Network Layer4-1 Part of slides provided by J.F Kurose and K.W. Ross, All Rights Reserved Chapter 4 Network Layer Communication Networks P. Demeester

Network Layer 4-1

Part of slides provided by J.F Kurose and K.W. Ross, All Rights Reserved

Chapter 4Network Layer

Communication NetworksP. Demeester

Computer networking -A top-down approach featuring the internet4th Edition, 2008Addison WesleyJames F. Kurose, Keith W. RossISBN 0-321-49770-8

Network Layer 4-2

Chapter 4 outline

4.1 Introduction and Network Service Models4.2 Routing Principles4.3 Hierarchical Routing4.4 The Internet (IP) Protocol4.5 Routing in the Internet4.6 What’s Inside a Router4.7 IPv64.8 Multicast Routing4.9 Mobility

Network Layer 4-3

transport packet from sending to receiving hosts

network layer protocols in every host, router

three important functions: path determination: route

taken by packets from source to dest. Routing algorithms

forwarding: move packets from router’s input to appropriate router output

call setup: some network architectures require router call setup along path before data flows

networkdata linkphysical








application

transportnetworkdata linkphysical

application


Network layer functions

Network Layer 4-4

A B

C

D

E

Y:to BZ:to D Y:to C

Z:to E

Y:to Y

Source : XDestination : YContent : TCP

Storeand

Forward

RoutingTable

Buffer

Router

Link

computerhost

terminal

W

X

Y

Z

Network layer functions : IP forwarding

Network Layer 4-5

no call setup at network layer routers: no state about end-to-end connections

no network-level concept of “connection”

packets forwarded using destination host address packets between same source-dest pair may take

different paths

application


application


1. Send data 2. Receive data

Datagram networks: the Internet model

Network Layer 4-6

End-to-end Packet delivery service Unreliable, but an honest attempt Best-effort, no Quality of Service

(QoS)(no guarantee on delay or bandwidth)

Designed for internetworking (over any L2)

Connectionless

The IP Service

Network Layer 4-7

Chapter 4 outline

4.1 Introduction and Network Service Models4.2 Routing Principles4.3 Hierarchical Routing

4.4 The Internet (IP) Protocol 4.4.1 IPv4 addressing 4.4.2 Moving a datagram from source to

destination 4.4.3 Datagram format 4.4.4 IP fragmentation 4.4.5 ICMP: Internet Control Message Protocol 4.4.6 DHCP: Dynamic Host Configuration Protocol 4.4.7 NAT: Network Address Translation

4.5 Routing in the Internet4.6 What’s Inside a Router4.7 IPv64.8 Multicast Routing4.9 Mobility

Network Layer 4-8

Chapter 4 outline


destination 4.4.3 Datagram format 4.4.4 IP fragmentation 4.4.5 ICMP: Internet Control Message

Protocol 4.4.6 DHCP: Dynamic Host Configuration

Protocol 4.4.7 NAT: Network Address Translation

Network Layer 4-9

forwardingtable

Host, router network layer functions:

Routing protocols•path selection•RIP, OSPF, BGP

IP protocol•addressing conventions•datagram format•packet handling conventions

ICMP protocol•error reporting•router “signaling”

Transport layer: TCP, UDP

Link layer

physical layer

Networklayer

The Internet Network layer

Network Layer 4-10

[0.0.0.0-128.0.0.0[HP : 15.0.0.0

128 networks16 million addr/network

16k networks64k addr/network

2 M networks, 256 addr/network

IP address format : 4 octets, decimal notation, separation by dotexample : 157.193.122.10range : 0 - 255 (corresponds to 0000 0000 - 1111 1111 or 00-FF)

Two parts : network part and host part

Class A 0 Network Host

Class B 10 Network Host

Class C 110 Network Host

Class D 1110 Multicast address

Class E 11110 Reserved for future use

[128.0.0.0-192.0.0.0[UGent : 157.193.0.0

address space

157.193.122.10

network host

UGent network : 157.193 (64k hosts)

Address Format - Address Classes

Network Layer 4-11

X.Y.0.0 : notation for a networkexamples : 15.0.0.0 (class A network), 157.193.0.0 (class B network), 193.125.97.0 (class C network)

