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Existing PVST+ network, connecting some Rapid-PVST switches?

We have an existing PVST+ network with a pair of 4507R's at the core connecting to various Cisco switches (2950's, 3560's & 3750's). The whole thing is a bit of a mess in it's structure but will gradually be phased out over the next few months.

We are building a new network comprised of two Catalyst 6509-E's with Sup720's and 10GE ports in the core and Layer-3 to the edge using Catalyst 4948-10GE's. The whole design is Layer-3.

Our original intention was to connect the 6509's to the old network using routed /30 connections, unfortunately the customer will not re-address servers until later on but wants to move them onto the new infrastructure now. The majority of the servers are currently on a single VLAN - VLAN 1. To maintain this legacy connectivity we have to allow a single VLAN (VLAN 1) to span from the old network to the new one. To do this we created two trunks allowing this legacy VLAN plus a routed /30 VLAN (switchport trunk allowed vlan 1,500). When these trunks were initially connected we saw OSPF form an adjacency and we saw forwarding for the legacy VLAN (roots are in the old network). The following day however the customer reported intermittent 'lock-ups' on work stations and servers, since we weren't on site to investigate the issue the new connections were disconnected and the problem seems to have gone away.

We have connected other switches into the old network and not seen this happen before. However we are running Rapid-PVST on the new core and PVST+ on the old network. Is this likely to be the cause and if so where do we start looking?



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Re: Existing PVST+ network, connecting some Rapid-PVST switches?

In this try using same PVST modes in both the networks and see if the problem occurs.To switch between PVST+, Rapid PVST, , use the spanning-tree mode command.Refer the following URL for more info

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