On Tue, Jul 08, 2003 at 08:39:55AM +0300, Oron Peled wrote: > > So for your case you need two bits -- i.e: 255.255.255.252 > Now calculate the 2 correct host numbers as an exercise (and > reply to the group, so others will benefit as well...) >
A possible allocation of IPs with a 255.255.255.252 netmask might be: network address: 192.168.0.8. 1st host: 192.168.0.9. 2nd host: 192.168.0.10. broadcast address: 192.168.0.11. Another similar example: network address: 192.168.25.252. 1st host: 192.168.25.253. 2nd host: 192.168.25.254. broadcast address: 192.168.25.255. I still don't get something. Quoting section 7 of the IP Sub-Networking Mini-Howto: \bgein{quotation} For the sake of this example, let us assume that you have decided to subnetwork you C class IP network number 192.168.1.0 into 4 subnets (each of 62 usable interface/host IP numbers). However, two of these subnets are being combined into a larger single network, giving three physical networks. These are :- ______________________________________________________________________ Network Broadcast Netmask Hosts 192.168.1.0 192.168.1.63 255.255.255.192 62 192.168.1.64 192.168.1.127 255.255.255.192 62 192.168.1.128 192.168.1.255 255.255.255.128 124 (see note) ______________________________________________________________________ Note: the reason the last network has only 124 usable network addresses (not 126 as would be expected from the network mask) is that it is really a 'super net' of two subnetworks. Hosts on the other two networks will interpret 192.168.1.192 as the network address of the 'non-existent' subnetwork. Similarly, they will interpret 192.168.1.191 as the broadcast address of the 'non-existent' subnetwork. So, if you use 192.168.1.191 or 192 as host addresses on the third network, then machines on the two smaller networks will not be able to communicate with them. \begin{interruptRequest} How does the 2 smaller networks know that 192.168.1.191 and 192 were initially a broadcast and network addresses? Would they treat any one of 192.168.*.19[12] in the same way? \end{interruptRequest} This illustrates an important point with subnetworks - the usable addresses are determined by the SMALLEST subnetwork in that address space. 7.1. The routing tables Let us assume that a computer running Linux is acting as a router for this network. It will have three network interfaces to the local LANs and possibly a fourth interface to the Internet (which would be its default route. Let us assume that the Linux computer uses the lowest available IP address in each subnetwork on its interface to that network. It would configure its network interfaces as ______________________________________________________________________ Interface IP Address Netmask eth0 192.168.1.1 255.255.255.192 eth1 192.168.1.65 255.255.255.192 eth2 192.168.1.129 255.255.255.128 ______________________________________________________________________ The routing it would establish would be ______________________________________________________________________ Destination Gateway Genmask Iface 192.168.1.0 0.0.0.0 255.255.255.192 eth0 192.168.1.64 0.0.0.0 255.255.255.192 eth1 192.168.1.128 0.0.0.0 255.255.255.128 eth2 ______________________________________________________________________ On each of the subnetworks, the hosts would be configured with their own IP number and net mask (appropriate for the particular network). Each host would declare the Linux PC as its gateway/router, specifying the Linux PCs IP address for its interface on to that particular network. Robert Hart Melbourne, Australia March 1997. \end{quotation} I will repeat the question in case you haven't noticed that I have \begin{interruptRequest} in the middle: How does the 2 smaller networks know that 192.168.1.191 and 192 were initially a broadcast and network addresses? Would they treat any one of 192.168.*.19[12] in the same way? -- Shaul Karl, [EMAIL PROTECTED] e t ================================================================= To unsubscribe, send mail to [EMAIL PROTECTED] with the word "unsubscribe" in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]