18.6 Difference between Ethernet and Internet Addresses
|Class||First 4 bits||# Network Bits||# Host Bits||Network Number|
|A||0xxx||7||24||1 to 127|
|B||10xx||14||16||128 to 191|
|C||110x||21||8||192 to 223|
|D||1110||28||Multicast||224 to 239|
These correspond to the following IP addresses characteristics.
|Maximum # of Networks|
The Network and Broadcast addresses are reserved and not used for actual hosts. A Network addresses has a host value of 0, as in 184.108.40.206. A Broadcast address has all ones in the host address, e.g. 220.127.116.11. Earlier versions of SunOS (4.X) use the old style, all zeroes, to indicated the broadcast address, e.g. 18.104.22.168. All Sun systems accepts broadcasts from both the 0 and 255 addresses. If you are running SunOS 4.X you should reset the broadcast in /etc/rc.local to use the 255 address.
An address starting with 127 in the first field designates a loopback address, 127.0.0.1. This refers to the internal interface used by the machine to send a packet to itself. This is usually designated as interface lo0.
On a national basis IP addresses are assigned by the Network Information Center (NIC). Locally, these are assigned by the OSU/UTS NIC. A valid IP address and name would look like:
where 128 --> .edu NIC
.146 --> .ohio-state
and .116.4 --> nyssa.acs UTS
where .116 --> a subnet of .acs.ohio-state.edu
and .4 --> nyssa
IP and hostname pairs are kept in /etc/hosts, which might have the contents:
22.214.171.124 nyssa nyssa.acs.ohio-state.edu loghost
There are 3 class B networks assigned to the Ohio State University:
Which should leave OSU with ample room for expansion for the near future.