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should i segment

I am wondering if it is worth segmenting my network. I have a flat class B 300 node network running over multiple Catalyst 3750 stackable switch stacks on a redundant multimode fiber backbone. I have connected sniffer to the network off of the core routing stack and it did diagnose an overloaded lan segment. We are talking about segmenting the network into 6 seperate class C segments correspoding to floors. I realize there are other factors involved. But i am wondering if segmenting is going to slow the network down as opposed to improve it. I know the advantage of segmenting is to decrease the size of the broadcast domains and so decrease chatter. But the downside may be that packets have to cross more subnets on their way to destinations than with a flat network. Open to opinions on this. Thanks

Hall of Fame Super Silver

Re: should i segment


In terms of network performance flat networks do not scale well. And it sounds like you are bumping into that. I believe that it would be advantageous to segment your network. There would be some decisions to be made about how to do that which would depend on understanding your topology. But if it is a simple segmentation of the network with each floor becoming a VLAN and with each VLAN connecting to the core switches, then traffic from any end station going to any other end station on another floor would go to the core switch, be routed onto the other VLAN and go to the destination. I do not see much performance impact in that. And I do believe that there is performance improvement in reducing the size of the broadcast domain.




Re: should i segment

With todays switches like the 3750's you should see very little performance loss by segmenting and you will reduce the broadcast domain . While 300 nodes on a single segment isn't huge I think it would be a good idea to segment them off . Also if you have a problem on one segment it doesn't affect everyone unless it is a hardware problem somewhere . All packets are switched via hardware asics now so the performance loss should be negligible if not better . Nowadays most performance issues are things like speed/duplex mismatches and improperly configured uplinks etc ... It is a lot easier to troubleshoot a segmented network , go for it .

New Member

Re: should i segment


I am a bit astonished that you have already network problems with 300 nodes. We have a flat network with 365 nodes and the network is used about 10% only. Are you sure that there is no loop somewhere?

Segmenting the network is anyway a good idea and i agree with the others that you will not have much impact in regards to performance.


New Member

Re: should i segment

Advantages of segmenting the network from the flat class B is more for scalability I would say, not just in terms of expanding but in terms of features.

For example, what if 1 of your 300 nodes starts acting up by sending a DoS attack on the network. It would practically affect all 299 other nodes. By creating subnets, you could have mitigated this problem.

If you had to write an ACL to block something or to do policy routing on a flat network, you potentially affect all 300 nodes again.

I'm surprised you haven't seen a broadcast storm or spanning-tree loop yet. Then you will see the light!!

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