Martin Clarke, 2002-Sep-21 14:33 +0000: > a question i was asked recently on a topic that I thought > i understood untill i was asked.... > > Given the hypothetical subnet 136.206.16.128 and netmask 255.255.255.128, > state the valid range of IP addresses that could be assigned to hosts on > the subnet?(also another was 64.122.34.83 & netmask 255.255.255.240 :( ) > > i was used to looking at plain netmasks ie 255.255.255.0(ffffff00) etc > which I understand fine but my grasp of anything else is less than > good... > > any help is appreciated.. > > thanks > > Martin.
136.206.16.128 255.255.255.128 (/25) network 136.206.16.128 broadcast 136.206.16.255 hosts 136.206.16.129-254 * 64.122.34.83 is actually a host in the 64.122.34.80/28 network: 64.122.34.80 255.255.255.240 (/28) network 64.122.34.80 broadcast 64.122.34.95 hosts 64.122.34.81-94 When you start working with netmasks where octets are something other than a 0 or a 255, you're breaking the classful networks into smaller subnets. The 255.255.255.128 mask breaks a class C network into 2 networks. Each time you break up a classful network, you burn 2 addresses in each subnet, 1 for the new network and 1 for the new broadcast. I common practice in large routed networks is to use a /30 subnet mask, 255.255.255.252, which gives you a network address, a broadcast address and 2 host addresses which are used for the two endpoints of the routed link. This conserves the host addresses that would never be used on the routed link. I used to do these calculations by hand, until I found gipsc, which is an IP calculator. I suggest installed gipsc and playing around with it. You start to see how the classful networks changes when you break into them. Start with a Class C network, go the the CIDR tab and play with the Subnet Bits. You'll see the long form of the mask change. Then go to the Subnets/Hosts tab and see the ranges. The ranges shows the network and broadcast addresses and everything in between are for hosts. I hope this helps, jc -- Jeff Coppock Systems Engineer Diggin' Debian Admin and User -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
