In order to provide a higher throughput link we want to connect our core switch to a company we are integrating with over a 4 gig trunk. However they run RSTP on thier LAN and so do we. I think we will run into issues with this when the trunk comes up between our core switch and theirs.
Has anyone got any advice on what issues may occur and if there is a way around keeping each companies current RSTP 'domain' separate until the companies are fully integrated on to one LAN. (This is meant to be an interim solution while their infrastructure and users are moved onto our kit, the current connection is via a routed firewall connection to their network so hoping to replace this with a switch to switch 4 gig trunk as we're now physically in the same building with the company merger that has happend).
There is a facility called BPDU Filter that is intended for situations like these. The BPDU Filter efectively stops both sending and receiving BPDUs on a selected port, thereby creating a boundary between two RSTP domains. Of course, this link is not protected against Layer2 loops anymore so it is up to the network administrator to make sure that there are indeed no redundant connections between the two RSTP domains.
You can activate this feature simply by writing spanning-tree bpdufilter enable on the respective port. You have indicated that you are using a 4 gig trunk - I assume you have created an EtherChannel. That command would then be placed on the Port-channel interface.