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PLanning STP and VLAN in a Ring Topology

6 GE switches (with2 GE ports separately) form a ring topology. The GE ports are connected one by one using transparent point to point SDH connections.

Don't know how STP works in such circumstance. How to plan STP and VLAN? Thanks a lot.

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Re: PLanning STP and VLAN in a Ring Topology

This is a rather complicated setup. Is this network already operational?

Is this a LAN or a MAN? Leased lines or private links?

Are you certain that you will not run into some distance-limitations?

Spanning tree will work OK for you if this is a LAN. Just be careful that you choose the correct switch as root-switch. This is normally the one at the data-center. With spanning tree, one link will always be in standby mode.

A more optimal solution might be to implement L3 switching on these links, this allows you to use them all. This is preferrable if you are paying money for each link.

Regarding VLANs; if this is one single LAN, you may run a single VTP domain over it. If it is larger than one building, i.e. a campus-network or a MAN, you should consider splitting it up in separate VTP-domains, one for each entity that uses the network. The links connecting the sites should certainly not be set up as trunks in this case. Just IP routing.



New Member

Re: PLanning STP and VLAN in a Ring Topology

It's a private network being planned. The real toponogy will be three such rings , and these 2layer-switched rings will get converged in a 3layer switch in the data center.

It does cover a large area but the distance limitations are eliminated through SDH transportation. SDH will provide transparent point to point GE connection for those switches.

Geographically, it is a MAN; but functionally, it is LAN with LAN applications running on.

There will be many VLANs. One VLAN may cross many switches at different locations; One switch may contain many VLANs.

So, is it feasible for STP and VLAN implementation, how to make it work and what shoud I pay special attention to during planning?

Thanks a lot.



Re: PLanning STP and VLAN in a Ring Topology

If it is a private network you can do what you want. For myself, I would always advise a customer to opt for layer3 switching in this environment for three reasons:

1: faster recovery in case of failures

2: better load balancing

3: no blocked (idle) links

You can use vlans as well in this config. Look at the Cisco hierarchical model and try to implement this type of switching-block at each location.

I do not know in what degree the money is an issue, but will become an expensive network, a real challenge for the designer!



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