[j-nsp] Connecting two spanning-tree domains

[joel jaeggli]

On 8/27/13 8:16 AM, Johan Borch wrote:
> This is basically two datacenters with a lot of devices on each side, and I
> need to exchange vlans in a redundant way. I need something solid so that
> one side can't interfere with the other side. Is there some way to add an
> extra L2 device between the networks to act as some kind of spanning tree
> "firewall" ;) talking MSTP and RSTP but not changing the root on either
> side?
>
You've arrived at a point where spanning tree may be running out of
steam, depending on your choice of platforms you should probably be
looking at trill/spb/L2vpn to glue these together. at some pooint you're
also going to want to use all your paths rather than blocking some of
them to build a loop-free topology.
> Regards
> Johan
>
>
> On Tue, Aug 27, 2013 at 4:20 PM, Marvin Bartchlett
> <mbartchlett at juniper.net>wrote:
>
>>  You will have to be very careful. If I’m not mistaken MST actually uses
>> CST to tie together the multiple spanning tree instances running in MST. If
>> you tie in a Cisco device running RSTP the Juniper and Cisco devices will
>> default to CST on those links since that’s the common ground (as Johan said
>> below).
>>
>> This will trigger a spanning-tree root election on your CST instance -
>> depending on how you have things configed you may endup with different
>> roots. This could effect the flow of your MST instances that rely on CST.
>>
>>  Best regards,
>> Marvin Bartchlett
>> Juniper Networks
>> Resident Engineer - City of Lakeland, FL
>> Mobile: +1-904-614-1712
>> Skype & Google+: mbartchlett
>>
>>  *From:* Ge Moua
>> *Sent:* Tuesday, August 27, 2013 9:35 AM
>> *To:* Johan Borch
>> *Cc:* juniper-nsp at puck.nether.net
>>
>> This is a juniper forum so I apologize ahead of time for the vendor-C
>> reference below (but standards-based L2 works mostly the same across all
>> vendor implementations):
>>
>> https://supportforums.cisco.com/thread/344842
>>
>> --
>> Regards,
>> Ge Moua
>> Univ of Minn Alumnus
>> --
>>
>> On 08/27/2013 08:16 AM, Johan Borch wrote:
>>> Will that mean that I still have two roots, one in each network and
>>> that they don't affect each other?
>>> Regards
>>> Johan
>>>
>>>
>>> On Tue, Aug 27, 2013 at 2:53 PM, Ge Moua <moua0100 at umn.edu
>>> <mailto:moua0100 at umn.edu>> wrote:
>>>
>>>     IIRC once joined, the MST and r-pvst L2 domains will speak CST (as
>>>     a common denominator).   You may want to consider pruning vlans
>>>     where only needed (esp if you have a high vlan count on either or).
>>>
>>>     --
>>>     Regards,
>>>     Ge Moua
>>>     Univ of Minn Alumnus
>>>     --
>>>
>>>
>>>     On 08/27/2013 03:56 AM, Johan Borch wrote:
>>>
>>>         Hi!
>>>
>>>         I need to connect two spanning-tree domains, one is running
>>>         MSTP and one is
>>>         running rapid-pvst. Is this doable? The two networks have
>>>         different roots
>>>         and it needs to stay like that but I still need redundant
>>>         links between
>>>         them. I need to transport VLANs from one network to the other
>>>         and only one
>>>         side support MPLS.
>>>
>>>         Ideas? :)
>>>
>>>         Regards
>>>         Johan
>>>         _______________________________________________
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>>>
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