LinuxQuestions.org - Moved from a class C to Class B network

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Moved from a class C to Class B network - Performance hit?

I also recently (read last sunday) redesigned the ip scheme. In order to bring some order to the ips we were using i moved from a class C to a Class b (255.255.0.0) so I could do things like ...

Servers 10.0.1.X
Printers 10.0.2.X
DHCP 10.0.3.X
Wireless 10.0.4.X

Well you get the idea. This brought some natural order to things and made setting up content and firewall rules very easy since blocks of ip's can be used. Now I have noticed a performance decrease when one segment (10.0.X) is trying to talk to another (10.0.Y). There are less than 200 devices on the network so its not a ton. Is the performance hit do to broadcasts having to be sent out to a much larger ip range now even though devices are not using all the ips?

Suggestions, thoughts. What can I do to prevent the performance degrade, should I just go back to class C network?

Paul Kraus

Also would it make a difference if segments were on their own switches or would that do nothing?

Quote:

Originally Posted by pkraus109 (Post 3815468)

i moved from a class C to a Class b (255.255.0.0) so I could do things like ...

Servers 10.0.1.X
Printers 10.0.2.X
DHCP 10.0.3.X
Wireless 10.0.4.X

Now I have noticed a performance decrease when one segment (10.0.X) is trying to talk to another (10.0.Y).

Hi Paul, I don't imagine you should see much of a performance decrease with a class B. Question though: how do you have your subnets set up? Are they 255.255.255.0 or 255.255.0.0? What is the gateway for each "segment", or do you have one gateway no matter if it is a server/printer/anything?

The subnet is 255.255.0.0 and the one gateway is 10.0.0.1

Quote:

Originally Posted by pkraus109 (Post 3815592)

The subnet is 255.255.0.0 and the one gateway is 10.0.0.1

Hmmm, it shouldn't be an issue then. Is it just two pieces of equipment that are talking to each other slowly? Or every piece of equipment on that subnet?

The way it should be working (with some made up IP addresses):

Code:

10.0.1.5 wants to talk to 10.0.4.4

10.0.1.5 looks at its own subnet mask and sees that it is 255.255.0.0

10.0.4.4 fits into its subnet of 10.0.x.x

So, it sends out an arp who-is request ("who-is 10.0.4.4") broadcast

10.0.4.4 hears the who-is broadcast and responds to 10.0.1.5 ("arp response: 10.0.4.4 is at 00:11:22:33:44:55 mac address")

10.0.1.5 puts the correct mac address as the destination as it creates the packet and sends it out.

The level 2 switches send it to the destination machine (they don't care less about IP addresses)

10.0.1.5 remembers the MAC <-> IP address association so it doesn't have to ask for future packets.

I was thinking that maybe one of your subnet masks was set wrong so that it had to send every packet to the gateway. But if you've got everything set up right, I don't see why there would be a problem.

Does it seem to only be every segment having the problem?
Another thought: are your switches "smart" level 3 switches that are looking at the IP addresses of the packets and have default gateways programmed into them as well?

We are not using managed switches and it appears to be everything. What exactly does a smart switch do?

Quote:

Originally Posted by pkraus109 (Post 3816180)

We are not using managed switches and it appears to be everything. What exactly does a smart switch do?

Depends on the smart switch. They can look at IP addresses and apply VLAN flags or different things. In essence, they start to do a few functions that a router is made to do.

As for your slow problem, that's strange that it's not working. So if you take two computers and put them on the same segment they can talk to each other fast, no problems. But as soon as you move one to a different segment it slows down? Even if you just leave it plugged in physically where you had it?