Chapter 15 Internet Protocol Principles of Internetworking Connectionless

Chapter 15. Internet Protocol • Principles of Internetworking • Connectionless Internetworking • Internet Protocol, ICMP • IPv 6 (IPNG) • Multicasting 1

Internetworking Terms • Internet – A collection of communications networks interconnected by bridges and/or routers • Subnetwork – Refers to a constituent network of an internet • End system (ES) – A device attached to one of the subnetworks of an internet that is used to support end-user applications or services 2

Internetworking Terms (cont) • Intermediate System (IS) – A device used to connect two subnetworks and permit communication between end systems attached to different subnetworks • Bridge – An IS used to connect two LANs that use identical LAN protocols – Operates an layer 2 of the OSI model • Router – An IS used to connect two networks that may or may not be similar – Operates at layer 3 of the OSI model 3

Internetworking Protocols 4

Internetworking Mode • Connection-mode operation Virtual circuit is set up across each subnet DTE A Each IS splices together two virtual circuits IS I Subnet 1 Subnet 2 IS M Subnet 4 IS K IS J Subnet 3 DTE B IS L 5

Internetworking Mode (cont) • Connectionless-mode operation DTE A makes a separate routing decision for each PDU, choosing either IS I or J DTE A For each incoming PDU, the IS makes a separate routing decision Subnet 2 IS M IS I Subnet 1 Subnet 4 IS K IS J Subnet 3 DTE B IS L 6

Internet Protocol Operation 7

Internet Protocol Operation (cont) 8

IP Design Issues • Routing – static/dynamic routing table • Datagram lifetime – Using hop count • Fragmentation and Reassembly – In IP, datagram fragments are reassembled at the destination end system – Fields used by the IP segmentation techniques • Data Unit Identifier (ID): source and destination address, an identifier of the protocol layer, a sequence number supplied by that protocol layer • Data Length, Offset, More-flag 9

IP Design Issues (cont) 10

Internet Protocol • IP Services Send ( Deliver ( Source address Destination address IP user Protocol Type of service indicators Identifier Don’t-fragment identifier Time to live Data length Option data Data ) ) 11

Internet Protocol (cont) • IP service quality options – Precedence: 8 levels – Reliability: 2 levels (normal or high) – Delay: 2 levels (normal or high) – Throughput: 2 levels (normal or high) • Currently defined options – Security • Allows a security label to be attached to a datagram 12

Internet Protocol (cont) – Source routing • A sequenced list of router addresses that specifies the route to be followed – Route Recording • A field is allocated to record the sequence of routers visited by the datagram – Stream identification • Names reserved resources used for stream services – Timestamping • The source IP entity and some or all intermediate routes add a timestamp to the data unit as it goes by 13

Internet Protocol (cont) 14

IP Header Fields • Internet header length (IHL) (4 bits) – Length of header in 32 -bit words – Minimum value is five, for a min. header length of 20 octets • Type of service (8 bits) – Specifies precedence, reliability, delay and throughput parameters • Total length (16 bits) – Total datagram length, in octets 15

IP Header Fields (cont) • Identification (16 bits) – A sequence number that, together with the source address, destination address, and user protocol, is intended to identify a datagram uniquely • Flags (3 bits) – Only two bits are currently defined – More bit: for fragmentation and reassembly – Don’t Fragment bit: prohibits fragmentation 16

IP Header Fields (cont) • Fragment offset (13 bits) – Indicates where in the original datagram this fragment belongs, measured in 64 -bit unit • Time to live (8 bits) – Specifies how long, in seconds, a datagram is allowed to remain in the internet – Every router that processes a datagram must decrease the TTL by at least one, so the TTL is somewhat similar to a hop count 17

IP Header Fields (cont) • Protocol (8 bits) – Indicates the next higher protocol that is to receive the data field at the destination • Header checksum (16 bits) – This is re-verified and recomputed at each router • Option (variable) • Padding (variable) – Used to ensure that the datagram header is a multiple of 32 bits in length 18

IP Addresses 1 ~ 126. . . 128 ~ 191. . . 192 ~ 223. . . 224 ~. . . 19

Subnets, Subnet Masks • host portion of the internet address is partitioned into a subnet number and a host number 20

Subnets, Subnet Masks (cont) • Address mask: allows the host to determine whether an outgoing datagram is destined for a host on the same LAN (send directly) or another LAN (send datagram to router) 21

Example of Subnetworking Class C 192. 228. 17. x Subnet mask 255. 224 Routing table? 22

