Hub group and core switch

Unanswered Question
Nov 22nd, 2007
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Dear Sir,

We have a pair of WS-C3750G-48TS-S and several groups of 3com Hub for a network of 200 users.

We want to setup 3750 as the resilience core switch and let each groups of hub have dual link connect to them.

But as the hub does not run STP and linking the two 3750 together for resilience will create a loops.

Any idea on this?


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Overall Rating: 5 (1 ratings)
michelpe Fri, 11/23/2007 - 04:30
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Connecting the hub to the 3750's will work without any configuration as STP by default is turned on

The 3Com hubs should be transparent so the 3750 should see back it's own BPDU's and thus block one of the links towards the hub and breaking the loop



josephschung Fri, 11/23/2007 - 04:58
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Dear Michel,

Thanks for your idea? Did you try it before? We cannot try it now before we purchase the equipment.


michelpe Fri, 11/23/2007 - 05:01
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Yes, i've seen this used before and it's working fine.



jarredtaylor Fri, 11/23/2007 - 05:55
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This probably goes without saying, but please be sure portfast is disabled on the ports connecting to the hubs.


josephschung Fri, 11/23/2007 - 06:23
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If there are three groups of hubs, so totally six ports on the switch will be sending BPDU together. Eventually, only one of the ports will be left forwarding PBDU and the other five will be blocked. Am I right?

michelpe Fri, 11/23/2007 - 06:36
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If the hubs group of hubs are connected together directly as well yes.

But probably it makes more sense to link each group of hubs directly to the 3750 (not to the other groups).

Then only one port per group of hubs will be blocked.

In anyway how you do it it will work that only one port connected to the hub (or hubs if they are linked together directly) will be Forwarding, the rest will be Blocked


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