127.X.Y.Z : loopback Interface (for debugging)in practice mainly 127.0.0.1 address used

0.0.0.0 : this host on this network (used for booting)only allowed as source address

0.0.X.Y : a host on this network (used for booting)only allowed as source address

255.255.255.255 : broadcast to all hosts on this networkonly allowed as destination address, no forwarding allowed

X.Y.255.255 : broadcast to all hosts on a remote networkonly allowed as destination address

A network, subnetwork or host can NEVER consist entirely of 0’s or 1’s

10.0.0.0-10.255.255.255; 172.16.0.0-172.31.255.255; 192.168.0.0-192.168.255.255 :

used for networks not connected to The Internet (e.g. private internets)

Special Addresses

Network Layer 4-12

Router Plateau(ftwe)

157.193.103.254

eduserv2157.193.40.10

eduserv1157.193.40.9

157.193.40.254

157.193.227.1

Router Belnet(belnet)

157.193.227.2

Router ARC(rtr-arc)

157.193.234.2

157.193.234.1

Router Technicum(rtr-tech)157.193.60.254

157.193.60.31

ftwe01157.193.103.1

ftwe02 157.193.103.2

ftwe51 157.193.103.51

PC room Plateau

Belnet backbone

Example : UGent network

Network Layer 4-13


157.193.103.254

eduserv2157.193.40.10

eduserv1157.193.40.9

157.193.40.254

157.193.227.1


157.193.227.2

Router ARC(rtr-arc)

157.193.234.2

157.193.234.1


157.193.60.31

ftwe01157.193.103.1

ftwe02 157.193.103.2

ftwe51 157.193.103.51

PC room Plateau

Belnet backbonedirect connected network

direct connected network



direct connecte

d network

Direct connected networks

Network Layer 4-14


157.193.103.254

eduserv2157.193.40.10

eduserv1157.193.40.9

157.193.40.254

157.193.227.1


157.193.227.2

Router ARC(rtr-arc)

157.193.234.2

157.193.234.1


157.193.60.31

ftwe01157.193.103.1

ftwe02 157.193.103.2

ftwe51 157.193.103.51

PC room Plateau

Belnet backbone

Subnetwork157.193.40.0

Subnetwork157.193.227.

0

Subnetwork

157.193.60.0

Subnetwork157.193.234.

0

Subnetwork157.193.103.0network

subnetworkhost

Subnetworks

Network Layer 4-15

0 0 0 0…0 0 0 0

HostWith subnetting Network Subnet

Subnet mask 1 1 1 1 1 …1 1 1 1 1 1 1 1 1 1 1 1

Subnetwork : 157.193.103.0 (mask FF.FF.FF.00)network part : 157.193 (class B)subnetwork part : 103 (8 bits, 254 subnets)mask used : FF.FF.FF.0000 0000# hosts : 254 (00 and FF not allowed)host range : 157.193.103.1 - 157.193.103.254

Subnetwork : 158.78.42.64 (mask FF.FF.FF.C0)network part : 158.78 (class B)subnetwork part: 00101010.01 (10 bits, 1022 subnets)mask used : FF.FF.FF.1100 0000# hosts : 62 (00 0000 and 11 1111 not allowed)host range : 158.78.42.65 - 158.78.42.126

Note : binary, decimal and hexadecimal notation used where appropriate

Subnetwork : 158.78.01.00 (mask FF.FF.FF.C0)host range : 158.78.01.01 - 158.78.01.62

Without subnetting HostNetwork

BORDER SUBNET | HOST

Subnet addressing in IP

Network Layer 4-16

Subnetwork : 157.193.0.0 (mask FF.FF.FF.00) : NOT ALLOWEDsubnetwork = all 0’s not allowed because no distinction withthe class B address 157.193.0.0 (in practice : used)

Subnetwork : 157.193.255.0 (mask FF.FF.FF.00) : NOT ALLOWEDsubnetwork = all 1’s not allowed (in practice : used)

