In previous artical i discussed about The internetworking problem.For networking we also need IP addresses inspite of networking technology.What is IP address? This is the main concern of this artical.I will discuss something about IP address.
IP addresses:- For any host, computer on a TCP/IP network, a unique id (32 bits in IPv4) written as a collection of 4 decimal numbers (dotted quad) between 0 to 255.
Ex. IP address: 188.8.131.52. Every device must have a unique IP address. All devices pertaining to a common network must reflect a common network portion of address that must be registered with the Internet community provided by some Internet Service Provider (ISP)
IP address class:
Class A: 0 + 7 network ID bits + 24 host ID bits
Class B: 10 + 14 network ID bits + 16 host ID bits
Class C: 110 + 21 network ID bits + 8 host ID bits
Class D: 1110 + 28 multicast address bits
network. local.local.local (for class A IDs)
network.network.network.local (for class C IDs)
IP address of a device MAC address (physical ID)
MAC address is a permanently stamped address. IP address is stored in a configuration file in the local disk.
A single network may be split into a multiple networks for internal use but appear as a single network to outsider. This is the concept of subnets.
Subnet mask:- An address such that when added to network address (in bitwise-and) splits the address into network + subnet + host address.
e.g. IP address: 184.108.40.206 subnet mask 255.254.0.0
Since the leading bit begins with 0, it’s a Class A network with address 220.127.116.11
00001100 00001011 00001010 00001001 IP
+ 11111111 11111110 00000000 00000000 Subnet
00001100 00001010 | 00000000 00000000
Network is extended by 7 more bits. Therefore, this is subnet 10.
The remaining host part is 0.1.10.9 is the host address.
IP and subnet masks are often presented together in this format. e.g. Network address = 18.104.22.168 , subnet mask = 255.255.224.0. In this case, the network address can be written as 22.214.171.124/19
indicating subnet has 19 bits for the network portion of address, and has remaining 13 bits for host part.
Therefore, total number of subnets = -2 = 6
Total numbe of hosts per subnet =
Classless Interdomain Routing (CIDR)
Classfull addresses waste a lot of addresses. Ideally, we could bunch similar network addresses together and reduce ARP table considerably. For a good example, see Tanenbaum
Some distinct networks:
a. 127.0.0.0 is used for loop-back address (typically in the form of 127.0.0.1)
b. When host address is either all 0s (4.2BSD) or all 1s (Unix OS standard), it’s considered a broadcast message.
c. For mobile objects, two addresses: Home address (permanent), and a care-of address. Used only for forwarding IP datagrams and admin functions. Higher layers never use them.
d. Care-of addresses two types: Foreign agent address, and Co-located care of address where mails are sent directly to the device on a foreign net.
TCP/IP includes a protocol suit ARP (Address Resolution Protocol) to map IP addresses to physical addresses by network administrators. The constructed table is called ARP cache.
RARP = Reverse Address resolution Protocol permits the inverse mapping from MAC to corresponding IP address. Hosts such as diskless workstations only knows their MAC addresses when booted but not their IP addresses. This must be obtained from an RARP server source. (RFC 903 for details).
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