Protocol Architectures IP Framework

Going, Going…..

Course so far

•  Basic OS principles •  Networks - Ethernet •  Network devices in Linux •  Looked at socket code and basic socket

calls •  Looked at the select socket call

– Call allows us to wait on a set of sockets – Alternative to forking another process or multi-

threading

Need to take a step back

•  Moved from the OS to networking side. •  Need to spend some time giving you a

networking context •  Most communication models done using the

Open System Interconnection (OSI) model

OSI Model

Physical Layer

Data Link Layer

Network Layer

Transport Layer

Session Layer

Presentation Layer

Application Layer

OSI Model Explained

•  Used as a reference model for computer communications. It is NOT an implementation model

•  Physical Layer - interfaces with the physical medium. Decides things like what is a 1 and what is a 0.

OSI cont’d •  Data Link Layer - How data units are sent

and received between two adjacent nodes. –  Deals with things like how endpoints are

addressed. How the packet is framed and error detection and recovery

•  Network Layer - Exchange of data between two machines over a network. – How machines are addressed in the network.

Packets need to go through gateways and routers. May involve setting up, maintaining or clearing connections between endpoints

OSI Model •  Transport Layer - Concerned with moving

data between two endpoints (usually two processes) over a network –  Issues of reliability, error detection and

recovery as well as Quality-Of-Service issues •  Session Layer - structures to support a

session - as a series of related interactions between endpoints. – Request/Response interaction - Client /Server;

PUSH/PULL models, how individual sessions are setup, maintained and closed

OSI Model Cont’d

•  Presentation Layer - Identifying structures and items in the data stream that help the application use it in a structured way – Moving from structures to bits and back again

•  Application Layer - Provides an interface for the application to use the OSI model

IPv4 Header

32-bit source IP address

32-bit destination IP address

TOS TOTAL LENGTH IHL V

16-bit IDENTIFIER Flags 13-bit Frag Offset

TTL PROTO NO

16-bit header checksum

Options (if any)

IPv4 continued

•  V = version number = 4 •  IHL = IP header length in 32 bits = 5 •  TOS = Type of Service Field

–  used to specify quality-of-service requirements •  TOTAL LENGTH = total length of packet •  IDENTIFIER = uniquely identifies the

packet in a set

IPv4 continued

•  Flags - used to help packet fragmentation •  FRAG OFF - identifiers the offset where

this packet is located as part of a large packet

•  TTL - Time to live field –  may be set to different values; decremented

every time packet passes router. If zero, packet is deleted. Stops packets looping around endlessly

IPv4 continued

•  PROTO_NO - specifies the transport protocol running over IP – TCP = 6, UDP = 17

•  HEADER CHECKSUM - every header is first checksummed if error entire packet is discarded

•  32 -bit source and destination addresses

IPv6 Header Format Version Traffic

Class Flow Label

Payload Length Next header Hop Limit

Source Address

Destination Address

IPv6 Field Formats

•  Much simpler than IPv4 •  Version field (4)

–  Indicates the version of IP = 6 •  Traffic Class (8)

–  Indicates the type of traffic – Similar to TOS field in IPv4

IPv6 Field Formats •  Flow Label (20)

– Can be used to identify a particular flow between two endpoints

– Can be used to provide per flow support •  Authentication, Priority

•  Payload length (16) – Excludes the IPv6 header but includes

additional Headers

IPv6 Field Formats

•  Next Header (8) – Additional Header – Transport Protocol

•  TCP, UDP, etc

•  Hop Limit (8) – Prevents Looping – Similar to TTL in IPv4

IPv6 Field Formats

•  Source Address (128) •  Destination Address (128) •  Huge Address Space

– Divided into several types •  Link Only (machines directly connected) •  Site Only •  Global Addresses

The Aggregatable Global Unicast Address

now obsolete

Interface Identifier SLAID NLAID RES TLAID Pre Fix

Prefix - 3 bits, 001 indicates an aggregatable global unicast address TLAID – 13 bits, Top-Level aggregatable idebtifier RES - 8 bits, Reserved for future use NLAID – 24 bits Next-level aggregatable identifier SLAID – 16 bits, Site-level aggregatable identifier Interface ID – 64 bits, Interface ID, globally unique

