[j-nsp] Connecting two spanning-tree domains

[Marvin Bartchlett]

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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