Chapter 15 Internetwork Protocols

William Stallings

Data and Computer

Communications

Chapter 15

Internetworking Terms (1)

 _{Communications Network}

 _{Facility that provides data transfer service}

 _{An internet}

 _{Collection of communications networks interconnected}

by bridges and/or routers

 _{The Internet - note upper case I}

 _{The global collection of thousands of individual}

machines and networks

 _Intranet

 _{Corporate internet operating within the organization}  _{Uses Internet (TCP/IP and http)technology to deliver}

Internetworking Terms (2)

 _{End System (ES)}

 _{Device attached to one of the networks of an} internet

 _{Supports end-user applications or services}  _{Intermediate System (IS)}

 _{Device used to connect two networks}

Internetworking Terms (3)

 _Bridge

 _{IS used to connect two LANs using similar}

LAN protocols

 Address filter passing on packets to the

required network only

 _{OSI layer 2 (Data Link)}

 _Router

 _{Connects two (possibly dissimilar) networks}

 _{Uses internet protocol present in each}

router and end system

Requirements of Internetworking

 _{Link between networks}

 _{Minimum physical and link layer}

 _{Routing and delivery of data between}

processes on different networks

Network Architecture Features

 _Addressing  _{Packet size}

 _{Access mechanism}  _Timeouts

 _{Error recovery}  _{Status reporting}  _Routing

 _{User access control}

Architectural Approaches

Connection Oriented

 _{Assume that each network is connection}

oriented

 _{IS connect two or more networks}

 _{IS appear as DTE to each network}

 _{Logical connection set up between DTEs}  _{Concatenation of logical connections}

across networks

 _{Individual network virtual circuits joined by IS}  _{May require enhancement of local network}

services

Connection Oriented IS Functions

 _Relaying  _Routing

 _{e.g. X.75 used to interconnect X.25 packet}

switched networks

Connectionless Operation

 _{Corresponds to datagram mechanism in}

packet switched network

 _{Each NPDU treated separately}

 _{Network layer protocol common to all DTEs}

and routers

 _{Known generically as the internet protocol}

 _{Internet Protocol}

 _{One such internet protocol developed for}

ARPANET

 _{RFC 791 (Get it and study it)}

 _{Lower layer protocol needed to access}

Connectionless Internetworking

 _Advantages  _Flexibility  _Robust

 _{No unnecessary overhead}  _Unreliable

 _{Not guaranteed delivery}

 _{Not guaranteed order of delivery}  _{Packets can take different routes}

 _{Reliability is responsibility of next layer}

Design Issues

 _Routing

 _{Datagram lifetime}

 _{Fragmentation and re-assembly}  _{Error control}

Routing

 _{End systems and routers maintain routing tables}

 _{Indicate next router to which datagram should be sent}  _Static

 _{May contain alternative routes}  _Dynamic

 _{Flexible response to congestion and errors}

 _{Source routing}

 _{Source specifies route as sequential list of routers to}

be followed

 _Security  _Priority

Datagram Lifetime

 _{Datagrams could loop indefinitely}

 _{Consumes resources}

 _{Transport protocol may need upper bound on}

datagram life

 _{Datagram marked with lifetime}

 _{Time To Live field in IP}

 _{Once lifetime expires, datagram discarded (not}

forwarded)

 _{Hop count}

 _{Decrement time to live on passing through a each}

router

 _{Time count}

 _{Need to know how long since last router}

Fragmentation and

Re-assembly

 _{Different packet sizes}  _{When to re-assemble}

 _{At destination}

 _{Results in packets getting smaller as}

data traverses internet

 _{Intermediate re-assembly}

 _{Need large buffers at routers}  _{Buffers may fill with fragments}

 _{All fragments must go through same}

router

IP Fragmentation (1)

 _{IP re-assembles at destination only}  _{Uses fields in header}

 _{Data Unit Identifier (ID)}

 _{Identifies end system originated}

datagram

•_{Source and destination address}

•_{Protocol layer generating data (e.g.} TCP)

•_{Identification supplied by that layer}

 _{Data length}

IP Fragmentation (2)

