Chapter 15. Internet Protocol Principles of Internetworking Connectionless Internetworking Internet Protocol, ICMP IPv6 (IPNG) Multicasting

Internetworking Terms 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

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

Internetworking Protocols

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

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

Internet Protocol Operation

Internet Protocol Operation (cont)

IP Design Issues Routing Datagram lifetime 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

IP Design Issues (cont)

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

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

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

Internet Protocol (cont)

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

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

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

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

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

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

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)

Example of Subnetworking Class C 192.228.17.x Subnet mask 255.255.255.224 Routing table?

ICMP Internet Control Message Protocol ICMP messages 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

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 higher-level 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

ICMP Messages (cont) Time exceeded Parameter problem Source quench 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

ICMP Messages (cont) Redirect Echo and Echo reply 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

ICMP Messages Format

ICMP Messages Format (cont)

IPv6 IP Next Generation (IPng) Motivation IPv6 enhancements The limitation imposed by the 32-bit address field in IPv4 IPv6 enhancements Expanded address space: 128-bit address Improved option mechanism Address autoconfiguration Increased Addressing Flexibility Support for resource allocation Security capabilities

IPv6 Packet

IPv6 Header

IPv6 Header (cont) Traffic class (8 bits) Flow label (20 bits) Available for use by originating nodes and/or forwarding routers to identify and distinguish between different classes or priorities of IPv6 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

IPv6 Header (cont) Payload length (16 bits) Next header (8 bits) Length of the remainder of the IPv6 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)

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, IPv6 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

IPv6 Address Formats

IPv6 Extension Headers Hop-by-Hop Options Header Routing Header Defines special options that require hop-by-hop processing Routing Header Similar to IPv4 source routing Fragment Header Authentication Header Encapsulating Security Payload Header Destination Options Header Contains optional information to be examined by the destination node

IPv6 Extension Headers (cont)

Hop-by-Hop options Options definition Jumbo Payload option 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 IPv6 header Payload length field in IPv6 header must be set to zero, and no fragment header Packet sizes up to more than 4G octets.

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

Fragment Header In IPv6, 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

ICMPv6 4 error messages 3 informational messages Destination unreachable Packet too big Time exceeded Parameter problem 3 informational messages Echo request Echo reply Group membership

ICMPv6 Message Formats

Multicasting broadcast

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

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

IGMP (cont) Message Format Version: Protocol version = 1 Type Checksum 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

IGMP (cont) Group Membership with IPv6 ICMPv6 includes all of the functionality of ICMPv4 and IGMP Multicast support by ICMPv6 Group-membership query message Group-membership report message Group-membership termination message