Switches, Hubs, and Modems
cancel
Showing results for 
Search instead for 
Did you mean: 

How crucial is subnet mask in this situation?

tschaps
Valued Contributor

How crucial is subnet mask in this situation?

I am trying to help a small school with some network issues. They use a 5304XL as their core switch. Their network range was set up 192.168.0.0/16 giving a subnet mask of 255.255.0.0 (overkill for a school with 150 computers, I know). As far as I could tell on first visit, their DHCP server is distributing only in the range of 192.168.1.10-254, but giving the 255.255.0.0 subnet mask. The core switch has a static IP of 192.168.1.5, but someone set the subnet mask to 255.255.255.0.

As they did a lot of the work themselves, I don't want to go in as a know it all (at least until I check my facts ;), and I don't want to embarrass anyone, but if the scope on the network is set to 192.168.0.0/16 but it only distributes addresses in the range of 192.168.1.0/24, would this core switch set to static IP in that /24 subnet be causing performance problems?
And what if there are actually some devices with IPs outside the /24 range, does the subnet of the switch really matter, or is traffic routed via MAC address?

Thanks in advance.
1 REPLY
Paulen
Regular Advisor

Re: How crucial is subnet mask in this situation?

Hi

It would probably work - however, the client would send ARP requests to find corresponding MAC address on its own subnet (here: /16). Thus, it could never reach something within this /16 that is not within the /24 in question. If the client believes the target is on another subnet, it forwards the request to its default gw (.5).

There should be no problem changing the mask on the DHCP server though.