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General networking question

Q4U
Occasional Advisor

General networking question

I have a network spread over a 600,000 sq/ft plant.  It is pretty sparse, with only about 200 nodes.  It is supported by unmanaged Procurves.  Even though they are Gigabit, and connected by fiber, the performance is sluggish.  Currently the netmask is 255.255.0.0.  Would I get any performance boost if I were to narrow that down quite a bit?

 

Thanks.

3 REPLIES
lanman_4
Occasional Visitor

Re: General networking question

What servers are you running? Workstation O/S?

tschaps
Valued Contributor

Re: General networking question


Q4U wrote:

I have a network spread over a 600,000 sq/ft plant.  It is pretty sparse, with only about 200 nodes.  It is supported by unmanaged Procurves.  Even though they are Gigabit, and connected by fiber, the performance is sluggish.  Currently the netmask is 255.255.0.0.  Would I get any performance boost if I were to narrow that down quite a bit?

 

Thanks.


I doubt it, though I am not an expert on it. As I understand it, the netmask determines the size of the "potential" broadcast domain. The actual size of the broadcast domain is determined by the number of hosts/nodes in it. There is just one broadcast address, regardless of the netmask, and the 200 nodes need to process each packet sent to that broadcast address, and so the quantity of nodes broadcasting is the determining factor in efficiency, not the netmask.

 

If you have an application or process which pings all the IPs in a subnet, that might be significantly slower in a 255.255.0.0 (or /16, ~65k IPs) vs. a 255.255.255.0 (or /24, 254 IPs) network, but I don't believe it's likely that is the cause of overall sluggishness (I run a lot of /16, it's not been a problem) . I think your time would be better spent running some iPerf tests between nodes on different switches to look for bottlenecks-- it could be bad fiber links, too. With unmanaged switches, your options are limited in troubleshooting, but you should be able to tell by the lights on front the speed the fiber is connecting, and doing some iPerf testing, you may find a weak link in the chain slowing the whole thing down.

 

Good luck, please report on progress.

 

 

John Gelten
Regular Advisor

Re: General networking question

First thing I would do...

plug in my laptop at a random switchport, make sure I have no 'chatty applications' on this laptop.

Fire up wireshark and see if there is a lot of unsollicited traffic coming my way. Now, you need to see things like LLDP/CDP and STP related packets as these are generated by the switch on every port, you will also see ARP-related broadcasts, and a multicast packet every now and then, depending on the the topology of the network and the OS and applications connected to it.

 

In an average network I will see probably a few hundred packets per minute or so. If you see less: great, it has probably been optimized. I have been at networks that were defined 'sluggish' and my poor laptop received over 10,000 packets every minute; as did every other host in the network... That slows down things...

 

If indeed you see a lot of traffic, you need to find out what all that traffic is, and whether you can get rid of it.