[c-nsp] VPLS, spanning tree and redundancy

[Enno Rey]

Hi,

just a question in advance: do you know for sure that STP BPDUs are forwarded "across the cloud"?
[this may or may not be the case, depending on the gear used and the configuration/carrier (you?) providing the VPLS links]


On Tue, Mar 25, 2008 at 09:47:16AM +1300, Pshem Kowalczyk wrote:
> Hi,
> 
> It looks like one of our customers would like to have redundant L2
> access. We have two PEs in both locations so in theory that should
> work. However, I wonder what your  ideas are about preventing L2 loops
> in such network. The customer envisaged something like this:
> (variable-width font):
> 
> CSW1----CSW2
>    |            |
> PE1       PE2
> 
>  MPLS cloud
> 
> PE3        PE4
>    |             |
> CSW3---CSW4
> 
> where CSW is the customer's switch. Currently they only have one half
> of that solution (CSW1, PE1, PE3 and CSW3) with a single VPLS between
> PE1 and PE3.
> 
> The solution we came up with is to run single VPLS1 between PE1 and
> PE3 (the way it is now) and then add VPLS2 between PE2 and PE4. This
> way customer can run spanning tree

if I understood you correctly there will be two different "VPLS clouds" between both pairs of CSW/PE links?
why run STP at all, then?






 (bearing in mind that if they set
> the cost incorrectly they will get CSW3 talking to CSW4 through CSW1
> and CSW2).

again: given two different clouds this shouldn't happen.


furthermore I seem to recall a Cisco white paper discussing ways (though impractical ones, from my perspective) to avoid loops in VPLS scenarios:
http://www.cisco.com/en/US/tech/tk436/tk891/technologies_white_paper09186a00801f6084.shtml


thanks,

Enno


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