ICMP • Internet Control Message Protocol – Provides feedback about problems in the communication environment • ICMP messages – – – – Destination unreachable Time exceeded Parameter problem Source quench Redirect Echo, Echo reply Timestamp, Timestamp reply Address mask request/reply 23

ICMP Messages • Destination unreachable – A router may return this message if it does not know how to reach the destination network – A particular host is unreachable – The destination host itself may return this message if the user protocol or some higherlevel service access point is unreachable – The datagram specifies a source route that is unusable – If a router must fragment a datagram but the Don’t-Fragment flag is set 24

ICMP Messages (cont) • Time exceeded – A router will return this message if the lifetime of the datagram expires – A host will send this message if it cannot complete reassembly within a time limit • Parameter problem – A syntactic or semantic error in an IP header • Source quench – This message can be used by a router or host that must discard datagrams because of a full buffer 25

ICMP Messages (cont) • Redirect – A router sends this message to a host on a directly connected router to advise the host of a better route to a particular destination • Echo and Echo reply – Provide a mechanism for testing that communication is possible between entities • Timestamp and Timestamp reply – Provide a mechanism for sampling the delay characteristics of the internet • Address mask request/reply – Useful for subnets 26

ICMP Messages Format 27

ICMP Messages Format (cont) 28

IPv 6 • IP Next Generation (IPng) • Motivation – The limitation imposed by the 32 -bit address field in IPv 4 • IPv 6 enhancements – – – Expanded address space: 128 -bit address Improved option mechanism Address autoconfiguration Increased Addressing Flexibility Support for resource allocation Security capabilities 29

IPv 6 Packet 30

IPv 6 Header 31

IPv 6 Header (cont) • Traffic class (8 bits) – Available for use by originating nodes and/or forwarding routers to identify and distinguish between different classes or priorities of IPv 6 packets – Still under study • Flow label (20 bits) – May be used by a host to label those packets for which it is requesting special handling by routers 32

IPv 6 Header (cont) • Payload length (16 bits) – Length of the remainder of the IPv 6 packet following the header, in octets. – That is, total length of all of the extension headers plus the transport-level PDU • Next header (8 bits) • Hop limit (8 bits) 33

Flow Label • A flow is uniquely identified by the combination of a source address, destination address, and a nonzero 20 -bit flow label • Thus, all packets that are to be part of the same flow are assigned the same flow label by the source • In principle, all of a user’s requirements for a particular flow could be defined in an extension header and included with each packet • Alternatively, IPv 6 could make use of the flow requirements for the flow with a unique flow label. In this case, the router must save flow requirement about each flow 34

IPv 6 Address Formats 35

IPv 6 Extension Headers • Hop-by-Hop Options Header – Defines special options that require hop-by-hop processing • Routing Header – Similar to IPv 4 source routing • Fragment Header • Authentication Header • Encapsulating Security Payload Header • Destination Options Header – Contains optional information to be examined by the destination node 36

IPv 6 Extension Headers (cont) 37

Hop-by-Hop options • Options definition – Option type (8 bits), Length (8 bits), Option Data (variable) • Jumbo Payload option – Option data field is 32 bits long and gives the length of the packets in octets, excluding the IPv 6 header – Payload length field in IPv 6 header must be set to zero, and no fragment header – Packet sizes up to more than 4 G octets. 38

Hop-by-Hop options (cont) • Router Alert option – Informs the router that the contents of the packet is of interest to the router – The purpose of this option is to provide efficient support for protocols such as RSVP that generate packets that need to be examined by intermediate routers for purpose of traffic control 39

Fragment Header • In IPv 6, fragmentation may only be performed by source nodes, not by routers along the path • A node must perform a path discovery algorithm that enables it to learn the smallest MTU supported by any network on the path • Otherwise, limit all packets to 1280 octets 40

ICMPv 6 • 4 error messages – Destination unreachable – Packet too big – Time exceeded – Parameter problem • 3 informational messages – Echo request – Echo reply – Group membership 41

ICMPv 6 Message Formats 42

Multicasting broadcast 43

Multicasting (cont) Broadcast a copy of each pkt to each network in the configuration 44

IGMP • Internet Group Management Protocol – Defined in RFC 1112 – Used by the hosts and routers to exchange multicast group membership information over a LAN 45

IGMP (cont) • Message Format – Version: Protocol version = 1 – Type • Type 1: query sent by a multicast router • Type 0: report sent by a host – Checksum – Group Address • Zero in a request message • Valid group address in a report message 46

IGMP (cont) • Group Membership with IPv 6 – ICMPv 6 includes all of the functionality of ICMPv 4 and IGMP – Multicast support by ICMPv 6 • Group-membership query message • Group-membership report message • Group-membership termination message 47