated SANs. Twice the cabling/cost/etc.
>>>>>>
>>>>>> But, there is real value in terms of fault isolation in having
>>>>>> completely disjoint paths.
>>>>>>
>>>>>> TRILL, today, does not really do this.
>>>>>>
>>>>>> Thomas
>>>>>>
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