SUBNET BITS

# OF SUBNETS

HOST BITS # OF

HOSTS MASK

0 0 16 65534 255.255.0.0

1 - 15 - not allowed

2 2 14 16382 255.255.192.0

3 6 13 8190 255.255.224.0

4 14 12 4096 255.255.240.0

5 30 11 2046 255.255.248.0

… … … … …

11 2046 5 30 255.255.255.224

12 4094 4 14 255.255.255.240

13 8190 3 6 255.255.255.248

14 16382 2 2 255.255.255.252

15 - 1 - not allowed

class B subnetworks

Subnet addressing in IP : class B

Network Layer 4-17

subnetmask (CIDR) /24 /25 /26 /27 /28 /29 /30subnetmask (DEC) 0 .128 .192 .224 .240 .248 .252subnetmask (HEX) .00 .80 .C0 .E0 .F0 .F8 .FC

0 255 0 127 0 63 0 31 0 15 0 7 0 34 7

8 15 8 1112 15

16 31 16 23 16 1920 23

24 31 24 2728 31

32 63 32 47 32 39 32 3536 39

40 47 40 4344 47

48 63 48 55 48 5152 55

56 63 56 5960 63

64 127 64 95 64 79 64 71 64 6768 71

72 79 72 7576 79

80 95 80 87 80 8384 87

88 95 88 9192 95

96 127 96 111 96 103 96 99100 103

104 111 104 107108 111

112 127 112 119 112 115116 119

120 127 120 123124 127

128 255 128 191 128 159 128 143 128 135 128 131132 135

136 143 136 139140 143

144 159 144 151 144 147148 151

152 159 152 155156 159

160 191 160 175 160 167 160 163164 167

168 175 168 171172 175

176 191 176 183 176 179180 183

184 191 184 187188 191

192 255 192 223 192 207 192 199 192 195196 199

200 207 200 203204 207

208 223 208 215 208 211212 215

216 223 216 219220 223

224 255 224 239 224 231 224 227228 231

232 239 232 235236 239

240 255 240 247 240 243244 247

248 255 248 251252 255

Subnet addressing in IP : class C

Network Layer 4-18

subnetmask (CIDR) /24 /25 /26 /27 /28 /29 /30subnetmask (DEC) 0 .128 .192 .224 .240 .248 .252subnetmask (HEX) .00 .80 .C0 .E0 .F0 .F8 .FC

0 255 0 127 0 63 0 31 0 15 0 7 0 34 7

8 15 8 1112 15

16 31 16 23 16 1920 23

24 31 24 2728 31

32 63 32 47 32 39 32 3536 39

40 47 40 4344 47

48 63 48 55 48 5152 55

56 63 56 5960 63

64 127 64 95 64 79 64 71 64 6768 71

72 79 72 7576 79

80 95 80 87 80 8384 87

88 95 88 9192 95

96 127 96 111 96 103 96 99100 103

104 111 104 107108 111

112 127 112 119 112 115116 119

120 127 120 123124 127

128 255 128 191 128 159 128 143 128 135 128 131132 135

136 143 136 139140 143

144 159 144 151 144 147148 151

152 159 152 155156 159

160 191 160 175 160 167 160 163164 167

168 175 168 171172 175

176 191 176 183 176 179180 183

184 191 184 187188 191

192 255 192 223 192 207 192 199 192 195196 199

200 207 200 203204 207

208 223 208 215 208 211212 215

216 223 216 219220 223

224 255 224 239 224 231 224 227228 231

232 239 232 235236 239

240 255 240 247 240 243244 247

248 255 248 251252 255

Subnet addressing class C : example

Network Layer 4-19

IF

(destination_address AND subnet_mask)==(my_address AND subnet_mask)

