CCNA - Company IP addresses, CCNA confused!!!

Author

Company IP addresses, CCNA confused!!!

Spides

2003-02-11, 4:53 pm

I’m at a company who are using a 192.168 range of IP addresses. There subnet mask is 255.255.255.0. Now I thought this was a default class C addressing system. So how are they having addresses of 192.168.10.3 or 192.168.20.15 my point is that the third octet has changed. I thought this could only be done on a class B addressing. Perhaps I need to swot up on my subnetting, it’s been a while.

larkspur

2003-02-11, 9:05 pm

Are they using DHCP? If so then I believe supernetting might be involed.

Spides

2003-02-11, 9:23 pm

Nope no DHCP servers on the network. All IP's are static and are assigned when a new machine is installed by a technician. Anyone else know. I don't want to ask the Administrators, I'm more qualified than them. Not that it counts for anything!!!

edmonds_robert

2003-02-11, 10:04 pm

Spides,
You're misunderstanding something somewhere. They are able to do this because each subnet uses the subnet mask 255.255.255.0. What the subnet mask tells the device is, if it wants to go from the subnet 192.168.10.0 to the subnet 192.168.20.0 then it is going to have to go through a router, aka default gateway, to get there.
The subnet mask and class of an IP address do not dictate what can change and what can't. As a matter of fact, with more and more classless routing protocols (EIGRP, RIPv2, etc.) in use and CIDR, even address class doesn't mean all that much any more.
The subnet mask really just tells how many computers are on the network. In your example, with the subnet mask of 255.255.255.0, each network contains 254 useable addresses. That means there can be 254 devices on the network 192.168.10.0 and 254 more on the network 192.168.20.0.
Check out the following links for a little more help:

http://www.cisco.com/en/US/customer... 800a67f5.shtml

http://www.learntosubnet.com/

Hope that helps a little.

Spides

2003-02-11, 11:02 pm

Good explanation, thanks.

Sponsored Links