Network Layer and IP Addressing in Computer Networks, Slides of Computer Networks

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Network Layer

Computer Networks Lect-

NETWORK LAYER

COMPONENTS OF INTERNET’S NETWORK LAYER

»Routing Elements

» Routers , routing protocols

»Internet Protocol

» IPV4 (widely used, classical)

» IPV6 (not very commonly used, new)

»Error Reporting / Control Elements

» ICMP (Internet Control Messaging Protocol)

Computer Networking, DCIS-PIEAS

IP HEADER FORMAT

Computer Networking, DCIS-PIEAS

HEADER FIELDS..CONT..

»Header checksum

» Re-verified and recomputed at each router

» 16 bit ones complement sum of all 16 bit words in header

» Packets with errors are dropped

»Source address and Destination address

» IP address, the same ones which are translated by DNS

»Options

» Dropped in IPv6 as time to process datagram at routers becomes

unpredictable

»Padding

» To fill to multiple of 32 bits long

»Data Filed

» Carries user data from next layer up

» Integer multiple of 8 bits long (octet)

» Max length of datagram (header plus data) 65,535 octets

DATAGRAM FORMAL

» Identification ID (Data unit Identifier)

» 16 bit sequence number

» Sequence number along with source , destination address and protocol

identity uniquely identifies a packet or data unit

» Offset

» A number that specifies that where this fragment should be placed in

actual packet during re-assembly process

» Always multiple of 64 bits, expect the last fragment

» More flag

» Three bit field of which only two are used: more bit , don’t fragment bit

» More bit = 1: there are more fragments of this packet

» More bit = 0: This is the last fragment there is not further fragment

REFRENCES

»IPV TTL

» RFC 1700, J. Reynolds, J. Postel, October 1994

» RFC 1122, R. Braden, Oct 89: extracts from paragraph 3.2.1.

FRAGMENTATION AND RE-ASSEMBLY

IP-ADDRESSING SCHEMES

»Structure of IP Address

»IPv4 Networking Evolution

» Before Classification

» Classfull Networking

» Classless Networking

IP ADDRESS STRUCTURE

»32 bits length

»Doted Decimal Notation

»Each address consist of two parts

» Network Portion

» Host Portion

»Net Mask

» A 32 bit number

» Used to identify network and host portions

» All 1’s represent network number

» All Zero represents host number

» When bitwise And (&&) with IP address generates network number

» Routers use network mask

» Host use network mask for network identification

EXAMPLE..CONT..

Mask^ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0

Address

Bitwise And Operation

Network Number

Host Number

ROUTERS AND NETMASK

R

R

Internet Traffic Internet Traffic

LAN-X

LAN-Y

LAN-Z

IP ADDRESS CLASSES

IP ADDRESSES - CLASS A

»32 bit global internet address

»Network part and host part

»Class A

» Start with binary 0

» All 0 reserved

» 01111111 (127) reserved for loopback

» Range 1.x.x.x to 126.x.x.x

» All allocated