THEN

destination host is on a directly connected network

ELSE

the packet must be sent to a router firstPacket to 157.193.102.51

AND with FF.FF.FF.00gives : 157.193.102.0

==157.193.102.3

AND with FF.FF.FF.00gives : 157.193.102.0

==> LOCAL HOST

Packet to 157.193.103.12AND with FF.FF.FF.00gives : 157.193.103.0

NOT ==157.193.102.3

AND with FF.FF.FF.00gives : 157.193.102.0==> GO TO ROUTER

router

157.193.102.3

157.193.102.254

157.193.102.51


157.193.103.12

157.193.103.254


subnet mask : FF.FF.FF.00 note : ARP

Subnet addressing in IP : Example

Network Layer 4-20

Classful addressing: inefficient use of address space, address space

exhaustion e.g., class B net allocated enough addresses for 65K

hosts, even if only 2K hosts in that network

CIDR: Classless InterDomain Routing network portion of address of arbitrary length address format: a.b.c.d/x, where x is # bits in network

portion of address

11001000 00010111 00010000 00000000

networkpart

hostpart

200.23.16.0/23

IP addressing: CIDR

Network Layer 4-21

Q: How does host get IP address?

hard-coded by system admin in a file Wintel: control-panel->network-

>configuration->tcp/ip->properties UNIX: /etc/rc.config

DHCP: Dynamic Host Configuration Protocol: dynamically get address from as server “plug-and-play”

(more shortly)

IP addresses: how to get one?

Network Layer 4-22

Q: How does network get network part of IP addr?

A: gets allocated portion of its provider ISP’s address space

ISP's block 11001000 00010111 00010000 00000000 200.23.16.0/20

Organization 0 11001000 00010111 00010000 00000000 200.23.16.0/23 Organization 1 11001000 00010111 00010010 00000000 200.23.18.0/23 Organization 2 11001000 00010111 00010100 00000000 200.23.20.0/23 ... ….. …. ….

Organization 7 11001000 00010111 00011110 00000000 200.23.30.0/23

IP addresses: how to get one?

Network Layer 4-23

“Send me anythingwith addresses beginning 200.23.16.0/20”

200.23.16.0/23

200.23.18.0/23

200.23.30.0/23

ISP - Belnet

Organization 0

Organization 7Internet

Organization 1

ISP - Newnet “Send me anythingwith addresses beginning 199.31.0.0/16”

200.23.20.0/23Organization 2

...

...

Hierarchical addressing allows efficient advertisement of routing information:

Hierarchical addressing: route aggregation

Network Layer 4-24

ISPs - Newnet has a more specific route to Organization 1

“Send me anythingwith addresses beginning 200.23.16.0/20”

200.23.16.0/23

200.23.18.0/23

200.23.30.0/23

ISP - Belnet

Organization 0

Organization 7Internet

Organization 1

ISP - Newnet“Send me anythingwith addresses beginning 199.31.0.0/16or 200.23.18.0/23”

200.23.20.0/23Organization 2

...

...

Hierarchical addressing: more specific routes

Network Layer 4-25

Q: How does an ISP get block of addresses?

A: ICANN: Internet Corporation for Assigned

Names and Numbers allocates addresses manages DNS assigns domain names, resolves disputes

IP addressing: the last word...

www.icann.org

Exc.1

Network Layer 4-26

Chapter 4 outline

4.4 The Internet (IP) Protocol 4.4.1 IPv4 addressing 4.4.2 Moving a datagram from

source to destination : forwarding 4.4.3 Datagram format 4.4.4 IP fragmentation 4.4.5 ICMP: Internet Control Message



Network Layer 4-27

• IP packet arrives in a router (store in a buffer)• Header is analyzed : what is the destination IP address• Look-up of the routing table : next hop (or local)• Forward packet to the correct interface

(or deliver to local application)

