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New Member

Redundant links!

Here are the requirements imposed on me, I have devices that need to communicate with each other (about 30 devices), each device connects to two 2950s (one active and one for redundancy). Each 2950 in turn connects to a 4503 (one for the active lan and one for the redundant lan). All the devices share the same subnet, and each device has only one MAC address. The redundant network has to automatically take over if one of the active switches fails. Can STP be used to acheive this? By assigning a different priority on each interface of the redundant network for example. Thank you in advance for any suggestion.

4 REPLIES
Cisco Employee

Re: Redundant links!

If this is a purely layer 2 network then all the switches will be connected by either point-to-point links or trunks. By one subnet I believe you mean having only one VLAN.

Regardless Spanning-tree should be turned on and would ensure redundancy in the network while avoiding any loops in the network. Spanning-tree runs between switches and creates a loop free network topology. Please read more on it at :

http://www.cisco.com/univercd/cc/td/doc/product/rtrmgmt/sw_ntman/cwsimain/cwsi2/cwsiug2/vlan2/stpapp.htm

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/12113ea1/2950scg/swstp.htm

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/12113ea1/2950scg/swmstp.htm

Bronze

Re: Redundant links!

Where do the switched networks (primary and backup) connect to each other? You described them as separate networks. There is only a loop requiring spanning tree if they connect to each other at two points (hence the term loop).

New Member

Re: Redundant links!

The switched networks will connect to each other through a trunk between the 4503s. Each 2950 will connect to a 4503 (primary and backup). It is in reality the same network (same subnet, same vlan). But one swich network is to be used only as a backup in case of failure. Thank for the help.

New Member

Re: Redundant links!

By specifiying root bridge, portvlanpriority you can have one side be the primary.

Choose these parameters carefully and test.

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