Telecommunications Networking IIThe IP (layer 3) Internet ProtocolIPIP HeaderIP Header ContentsSlide 6Slide 7IP Addresses (IPv4)Looking Up an IP AddressThe Address Resolution Protocol ARPCopyright 1999, S.D. Personick. All Rights Reserved.Telecommunications Networking IILecture 30The Internet(working) Protocol (IP)Tanenbaum: pp 412-424Copyright 1999, S.D. Personick. All Rights Reserved.The IP (layer 3) Internet Protocol•The purpose of the IP layer protocol is to accept datagrams from the Transport protocol (layer 4) and to deliver them to their designated address on a “best effort” basis•Issues we will be concerned with here are-the IP header format-the IP address structure and how it is interpretedCopyright 1999, S.D. Personick. All Rights Reserved.IPTransportLayer PacketIPHeader•IP DatagramIP datagram = Transport Layer Packet + IP Header20 bytes + optional fieldRouterCopyright 1999, S.D. Personick. All Rights Reserved.IP Header Version IHL Type of Service Total Length32 bitsIdentification DM Fragment OffsetTime to Live Protocol Header ChecksumSource AddressDestination AddressOptions (0 or more 32-bit words)Copyright 1999, S.D. Personick. All Rights Reserved.IP Header Contents•Version: which version of the IP protocol (4 bits)•IHL: Header length: in 32 bit words (4 bits)•Type of Service: Precedence (3 bits); Delay, Throughput, Reliability (3 bits)Type of service is currently ignored by most routers, but will become increasingly important in the futureCopyright 1999, S.D. Personick. All Rights Reserved.IP Header Contents•Total length: Specifies the total length of the IP packet, up to 65,535 bytes (16 bits)•Frag m entation:-Identification: identifies the datagram that a fragment belongs to (16 bits)-DF: don’t fragment (1 bit)-MF: more fragments (1 bit)-Fragment offset: (13 bits)Copyright 1999, S.D. Personick. All Rights Reserved.IP Header Contents•Time to Live: Essentially a hop counter that is decremented from 255 down to zero as a datagram goes through a sequence of N routers (8 bits)•Protocol: Defines the transport layer protocol that the IP datagram should be delivered to (e.g., TCP, UDP) (8 bits)•Header Checksum: (16 bits)Copyright 1999, S.D. Personick. All Rights Reserved.IP Addresses (IPv4)129 25 60 1SDP’s mail serverNetwork address: 1,2 or 3 bytes (0,10, 110)Host address: 1,2, or 3 bytes Host + Network = 4 bytesAssigned by the Network Information Center (NIC) DrexelCopyright 1999, S.D. Personick. All Rights Reserved.Looking Up an IP AddressDrexel GatewayRouter129.25.60.1144.118.0.0Everything elseRouting Table129.25.0.0129.25.60.1Copyright 1999, S.D. Personick. All Rights Reserved.The Address Resolution ProtocolARPLayer 4IP Datagram (129.25.60.1)Layer 3Ethernet Frame (E2)Layer 3129.25.60.1IP Datagram2Layer
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