Large subnet, is it a problem really? 1

[pjcarmen]

I'm pondering making some changes to a network I took over a while back. Right now there are 3 networks in different locations 10.10.0.0/16, 10.20.0.0/16, and 10.40.0.0/16. Now with the snm of 255.255.0.0 I have like 65,000 available addresses... that's a lot. In truth each LAN has only 40-80 devices.

Does the large potential host pool have any impact on the network? Should it even concern me?

If I make a change to the subnet, there are a lot of things that need to be re-configured, servers, firewalls, printers, wireless and so on. I don't want to do all that work, if there is no good reason for it.

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"Is it ignorance or apathy? Hey, I don't know and I don't care."
-Jimmy Buffett

 

[North323]

just change the subnet to 255.255.255.0 i would be concerned...what if a rogue device got on the LAN with 10.10.26.128...what is that? how would you know? so basically you have about 160 devices which leaves a hole of about 64800 available addresses that you have know idea how to manage

 

[burtsbees]

Definitely subnet it to a /24 or /25.

/

tim@tim-laptop ~ $ sudo apt-get install windows
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Couldn't find package windows...Thank Goodness!

 

[pompeychimes]

I definetly agree with the /24 or /25. However, if you really don't want to change masks u can leave them as is and configure your scope to hand out only /24 or /25 addresses. Then i would use security mechanisims like ACL's or firewall rules to prevent any traffic from the /16 minus the allowed /24 or /25

 

[baddos]

Using subnets that closely match their host requirements gives you more flexibility as the company expands as well. It can also help with filtering, etc.

 

[kbing]

The primary concern here is broadcast domain design. Broadcast traffic will increase with the device count. If you have 2000 nodes on a single IP subnet you will have a lot of broadcast traffic and every single NIC will have to process every packet to see if it is for itself or not.

In your case with about 80 or so nodes per subnet that isn't a big deal and is very small network. If you get hundreds of nodes then it'll be a bigger deal.

Wanna know the impact of your network? Install Wireshark and monitor your NIC card and you can see all the misc traffic broadcasting around wasting CPU cycles.

 

[kbing]

I forgot to mention - the point isn't really about the TCPIP subnet size as being the problem...the problem really is the # of live nodes generating traffic.

First I would never subnet a LAN that large - it's unrealistic but it works fine. Second - VLAN's will solve any broadcast domain issues you want to solve - just keep the subnets at /24 and you'll be fine.

 

[pjcarmen]

Thanks kbing, that's just what I was wanting to know.

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"Is it ignorance or apathy? Hey, I don't know and I don't care."
-Jimmy Buffett

 

[robertjo24]

Kbing is correct; a real stinker with such a large subnet is the broadcast traffic. We have a location that is subnetted like this, and the broadcast traffic is very high. If you can avoid it (and you should be able to) I would not have a network configured in this manner. It just opens you up to too many potential problems.

 

[pjcarmen]

Thanks much guys. I have started making changes. One site is complete, and the others are coming along.

Thanks

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"Is it ignorance or apathy? Hey, I don't know and I don't care."
-Jimmy Buffett