STP over wireless bridge as a backup

[carl_townshend]

Hi Guys

We have some cisco 9200 switches, there are 2 connections between them, 1 is a fiber, the other will be a backup link using a ubiquiti wireless bridge.

The bridge has an option to enable STP, my question is what will this do? do we need to enable STP on the bridge? or if its off will it simply relay the bpdu's transparently between the switches?

Also as sometimes wireless can be unreliable, do we need to tune stp at all? 

cheers

[Flavio Miranda]

Hi @carl_townshend 

 STP is meant to avoid loop, right? So, the bridge is only connected to the switch and is not possible to cause the loop.  I dont see why to use STP on the bridge.

 Now, on the switch, if the fiber link is layer2, you can cause a loop as the switch have 2 connection, on this case the STP is required. And yes, the bridge should forward all traffic between switches included STP traffic and the bridge itself does not need to participate on the STP process.

[carl_townshend]

Hi Flavio

We have 2 switches, they are connected directly via fiber, and then we also have an ethernet bridge plugged into each switch for a backup connection, so indeed there is a loop here.

[paul driver]

Hello Carl
Can you post a simple diagram how this is setup please?

[carl_townshend]

[balaji.bandi]

still my post valid :

Layer 2 STP - if you enable you can make fibre as primary by changing the STP Priorities.

check some Tunings :

https://www.ciscopress.com/articles/article.asp?p=2995351&seqNum=2

Other suggestion - if Layer 2 not must convert them to Layer 3, so you can play with IGP between site which link path primary and secondary.

[balaji.bandi]

Layer 2 STP - if you enable you can make fibre as primary by changing the STP Priorities.

check some Tunings :

https://www.ciscopress.com/articles/article.asp?p=2995351&seqNum=2

Other suggestion - if Layer 2 not must convert them to Layer 3, so you can play with IGP between site which link path primary and secondary.

[carl_townshend]

Hi, I think the issue we are worried about and have seen before is where the wifi drops the bpdu's etc and loopguard or udld kicks in.

[Georg Pauwen]

Hello,

if you keep this a layer 2 topology, STP really is the fastest and most reliable 'failover' option. Why would the bridge drop the BPDUs ? Under what circumstances have you seen this happening ?

[carl_townshend]

Wifi is not as reliable as cable, it is a wireless bridge operating over a few hundred meters, weather, trees etc can all play a part in this

[paul driver]

Hello
Yes i would say STP on the L2 bridge is most applicable, you can cost out the STP path to accommodate your preferred l2 switch path but by default switching should take the physical fibre path.