Routing table : Destination Next hop A LAN 2 B LAN 3

A

AA

LAN 1

LAN 2

LAN 3

A

B

Router : Store and Forward

Network Layer 4-28Cisco 12000 series

Router Examples

Network Layer 4-29

router A

LAN 2


157.193.102.254

157.193.103.254

157.193.104.254

157.193.102.253

LAN 1


157.193.102.1

157.193.103.1

157.193.104.1

157.193.102.34

Routing table router A

router B

INTERNET

LA

N 3


Destination Mask Gateway Interface

127.0.0.0 FF.00.00.00 127.0.0.1 Lo0

0.0.0.0 0.0.0.0 157.193.102.253

LAN 1

157.193.102.0 FF.FF.FF.00 157.193.102.254

LAN 1

157.193.103.0 FF.FF.FF.00 157.193.103.254

LAN 2

157.193.104.0 FF.FF.FF.00 157.193.104.254

LAN 3

Destination Gateway Interface

127.0.0.0/8 127.0.0.1 127.0.0.1

0.0.0.0/0 157.193.102.253

157.193.102.254

157.193.102.0/24

157.193.102.254

157.193.102.254

157.193.103.0/24

157.193.103.254

157.193.103.254

157.193.104.0/24

157.193.104.254

157.193.104.254

Routing Table : example

Network Layer 4-30


157.193.103.254

eduserv2157.193.40.10

eduserv1157.193.40.9

157.193.40.254

157.193.227.1


157.193.227.2

Router ARC(rtr-arc)

157.193.234.2

157.193.234.1


157.193.60.31

ftwe01157.193.103.1

ftwe02 157.193.103.2

ftwe51 157.193.103.51

PC room Plateau

Belnet backbone

lan0

lan1 hme0

Routing table for a host (eduserv2)Destination Gateway Interface

127.0.0.1 127.0.0.1 lo0

157.193.40.0 157.193.40.10 hme0

default 157.193.40.254 hme0

Routing table for an edge router (ftwe)Destination Gateway Interface127.0.0.1 127.0.0.1 lo0157.193.103.0 157.193.103.254 lan0157.193.60.0 157.193.60.31 lan1default 157.193.60.254 lan1

Routing Table : Example UGent network

Network Layer 4-31

allserv:/staff/ftwe/pdemeest$ netstat -rn

Routing Table: Destination Gateway Flags Ref Use Interface-------------------- -------------------- ----- ----- ------ ---------157.193.40.0 157.193.40.42 U 3 63929 hme0224.0.0.0 157.193.40.42 U 3 0 hme0default 157.193.40.254 UG 028820629127.0.0.1 127.0.0.1 UH 07349737 lo0

allserv:/staff/ftwe/pdemeest$ netstat -r

Routing Table: Destination Gateway Flags Ref Use Interface-------------------- -------------------- ----- ----- ------ ---------157.193.40.0 allserv.rug.ac.be U 3 63857 hme0BASE-ADDRESS.MCAST.NET allserv.rug.ac.be U 3 0 hme0default rtr-arc.rug.ac.be UG 028790639localhost localhost UH 07347592 lo0

C:\WINDOWS>netstat -rRoute TableActive Routes: Network Address Netmask Gateway Address Interface Metric 0.0.0.0 0.0.0.0 157.193.122.1 157.193.122.201 1 127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1 157.193.122.0 255.255.255.0 157.193.122.201 157.193.122.201 1 157.193.122.201 255.255.255.255 127.0.0.1 127.0.0.1 1 157.193.255.255 255.255.255.255 157.193.122.201 157.193.122.201 1 224.0.0.0 224.0.0.0 157.193.122.201 157.193.122.201 1 255.255.255.255 255.255.255.255 157.193.122.201 157.193.122.201 1

Flags : U : route is upG : route to a gateway (if not set : directly connected destination)H : route to a host (if not set : route to a network)

Routing Table : examples

Network Layer 4-32

Sanity checks: version number and header checksum decrement TTL (if reduced to 0 ==> discard)

Match destination address with: own addresses (no forwarding needed) prefix(es) in the routing table (longest match)

Routing table : 157.193.84.0 direct lan1157.193.0.0 157.193.234.2 lan2

destination: 157.193.84.20: longest prefix match is 157.193.84 => lan1(note : also 157.193 is a prefix match, but not the longest)

destination: 157.193.85.20: longest prefix match is 157.193 => lan2

Send to outgoing interface: fragment if packet size > MTU (Maximum Transfer Unit)

recalculate header checksum

The Forwarding Process

Network Layer

R1

R2R4

R3

UK Backbone

Dutch Backbone

Belgian BackboneBELNET

193.190.19x.0

KULeuvenBackbone134.58.0.0

UGent BackboneRUGNET

157.193.0.0

GermanBackbone

French Backbone

European BackboneTransatlantic

European Backbone Router : • entries to directly attached networks (e.g. BELNET)• entries to every network attached to these directly attached networks