Auto-configuration

•  Once we can determine the network that we are attached to, we can automatically get a unique IPv6 address

•  Can do so using Router Advertisement and Neighbour Discovery protocols

•  Eliminates the need for Foreign Agents •  MN communicates directly with HA and

CN about Binding Updates

Header extensions

•  Header extensions can be used to: – Help re-route packets, so avoid the need for

encapsulation – Can also provide security header extensions

which maintain secure connections

TCP header

Options (if any)

16-bit source port no 16-bit destination port no

32-bit sequence number

32-bit acknowledge number

16-bit window size

16-bit urgent pointer

THL FLAGS RESV

16-bit TCP checksum

TCP header

•  16-bit source and destination ports •  32-bit sequence no - refers to bytes sent •  32-bit acknowledge no - acknowledges

bytes received •  THL - TCP header length •  Window size - the number of bytes that the

sender can send to the receiver before waiting for an acknowledgement

TCP header cont’d

•  TCP checksum - includes a pseudo IP header with IP source and destination addresses

•  Urgent Pointer - points the urgent data in the stream

•  RESV - reserved 6 bits

TCP Flags

•  URG - urgent pointer is valid

•  ACK - acknowledgement number is valid

•  PSH - push packet up to application –  end of a very large packet

•  RST - reset packet - drop the connection

TCP Flags Cont’d

•  SYN - synchronize sequence numbers at the start of a connection

•  FIN - the sender is finished sending data

IP world in terms of OSI

Physical Layer

Data Link Layer

Network Layer

Transport Layer

Session Layer

Presentation Layer

Application Layer

Copper, Fibre Twisted par

IPv4, IPv6

TCP, UDP

Sockets

RPC, CORBA Java

Ethernet, Token Ring, 802.11 a/b/g

Mobility now a key issue

•  Mobility is now getting ubiquitous •  Explosion of wireless technologies

– Mobile phones •  2G, 2.5G, 3G ->>> 4G

•  Wireless LANs –  802.11 based on Ethernet technology – Wireless ATM

New Wireless Technology coming

•  Bluetooth – Now very common on PDAs, Laptops

•  UltraWideband (UWB) – New Technology – First deployments

•  802.11n – Now being commonly deployed – Useable data speed about 200 Mbps

Wireless Infrastructure Two Extremes

•  Fixed Wireless System –  Endpoints are fixed but communicate over a wireless

link. •  Ad-hoc systems

–  No fixed infrastructure –  Nodes communicate when they are within range of

each other transmissions. –  MACs for these devices also look at power and ad-hoc

routing. Energy Aware Routing (EAR) protocols.

Mobile Systems •  Mobile Systems – Most common

–  One Endpoint normally fixed and part of the wired network

•  Base stations – usually on hills or on tall buildings –  Other endpoint moves – mobile Laptop, PDA, handset

•  Horizontal Handoff –  Handing off to another base station in the same network –  Most common now

•  Vertical Handoff –  Handoff to a totally different network (e.g. –  Will be common in the future

Main Problem in supporting mobility using IP

•  An IP address provides two key inputs –  It uniquely identifies the endpoint/device to the

network –  It also is used to choose the path to route data

through the network – No inherent support for mobility

Implications for IP

•  If we move from one network to another we need a completely new IP address associated with the new network to communicate

•  However if we are on a completely new network, machines trying to communicate with us will be unaware that we have moved

•  Need more infrastructure to support mobility –  Mobile IPv4

Mobile IPv4 -The Terms

•  Mobile Node (MN) – the mobile device •  Corresponding Node (CN) – the device trying to

communicate with the MN •  Home Network – the network by which the MN is

usually contacted •  Home Agent (HA) – a network entity which keeps

track of the MN’s whereabouts and if the MN is away from its home network, forwards packets to the MN

Mobile IPv4 -The Terms cont’d

•  Foreign Network – the network to which the device is currently connected – NOT its home network

•  Care-of-Address (COA) – The address of the MN on the Foreign Network

•  Foreign Agent (FA)- a network entity which keeps track of a visiting MN from another network