 _Offset

 _{Position of fragment of user data in}

original datagram

 _{In multiples of 64 bits (8 octets)}  _{More flag}

 _{Indicates that this is not the last}

Dealing with Failure

 _{Re-assembly may fail if some fragments}

get lost

 _{Need to detect failure}  _{Re-assembly time out}

 _{Assigned to first fragment to arrive}

 _{If timeout expires before all fragments}

arrive, discard partial data

 _{Use packet lifetime (time to live in IP)}

Error Control

 _{Not guaranteed delivery}

 _{Router should attempt to inform source if}

packet discarded

 _{e.g. for time to live expiring}

 _{Source may modify transmission strategy}  _{May inform high layer protocol}

Flow Control

 _{Allows routers and/or stations to limit rate}

of incoming data

 _{Limited in connectionless systems}  _{Send flow control packets}

Internet Protocol (IP)

 _{Part of TCP/IP}

 _{Used by the Internet}

 _{Specifies interface with higher layer}  _{e.g. TCP}

IP Services

 Primitives

 _{Functions to be performed}

 _{Form of primitive implementation}

dependent

 _{e.g. subroutine call}

 _Send

 _{Request transmission of data unit}

 _Deliver

 _{Notify user of arrival of data unit}

 _Parameters

Parameters (1)

 _{Source address}

 _{Destination address}  _Protocol

 _{Recipient e.g. TCP}  _{Type of Service}

 _{Specify treatment of data unit during} transmission through networks

 _{Identification}

 _{Source, destination address and user protocol}  _{Uniquely identifies PDU}

Parameters (2)

 _{Don’t fragment indicator}  _{Can IP fragment data}

 _{If not, may not be possible to deliver}  _{Send only}

Type of Service

 _Precedence  _{8 levels}  _Reliability

 _{Normal or high}  _Delay

 _{Normal or low}  _Throughput

Options

 _Security

 _{Source routing}  _{Route recording}

Header Fields (1)

 _Version

 _{Currently 4}

 _{IP v6 - see later}

 _{Internet header length}  _{In 32 bit words}

 _{Including options}  _{Type of service}

 _{Total length}

Header Fields (2)

 _{Identification}

 _{Sequence number}

 _{Used with addresses and user protocol to identify}

datagram uniquely

 Flags

 _{More bit}

 _{Don’t fragment}

 _{Fragmentation offset}

 _{Time to live}

 _Protocol

 _{Next higher layer to receive data field at}

Header Fields (3)

 _{Header checksum}

 _{Reverified and recomputed at each}

router

 16 bit ones complement sum of all 16

bit words in header

 _{Set to zero during calculation}

 _{Source address}

 _{Destination address}

 _Options

 _Padding

Data Field

 _{Carries user data from next layer up}  _{Integer multiple of 8 bits long (octet)}  _{Max length of datagram (header plus}

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}

IP Addresses - Class B

 _{Start 10}

 _{Range 128.x.x.x to 191.x.x.x}

 _{Second Octet also included in network}

address

IP Addresses - Class C

 _{Start 110}

 _{Range 192.x.x.x to 223.x.x.x}

 _{Second and third octet also part of}

network address

 ₂21 = 2,097,152 addresses  _{Nearly all allocated}

Subnets and Subnet Masks

 _{Allow arbitrary complexity of internetworked} LANs within organization

 _{Insulate overall internet from growth of network} numbers and routing complexity

 _{Site looks to rest of internet like single network}  _{Each LAN assigned subnet number}

 _{Host portion of address partitioned into subnet} number and host number

 _{Local routers route within subnetted network}  _{Subnet mask indicates which bits are subnet}

ICMP

 _{Internet Control Message Protocol}  _{RFC 792 (get it and study it)}

 _{Transfer of (control) messages from}

routers and hosts to hosts

 _{Feedback about problems}  _{e.g. time to live expired}

IP v6 - Version Number

 _{IP v 1-3 defined and replaced}  _{IP v4 - current version}

 _{IP v5 - streams protocol}

 _{IP v6 - replacement for IP v4}

Why Change IP?

 _{Address space exhaustion}

 _{Two level addressing (network and host)}

wastes space

 _{Network addresses used even if not}

connected to Internet

 _{Growth of networks and the Internet}  _{Extended use of TCP/IP}

 _{Single address per host}

IPv6 RFCs

 _{1752 - Recommendations for the IP Next}

Generation Protocol

 _{Expanded address space}  _{128 bit}

 _{Improved option mechanism}

 _{Separate optional headers between IPv6}

header and transport layer header

 _{Most are not examined by intermediate}

routes

 _{Improved speed and simplified router}

processing

 _{Easier to extend options}  _{Address autoconfiguration}

IPv6 Enhancements (2)