(e.g.: BELNET : UGent, KULeuven, VUB, … backbone)• entries to every network in US (unless default)

Large Router : • up to 40.000 entries in routing table• long search for appropriate entry• stability of routing protocols

(many routes to be advertised)

The Routing Table in a Large Network

Network Layer 4-34

UGent : 1997

Network Layer 4-35

subnet : 157.193.188.0 (FF.FF.FF.00)

.6

.1.2 .3

.4 .5

.7.8

.9

.10

.11

.12

.13

.122.0.184.0

.138

.0rtr-urb

.155.0.149

.0

tacitusheraURBIS

UGent : 2000

Network Layer 4-36

UGent : 2003

Network Layer 4-37

BELNET Backbone

Network Layer 4-38

BELNET Backbone

Network Layer 4-39

GEANT Backbone

Exc.2

Network Layer 4-40





Chapter 4 outline

Network Layer 4-41

IP Packet Format

4-bitversion

4-bitheaderlength

8-bit ToS 16-bit total length of packet

16-bit identification 3-bit flags 13-bit fragmentoffset

8-bit TTL 8-bit protocol 16-bit header checksum32-bit source IP address

32-bit destination IP address

Options (if any)

Data

Identification of each packetsend by host

(increment each time packet is sent)

Used for fragmentation

Time-To-Live : start at 32 or 64

decrement at each hopdiscard packet if TTL=0

32 bit source and destination address

Not often used (timestamp, route to follow, …)

Calculated over headersimilar to TCP

Indicate higher layer protocol1 Internet Control Message Prot. ICMP2 Internet Group Management Prot.IGMP4 IP-in-IP tunnelling IP-in-IP6 Transmission Control ProtocolTCP17 User Datagram Protocol UDP46 Resource Reservation ProtocolRSVP89 Open Shortest Path First OSPF

Number of 32 bit words(if no options : 5)

Number of bytes in IP packet(including header)

maximum of 65535 bytestypical few 100 to few 1000

Type of Service3 bits for priority

4 bits for delay, BW, …1 bit reserved

NOT USED

Currently : IP version 4 or IPv4also IPv6

Network Layer 4-42

Chapter 4 outline





Network Layer 4-43

network links have MTU (max.transfer size) - largest possible link-level frame. different link types,

different MTUs large IP datagram divided

(“fragmented”) within network one datagram becomes

several datagrams “reassembled” only at

final destination IP header bits used to

identify, order related fragments

fragmentation: in: one large datagramout: 3 smaller datagrams

reassembly

IP Fragmentation & Reassembly

Network Layer 4-44

ID=x

offset=0

fragflag=0

length=4000

ID=x

offset=0

fragflag=1

length=1500

ID=x

offset=1480

fragflag=1

length=1500

ID=x

offset=2960

fragflag=0

length=1040

One large datagram becomesseveral smaller datagrams

Example 4000 byte

datagram MTU = 1500 bytes

Note : - offset should be multiple of 8 (because encoded in 13 bits)- for offset : do not take header into account

IP Fragmentation and Reassembly

Header (20 bytes)

Network Layer 4-45

Chapter 4 outline


destination 4.4.3 Datagram format 4.4.4 IP fragmentation 4.4.5 ICMP: Internet Control

Message Protocol 4.4.6 DHCP: Dynamic Host Configuration


Network Layer 4-46

ICMP : Internet Control Message Protocol

ICMP resolves the following questions : • What happens after a router crashed and disrupted the network• What notice is given that datagrams are wandering around until their Time-To-Live (TTL) expires ?• What warning is given to the application when sending information to an unreachable host ?• How to know neighbors (routers) ?• ...• How can we know that a host is up and running ?• ...

ICMP messageIP-header

IP-datagram

ICMP is often considered part of the IP layer

protocol =1

Network Layer 4-47

0 8 9 15 16 31

type code checksum

message content (depends on type and code)

QUERY : type = 0, code = 0 : echo reply (ping reply)type = 8, code = 0 : echo request (ping request)type = 9, code = 0 : router advertisementtype = 10, code = 0 : router solicitation...