A Typical Setup

Internet

Home Network

Foreign Network CN’s Network

MN

Router HA

Router FA

MN/COA CN’s

Router

CN

Observations

•  HA runs on Router of Home Network •  FA runs on Router of Foreign Network •  COA can be

–  1) A real IP address given to the MN •  Co-location – limited number of IP addresses

–  2) An address managed by the FA •  Not directly allocated to the MN

Problem

•  How does the MN know it is now on a new network

•  Routers advertise their presence on their networks. This is called a Router Advertisement or RA message

•  HAs and FAs must also use messages to advertise their presence (RFC 1526)

RFC 1526 Type Code Checksum

# addresses Addr. Size Lifetime Router Address 1

Preference Level 1

Router Address 2 Preference Level 2

Type Length Sequence Number

COA

COA

Registration Lifetime Reserved R B H F M G V

:: :: :: :: ::

RFC 1526

Static part advertises router interfaces Mobile extension – used to advertise Home and

Foreign Agents H bit says that router can act as a home agent F bit says the router can act as a foreign agent R bit if set tells the MN to register with this agent

rather than getting a co-located address A list of COAs is also advertised

Getting a COA

•  If the MN cannot hear any agent/router advertisements, it sends solicitation messages asking if an agent/router is available

•  It can also try to obtain a co-located COA using standard means such as DHCP

Registration

•  Now that it has a COA the MN must register this information with the Home Agent on its Home network

•  If the COA has been obtained from the FA then the MN first registers with the FA and the FA in turn registers with the HA.

Registration Request 0 31

Type Flags Lifetime

Home Address

Home Agent

COA

Identification

What happens at the HA

•  When HA receives a registration request: – Sets up a mobility binding which maps the

COA to the Home address of the MN – Sends a registration reply – All packets addressed to the MN using its

Home Address are now tunnelled to MN using its COA address.

Registration MN/COA FA HA

Registration

Registration

Mobility Binding

Registration Reply Registration Reply

Mobile IPv4 Communication

between MN and CN

MN/COA

CN

Router HA

Secure Tunnel

Different Tunnelling Schemes

•  IP-in-IP tunnelling – Outer IP header

•  Src = IP address of the HA •  Dest = IP address of the COA

–  Inner IP header •  Src = IP Address of the CN •  Dest = IP Address of the MN at home

Other Encapsulation Schemes

•  Minimum Encapsulation –  Instead of using 2 IP headers we include the

two sets of addresses but eliminate the redundant bits - (M bit is set in RFC 1526)

•  GRE Encapsulation – Supported by Cisco – Allows packets from one protocol suite to be

encapsulated using another protocol – (G bit is set in RFC 1526)

Big Problem

•  If I, from the UK, go to a conference in Australia; at the conference I meet some one from France and we want to communicate using the Wireless LAN that has been set up for the conference.

•  Packets get sent from Australia to France and the UK respectively and then back to Australia again

Route Optimisation

•  Instead of sending data packets to the HA, the CN makes a Binding Request which asks for the COA of the MN. If OK, then the HA sends back current mobility binding for the MN

•  The CN keeps a binding cache which is integrated with its routing table

Binding Update Protocol

•  As the MN moves, it issues a Binding Update Message to its HA so that data can be sent to the new location

•  Binding Updates (BU) can also be acknowledged to ensure that they have been received

•  Binding Warning: If the MN moves to a new FA but packets are still being sent to the old FA, then a Binding Warning is sent back to the HA. The HA then informs the CN that the FA has been changed

CN HA FA_old MN FA_new Request

Update

ACK

MN moves

Data Data

Data

Data

Registration

Registration

Data Warning

Update

ACK

Update

ACK

Data Data

ROUTE OPTIMISATION – MOBILE IPv4

Verdict: Too complicated

•  Binding Updates need to be communicated securely so that the MN movements are not tracked. Points to some sort of encryption

•  Firewall and VPN issues as the MN moves around

•  Is Mobile IPv6 any better?

CN HA MN

Request

Update

ACK

MN moves

Data

Update

Update

ACK

ACK

Data

ROUTE OPTIMISATION – IPv6

Sources for this Lecture

•  Internetworking with TCP/IP Volume III by Douglas Comer and David Stevens

•  http://www.protocols.com A key site to find out about protocols and protocol stacks