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STP convergence / EtherChannel b/w Cat4000s connected using WirelessBridge

One of my customers has a Cat4003(with SupII) and Cat4006(withSupIII) at a distance of about 1 KM.

They have two parallel wireless links between them (one using the Cisco AiroNet 350 Series wireless bridge at both ends and other one using Non-Cisco InfraRed link) as follows:


4003| |4006


There are other 3524 switches behind these Cat4000s at both locations.

The problem is that one of the links remains blocked due to Spanning tree. Whenever the primary link fails it takes about 30 seconds to switchover to the other link.

Is it possible to simultaneously use both of these links by creating EtherChannel or some other means; So that even if one of the links stop functioning, the other one will be there and switches won’t lose the connectivity.

If EtherChannel is not possible, Can I play with some other timers or features to make the switchover happen quickly.

I would highly appreciate any help in this regard.


Ahmer Ghazi


Re: STP convergence / EtherChannel b/w Cat4000s connected using


to make a final design there is necessary to answer:

I suppose these InfraRedDevices are L1 devices? I.e., they don't participate in STP?

How many VLANs are used on that lines (I suppose ony one VLAN)?

What is the STP network diameter?

Where is the STP root?

But I'm afraid there is not possible to use EtherChannel - it required direct connection between the switches, all lines the same speed, duplex, VLANs allowed.

I don't see any possibility to speed up the STP convergence (maybe just decreasing STP parameters if the network diameter were minimal, but it doesn't seem so) because from the 4000s point of view the link failure is always indirect. So UplinkFast won't help. Maybe BackboneFast enabled on the 4000s would help, but it's a little dangerous because 3524 don't support BackboneFast (it's possible not to enable it on every switch but it depends on the topology).

So the only solution I see is to involve some L3 devices and run a fast-convergence dynamic routing protocol on the parallel lines (OSPF, EIGRP, e.g.). It should also enable load balancing over both lines and thus using all bandwith available.