ERROR : type = 3 : destination unreachable

code = 0 : network unreachablecode = 1 : host unreachablecode = 2 : protocol unreachablecode = 3 : port unreachablecode = 4 : fragmentation needed but don’t-fragment bit set…

type = 5 : redirectcode = 0 : redirect for networkcode = 1 : redirect for host…

type = 11 : time exceededcode = 0 : TTL = 0 during transitcode = 1 : TTL = 0 during reassembly

ICMP Message

Network Layer 4-48

C:\WINDOWS>pingUsage: ping [-t] [-a] [-n count] [-l size] [-f] [-i TTL] [-v TOS] [-r count] [-s count] [[-j host-list] | [-k host-list] [-w timeout] destination-listOptions: -t Ping the specifed host until interrupted. -a Resolve addresses to hostnames. -n count Number of echo requests to send. -l size Send buffer size. -f Set Don't Fragment flag in packet. -i TTL Time To Live. -v TOS Type Of Service. -r count Record route for count hops. -s count Timestamp for count hops. -j host-list Loose source route along host-list. -k host-list Strict source route along host-list. -w timeout Timeout in milliseconds to wait for each reply.

0 8 9 15 16 31

type code checksum

data

sequence numberidentifier

C:\WINDOWS>ping www.kpn.com

Pinging www.kpn.com [145.7.233.150] with 32 bytes of

Reply from 145.7.233.150: bytes=32 time=93ms TTL=239Reply from 145.7.233.150: bytes=32 time=55ms TTL=239Reply from 145.7.233.150: bytes=32 time=54ms TTL=239Reply from 145.7.233.150: bytes=32 time=59ms TTL=239

allserv:/staff/ftwe/pdemeest$ ping -s www.kpn.comPING www.kpn.com: 56 data bytes64 bytes from www.kpn.com (145.7.233.150): icmp_seq=0. time=24. ms64 bytes from www.kpn.com (145.7.233.150): icmp_seq=1. time=28. ms64 bytes from www.kpn.com (145.7.233.150): icmp_seq=2. time=28. ms

ICMP Ping Request

ICMP Ping Reply

ICMP query : Echo (and use in ping)

Network Layer 4-49

157.193.122.0

0 8 9 15 16 31

type = 5 code checksum

IP header + 8 data octets of original datagram

address of router to be used

1 : first packet

3 : ICMP redirect

2 : forward first packet

4 : next packets

157.193.184.0

.51

.1 .2

Send IP packet to 157.193.184.24

Routing Table :default 157.193.138.2157.193.138.0 157.193.138.1157.193.122.0 157.193.122.1157.193.184.0 157.193.122.2

Routing Table :default 157.193.122.1157.193.122.0 157.193.122.51157.193.184.24 157.193.122.2

157.193.122.2

A B

a.o.: 157.193.184.24

INTERNET

157.193.138.1

157.193.138.2

ICMP error : Redirect

Network Layer 4-50

GOAL : find-out the route to a destination (and some additional info)• host running traceroute sends UDP IP-packet to destination with TTL = 1• first router : decrement TTL to 0, discard packet, ICMP time exceeded back• hosts sends UDP IP-packet to destination with TTL = 2• first router : decrement TTL to 1, second router : decrement TTL to 0, discard packet, ICMP time exceeded back• ...allserv:/staff/ftwe/pdemeest$ traceroute www.intec.rug.ac.betraceroute to intecsrv.rug.ac.be (157.193.92.92), 30 hops max, 40 byte packets 1 rtr-arc.rug.ac.be (157.193.40.254) 1 ms 1 ms 1 ms 2 rtr-tech.rug.ac.be (157.193.138.10) 1 ms 1 ms 1 ms 3 intecsrv.rug.ac.be (157.193.92.92) 4 ms 1 ms 3 ms

TTL router name router IP-address roundtrip time (3x)

IP/UDP TTL=1ICMP Time Exceeded

rtr-arc

allserv rtr-arc rtr-tech intecsrv

ICMP error : Time Exceeded use in traceroute

Network Layer 4-51

Chapter 4 outline

4.4 The Internet (IP) Protocol 4.4.1 IPv4 addressing 4.4.2 Moving a datagram from source to destination 4.4.3 Datagram format 4.4.4 IP fragmentation 4.4.5 ICMP: Internet Control Message Protocol 4.4.6 DHCP: Dynamic Host

