Hello
What are your cores switches- A- B ?
Are sites A B running VRRP, HRSP, GLBP etc. between each other?
Are the links between A B higher than link to A C , B C or are they all the same?
"Assuming" Site A is your primary stp root and Site B is secondary stp root and If the switch at site C, it is going to be a switch just to extend the lan from A B
The I would suggest to treat it like a adding a additional access switch to the LAN, However PRIOR to linking this "new switch" to sites A B
On Site switch C
1) give it a management IP address and Default-gateway ( presumably the vip address of the first hop routing protocol- if applicable)
2) change its vtp domain to that of the existing vtp domain running on A B
3) change the vtp mode to transparent and then back to client ( this will reset the vtp revision number to 0)
4) change the stp mode to the exiting stp domain running on A B
5) Change stp bridge priority's for al vlans to a higher value then the STP roots of site A B (but not to high so it becomes higher than that of any additional access switch's running inside site C)
4) create two trunks interfaces and connect to site A B respectively
This way, due to the manually applied stp bridge/cost values between AB,,AC BC STP will block the Lan segment between B C and push traffic between site A C and if to link between A C goes down then traffic will be pushed through B C
Flex links:
You can apply this to the two trunks or L3 interfaces if applicable for a physical connection failure, setting it up like
Link C A active
Link C B backup
or vice versa, however this kind of setup negates any possible chances for future requests of utilising both up links at the same time if the need arises.
C gig0/1-----------A
C gig0/2-----------B
int gig0/1
backup interface gig0/2
( this will drop the gig0/2 adjecency and only be used whrn the primary is down.
sh backup
res
Paul
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Kind Regards
Paul