 _{Increased addressing flexibility}

 _{Anycast - delivered to one of a set of}

nodes

 _{Improved scalability of multicast}

addresses

 _{Support for resource allocation}  _{Replaces type of service}

 _{Labeling of packets to particular traffic}

flow

Extension Headers

 _{Hop-by-Hop Options}

 _{Require processing at each router}  _Routing

 _{Similar to v4 source routing}  _Fragment

 _{Authentication}

 _{Encapsulating security payload}  _{Destination options}

IP v6 Header Fields (1)

 _Version  ₆

 _{Traffic Class}

 _{Classes or priorities of packet}  _{Still under development}

 _{See RFC 2460}  _{Flow Label}

 _{Used by hosts requesting special handling}  _{Payload length}

 _{Includes all extension headers plus user}

IP v6 Header Fields (2)

 _{Next Header}

 _{Identifies type of header}

 _{Extension or next layer up}  _{Source Address}

IPv6 Addresses

 _{128 bits long}

 _{Assigned to interface}

 _{Single interface may have multiple unicast}

addresses

Types of address

 _Unicast

 _{Single interface}  _Anycast

 _{Set of interfaces (typically different}

nodes)

 _{Delivered to any one interface}  _{the “nearest”}

 _Multicast

 _{Set of interfaces}

Hop-by-Hop Options

 _{Next header}

 _{Header extension length}  _Options

 _{Jumbo payload}

 _{Over 2}16 = 65,535 octets  _{Router alert}

 _{Tells the router that the contents of}

this packet is of interest to the router

 _{Provides support for RSPV (chapter}

Fragmentation Header

 _{Fragmentation only allowed at source}

 _{No fragmentation at intermediate routers}  _{Node must perform path discovery to find}

smallest MTU of intermediate networks

Fragmentation Header Fields

 _{Next Header}  _Reserved

 _{Fragmentation offset}  _Reserved

 _{More flag}

Routing Header

 _{List of one or more intermediate nodes to}

be visited

 _{Next Header}

 _{Header extension length}  _{Routing type}

 _{Segments left}

Destination Options

 _{Same format as Hop-by-Hop options}

Multicasting

 _{Addresses that refer to group of hosts on}

one or more networks

 _Uses

 _{Multimedia “broadcast”}  _{Teleconferencing}

 _Database

Broadcast and Multiple Unicast

 _{Broadcast a copy of packet to each}

network

 _{Requires 13 copies of packet}  _{Multiple Unicast}

 _{Send packet only to networks that have}

hosts in group

True Multicast

 _{Determine least cost path to each network}

that has host in group

 _{Gives spanning tree configuration}

containing networks with group members

 _{Transmit single packet along spanning tree}  _{Routers replicate packets at branch points}

of spanning tree

Requirements for

Multicasting (1)

 _{Router may have to forward more than one}

copy of packet

 _{Convention needed to identify multicast}

addresses

 _{IPv4 - Class D - start 1110}

 _{IPv6 - 8 bit prefix, all 1, 4 bit flags field, 4 bit} scope field, 112 bit group identifier

 _{Nodes must translate between IP multicast}

addresses and list of networks containing group members

 _{Router must translate between IP multicast}

Requirements for

Multicasting (2)

 _{Mechanism required for hosts to join and}

leave multicast group

 _{Routers must exchange info}

 _{Which networks include members of given}

group

 _{Sufficient info to work out shortest path to}

each network

 _{Routing algorithm to work out shortest}

path

 _{Routers must determine routing paths}

IGMP

 _{Internet Group Management Protocol}  _{RFC 1112}

 _{Host and router exchange of multicast}

group info

 _{Use broadcast LAN to transfer info among}

IGMP Fields

 _Version  ₁

 _Type

 _{1 - query sent by router}  _{O - report sent by host}  _Checksum

 _{Group address}

 _{Zero in request message}

IGMP Operation

 To join a group, hosts sends report message

 _{Group address of group to join}

 _{In IP datagram to same multicast}

destination address

 _{All hosts in group receive message}

 _{Routers listen to all multicast addresses to}

hear all reports

 _{Routers periodically issue request message}

 _{Sent to all-hosts multicast address}

 _{Host that want to stay in groups must}

Group Membership in IPv6

 _{Function of IGMP included in ICMP v6}  _{New group membership termination}

Required Reading

 _{Stallings chapter 15}

 _{Comer, S. Internetworking with TCP/IP,}

volume 1, Prentice-Hall

 _{All RFCs mentioned plus any others}

connected with these topics

 _{Loads of Web sites on TCP/IP and IP}