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Redundancy using fiber to connect "multi-site"

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Occasional Contributor

Redundancy using fiber to connect "multi-site"

 Hello everyone,

I'm actually struggling with the configuration of a couple of switches we bought earlier this year.


For now, this is a depictation of our network.  You can see it's composed of different mixed switches (3COM and HP for the main part).  You can also see, the red dotted links between switches are fiber connexions.  those connexions are set up using SFP or SFP+ connectors.  The fiber connexion between 3COM and HP 1920 is a link set up in early 2000, and the other one, is set up in october last year (a 10gbps uplink is available and tested).

In order to improve the interconnexion between our two buildings, I would like to use the newer fiber (set up between the two 1950 switches).  The switches are actually configured as depicted up there, but, when I put the fiber link up between 1950's, the network crashes (I suppose due to a loop).

I suppose I've got to setup something like STP (Spanning Tree Protocol) but, the options are so ambiguous that I got no clue on what to configure, where, or even how. The only STP options / modes available on the 3COM switch are STP and RSTP.  And the only thing I find on the 1920 swtich is something called "Loop Protection"

Some ports are excluded in the older switch config, but no clue on how to exclude a port from VLAN1 on the 1950 series.

Just a little more infos.  The top left switchs (1950), is a 3 switches stack (IRF mode).

So, can someone tell me, how I can setup a "redundant" fiber connexion, making the newer one the "main" connexion ? How I can configure STP to work properly ?

In advance, I want to thank all the people who are going to help me find a solution to this issue.

Greatings from Belgium.

Respected Contributor

Re: Redundancy using fiber to connect "multi-site"


Spanning-tree is indeed what you need.

Normally you should be able to enable STP on all those type of switches. 

You should think about which switch you want as root switch in the STP tree, first. As this will be important for the best path calculation. Later it is still possible to modify the cost for each link seperatly.




Honored Contributor

Re: Redundancy using fiber to connect "multi-site"

Loop protection isn't spanning tree. (You should enable Loop Protection on all Access ports and not on uplink ports, but that's a lower priority configuration item you should worry about later).

All your switches should support RSTP, so have a read of the switch manual so you understand how to configure switch priorities and port priorities so you can tell STP to block the old link instead of the new one.

As far as excluding a VLAN from an uplink - this shouldn't be difficult, just don't assign the VLAN to that port.

Occasional Contributor

Re: Redundancy using fiber to connect "multi-site"

Hello Vince,

Back from a week holiday, I tried it all out this morning, and everything seems to work just fine.

I setup the 2 1950 switches with the RSTP.  I change the priority of the top left one to 4096, I used a ssh connection and entered the xtd-client-mode because I was unable to find the option in the web interface.  I also setup RSTP on the 3COM switch.

But one important thing to notice, the bottom right switch, is not a 1920, it's an 1810G - 24 GE, and therefor, unable to use RSTP. But it seems the 3COM switch is doing the job just as fine as needed.

Once again, thank you both for your help.

I'm going to take a deeper look on all the config and try to optimise it a much as possible.  I also want to try the fiber failure, see what's going to happen. I guess we can say this case is closed.