Hi, First, an overview on "Netmask". Every IP address has 2 parts. A "network" park and a "host" part. So the total 32 bits of IP address are broken into "network" bits and "host" bits. The NETMASK (network mask) parameter decides how many bits belong to the network part, and how many to host part. The "1" bits in the netmask tell that the corresponding bits in ANY IP address are to be treated as "network" bits, the rest as host bits. Every computer in a LAN / subnet HAS to have the same "network" part. The host part may differ. For eg, if you decide to devote 16 bits to network part, and you give the computer an IP address 122.122.122.122, then left most 16 bits are network part. And hence the network address is "122.122.0.0" (A network address has all host bits set to 0). This represents the address of the NETWORK (subnet) as a whole (meaning THIS network, instead of any particular PC). Similarly, every network has a "Broadcast Address". If a computer sends a packet addressed to the "broadcast address" of a network, then it will be delievered to all the computers on the network. A broad cast address has all the host bits set to 1. Hence for the above case, the broad cast address of the network will be 122.122.255.255. The "Network Address" and "Broadcast addres" are reserved and you cannot assign them to any computer in your network.. Your Case ============ I might be totally wrong, but here is my understanding. You set the IP address 122.122.122.122. But setting the netmask to 255.255.255.255 is WRONG. This means there are all network bits and no host bits. So essentially you are having a single host network (since no host bits). Regards, Rajat -----Original Message----- From: linux-net-owner@xxxxxxxxxxxxxxx [mailto:linux-net-owner@xxxxxxxxxxxxxxx] On Behalf Of david.balazic@xxxxxxxxx Sent: Monday, January 31, 2005 6:47 PM To: linux-net@xxxxxxxxxxxxxxx Subject: Exact meaning of netmask for ifconfig ? Hi! As I am configoring a rather unusual network setup, I must know the exact meaning of the NETMASK (and BROADCAST) paramaters of the ifconfig command. Currently I use : ifconfig eth0 122.122.122.122 netmask 255.255.255.255 (IP not real ) "ifconfig eth0" then prints, that eth0 has a broadcast address of 122.255.255.255, which does not look right. Later I set this routing : route add 10.49.1.1 dev eth0 route add default gw 10.49.1.1 Will this work ? I am currently testing under knoppix 3.7 on a single PC, not in the real target network. Background or "Why am I doing this" ? A PC will be conncted to an ADSL modem. It will have a PPPoE session to the ISP. Two other PCs will be connected to the first PC. The ISP assigned two static IP adresses, that I want to set for the two PCs ( not the "router" PC ). Regards, David Bala.ic - : send the line "unsubscribe linux-net" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html - : send the line "unsubscribe linux-net" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
