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New Member

STP

Hi,

my network is a star topology consisting of the main switch connected to 10 switches.there the is no loop in the network.

is it necessary to have the main switch as the root?

which spanning-tree protocol is recommended to be enabled on all switches in this case ?

thank you,

1 ACCEPTED SOLUTION

Accepted Solutions
Super Bronze

Re: STP

Exactly correct.

Might add, you make at least a two link Etherchannel from the edge switch where connected to different 3750s or different line cards in a chassis. This avoids single point of failure for the connection to your "core". As for redundancy of the rest of the core device, 3750 stacks will continue to function with loss of one member, chassis needs to support dup sups, etc.

6 REPLIES
Hall of Fame Super Blue

Re: STP

It would definitely make sense to have the main switch as root because

1) if the main switch goes you have lost all switches anyway so there is little point in having one of the others as root.

2) You would get some horrible L2 paths if one of the spoke switches was root.

As for which one - RSTP if your switches support it. If you have a huge number of vlans MST is worth looking at. Otherwise standard 802.1d would be fine in your topology as you don't have any loops anyway.

By the way for loops you could also read redundancy. With your topology everything really does rely on the main switch.

Jon

Super Bronze

Re: STP

If you have no loops, you don't really need to use STP. However, it's still often worthwhile having in case you accidentally patch a loop.

Jon's post touched on redundancy and your critical root switch. You might want to consider installing a second root switch so that you don't have a single point of failure for your whole network. If you install one, now you'll will have loops and a STP variant will be needed (and as Jon also suggested, try to use a RSTP variant). Define your "better" root switch as the primary root and the other root switch as the secondary root.

PS:

The "better" root switch might be one with more performance and/or with Etherchannel links to your other edge switches.

PPS:

If your root switch was chassis, or 3750/3750-E stack, you can have redundancy of the root device without, perhaps, needing STP. However, I suspect such root devices might be way beyond your budget.

New Member

Re: STP

Hi Jon, Joseph

thank you for your clarification.

actually I have actually configured the main switch as the root bridge. just wanted to know the impact of not having it as root since there is not loop in the network and no need for STP unless of course accidentally someone patched a loop.

joseph,

can you please elaborate more on the idea of having redundancy of the root device without the need of STP.

thank you

Jean

Hall of Fame Super Blue

Re: STP

Jean

What Joseph means (Joseph, please correct me if i am wrong) is that if you used 2 3750 switches stacked then they are in effect treated as one virtual switch so by adding a second root switch you still do not need to use STP ie. you would still have a loop free but now redundant topology.

A chassis based switch could also be used with redundant supervisor eg. certain 4500 swithes or 6500 switches but these are expensive.

Jon

Super Bronze

Re: STP

Exactly correct.

Might add, you make at least a two link Etherchannel from the edge switch where connected to different 3750s or different line cards in a chassis. This avoids single point of failure for the connection to your "core". As for redundancy of the rest of the core device, 3750 stacks will continue to function with loss of one member, chassis needs to support dup sups, etc.

New Member

Re: STP

thanks Guys!

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