Internet Technologies IP Addressing

Transcription

1 QAFQAZ UNIVERSITY Computer Engineering Department Internet Technologies IP Addressing Dr. Abzetdin ADAMOV Chair of Computer Engineering Department

2 IP Addressing Primary job of IP delivering messages IP Addressing Network Interface Identification Routing Become more complicated with subnetting and classless addressing Rest of the class IP addressing schemes

3 Dotted decimal notation Example: We can view these values in their binary form. 32 bit binary Four 8-bit octets Ex: E D - B1 What s a subnet? device interfaces with same subnet part of IP address can physically reach each other without intervening router

4 Internet IP Address Structure 32 bits have an internal structure with 2 components Network Identifier (Network ID) Host Identifier (Host ID) Like a telephone number! (401) The fundamental division of the bits of an IP address is into a network ID and host ID. Here, the network ID is 8 bits long, shown in cyan, and the host ID is 24 bits in length.

5 Why we needed IP address classes? It became clear that a low number of independent networks would not be enough; We or network devices need to be able to observe IP address and determine the network and host parts; To avoid delivering off packages to extremely many (2 24 ) hosts of each (2 8 ) network, even if it is not necessary.

6 IP classifying history RFC 760 from 1980 one octet for network RFC 791 from 1981 multi classes RFC 950 Internet Standard Subnetting Procedure from 1985

7 IP Address Scheme Categories Conventional ( Classful ) Addressing Dividing line occurs only at octet boundaries A, B, and C depending on how many octets for network ID and host ID Subnetted Classful Addressing 3 tier system: network ID, subnet ID, host ID Ex: Class C 24 (NID) + 8 (HID) 24(NID) + 3(SID) + 5 (HID)

8 Classful Addressing IP Addre ss Class Class A Class B Class C Class D Class E Fraction of Total IP Address Space Number Of Network ID Bits Number Of Host ID Bits 1/ / / Intended Use Unicast addressing for very large organizations with hundreds of thousands or millions of hosts to connect to the Internet. Unicast addressing for medium-to-large organizations with many hundreds to thousands of hosts to connect to the Internet. Unicast addressing for smaller organizations with no more than about 250 hosts to connect to the Internet. 1/16 n/a n/a IP multicasting. 1/16 n/a n/a Reserved for experimental use.

9 "Classful" Addressing Class Determination Algorithm If the first bit is a 0, it's a class A address and we're done. (Half the address space has a 0 for the first bit, so this is why class A takes up half the address space.) If it's a 1, continue to step two. If the second bit is a 0, it's a class B address and we're done. (Half of the remaining non-class-a addresses, or one quarter of the total.) If it's a 1, continue to step three. If the third bit is a 0, it's a class C address and we're done. (Half again of what's left, or one eighth of the total.) If it's a 1, continue to step four. If the fourth bit is a 0, it's a class D address. (Half the remainder, or one sixteenth of the address space.) If it's a 1, it's a class E address. (The other half, one sixteenth.)

10 Class based IP Addressing Class First octet range Leading bits Size of networ k bit field Size of rest bit field Number of networks A * (2 7 ) B C D E not defined not defined not defined not defined 16,384 (2 14 ) 2,097,152 (2 21 ) not defined not defined Addresses per network 16,777,216 (2 24 ) 65,536 (2 16 ) 256 (2 8 ) not defined not defined Note: Addresses to cannot be used in addressing and are reserved for loopback (try to ping ).

11 IP range and Bit-wise representation of classes Classes IP range Bit-wise representation A nnnnnnn.hhhhhhhh.hhhhhhhh.hhhhhhhh B C D E n - specifies the bits used to determine network ID; h - specifies the bits used to determine host ID; x - specifies the bits without certain purpose nnnnnn.nnnnnnnn.hhhhhhhh.hhhhhhhh nnnnn.nnnnnnnn.nnnnnnnn.hhhhhhhh xxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx xxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx

12 Summary of Classful Addressing Issues Lack of Internal Address Flexibility Big organizations are assigned large, monolithic blocks of addresses that don't match well the structure of their underlying internal networks. Inefficient Use of Address Space The existence of only three block sizes (classes A, B and C) leads to waste of limited IP address space. Proliferation of Router Table Entries As the Internet grows, more and more entries are required for routers to handle the routing of IP datagrams, which causes performance problems for routers. Attempting to reduce inefficient address space allocation leads to even more router table entries.

13 Subnetting Concepts Revise: binary nos., boolean operators AND Phone number analogy still works! (401) Host ID: divided into Subnet ID and Host ID Need to communicate which part is subnet ID 32 bit binary number called Subnet mask The bits of the mask in any given subnetted network are chosen so that the bits used for either the network ID or subnet ID are ones, while the bits used for the host ID are zeroes.

14 Why we need IP address subnetting? To prevent wasteful use of IP addresses by making possible to allocate the number of addresses much closer to the required number. Increase security by dividing the network to segments and minimizing the number of nodes can see transmitted packets. Increase network performance though elimination the number of collisions.

15 Subnetting Concepts (Cont) Subnet Bit Is A One: In this case, we are ANDing either a 0 or 1 in the IP address with a 1. If the IP address bit is a 0, the result of the AND will be 0, and if it is a 1, the AND will be 1. In other words, where the subnet bit is a 1, the IP address is preserved unchanged. Subnet Bit Is A Zero: Here, we are ANDing with a 0, so the result is always 0 regardless of what the IP address is. Thus, when the subnet bit is a 0, the IP address bit is always cleared to 0. A router that performs this function is left with the address of the subnet. Since it knows from the class of the network what part is the network ID, it also knows what subnet the address is on. Bit Allocation Example We can decide to use 1 bit for the subnet ID and 15 bits for the host ID. If we do this, then the total number of subnets is 2 1 or 2: the first subnet is 0 and the second is 1. The number of hosts available for each subnet is or 32,766.

16 Subnetting Concepts (Cont) Creating subnets through dividing host identifier Network Number Host Number Network Number Subnet Number Host Number Presenting a Class C Subnetting as Three-Level Addressing Hierarchy Byte 1 Byte 2 Byte 3 Byte XXXX XXXXXXXX XXXXXXXX 1111XXXX Network Host Subnet Extended Network Host

17 Subnetting Example sub ---- extended mask: subnetting bits Subnet Address Extended Mask Host Address Range

18 Subnetting Task sub ---- subnetting bits

19 Example: IP Subnetting Requirements Class, how many hosts, scalability, min, max Subnetting Design Trade-Off For Class C Networks

20 Class C Custom Subnet Mask Calculation Example 3 for subnet ID and 5 for host ID Express Subnet Mask In Slash Notation : is equivalent to /27.

21 Determining Host Address for each Subnet

22 CIDR Notation According to this standard: 1. Network with standard network mask can be written as /16 2. Network with extended network mask can be written as /22 (it means that network portion of this address consist of 22 first bits) CIDR and was introduced in 2006 (RFC 4632). Classes IP range Subnet Mask CIDR Notation A / B / C / D E

23 Classful routing Internet Network IP Address Extended Network Mask Subnet Mask / / /224 Internet routing used to work like this: 1. A router receiving an IP packet extracted its Destination IP Address 2. Determined address's class by examining its first one to four bits 3. Ignored the host bits, and only needed the network bits to find a route to the network 4. Once a packet reached its target network, its host field was examined for final delivery. Subnets and Addresses 000 / / / / / / / /

24 References TCP/IP guides: g123.shtml