Configuration Protocol 4.4.7 NAT: Network Address Translation

Network Layer 4-52

HOME

INTERNET

157.193.0.1

publicgatewayrouter

157.193.0.254

ADSL(Belgacom) /Cable Modem

(Telenet)

IP address : 157.193.0.1gateway : 157.193.0.254DNS 1 : 145.122.201.1

Ethernet DNS

145.122.201.1

or dynamic configuration :DHCP (Dynamic Host Control Protocol)

Home Network : single PC

Network Layer 4-53

HOME

INTERNET

publicgatewayrouter

157.193.0.254

ADSL(Belgacom) /Cable Modem

(Telenet)

DNS

145.122.201.1

privatenetwork

192.168.0.0

privategatewayrouter

switch

157.193.0.1

192.168.0.2

192.168.0.3

192.168.0.4

192.168.0.1

IP address : 192.168.0.2gateway : 192.168.0.1DNS 1 : 145.122.201.1

Home Network : multiple PC’s

Network Layer 4-54

INTERNET

157.193.0.254

157.193.0.1

192.168.0.2

192.168.0.3

192.168.0.4

192.168.0.1

202.87.122.4

192.168.0.2:1093 => 202.87.122.4:80

157.193.0.1:2012 => 202.87.122.4:80

202.87.122.4:80 => 157.193.0.1:2012

202.87.122.4:80 => 192.168.0.2:1093

Port 2012 == 192.168.0.2:1093

192.168.0.4:1212 => 202.87.122.4:80

157.193.0.1:2015 => 202.87.122.4:80

202.87.122.4:80 => 157.193.0.1:2015

202.87.122.4:80 => 192.168.0.4:1212

Port 2015 == 192.168.0.4:1212

NAT only known addressin Internet !

WWWserver

NAT : Network Address Translation

Network Layer 4-55

Motivation: local network uses just one IP address as far as outside world is concerned: no need to be allocated range of addresses from

ISP: - just one IP address is used for all devices can change addresses of devices in local network

without notifying outside world can change ISP without changing addresses of

devices in local network devices inside local net not explicitly

addressable, visible by outside world (a security plus).

NAT: Network Address Translation

Network Layer 4-56

16-bit port-number field: >60,000 simultaneous connections with a

single LAN-side address! NAT is controversial:

routers should only process up to layer 3 violates end-to-end argument

• NAT possibility must be taken into account by app designers, e.g., P2P applications

address shortage should instead be solved by IPv6

NAT: Network Address Translation

Network Layer 4-57

INTERNET

157.193.0.254

157.193.0.1

192.168.0.2

192.168.0.3

192.168.0.4

192.168.0.1

202.87.122.4

NAT

UserPCNo packets may enter unless in table

Example : WWW server on 192.168.0.2:1321NAT should open port to enter !

Port 80 == 192.168.0.3:1321WWW serverat port 1321

!!! NAT works as firewall !!!

202.87.122.4:4520 => 157.193.0.1:80

202.87.122.4:4520 => 192.168.0.3:1321

NAT : Network Address Translation

Network Layer 4-58

INTERNET

157.193.0.254

157.193.0.1

192.168.0.13

192.168.0.23

192.168.0.42

192.168.0.1

DHCPserver

DHCP request

IP : 192.168.0.13gateway : 192.168.0.1DNS : 145.122.201.1

DNS

145.122.201.1

192.168.0.13

192.168.0.23192.168.0.4

2

Easy configuration of PCs

How do the PCs know the DHCP server ? ==>DHCP discover

DHCP : Dynamic Host Configuration Protocol

Network Layer 4-59

INTERNET

157.193.0.254

157.193.0.1 DHCPserver

DNS

145.122.201.1157.193.0.1

157.193.0.5

IP : 157.193.0.1gateway : 157.193.0.254

DNS : 145.122.201.1

157.193.0.5

reuse of limited number of IP numbers

DHCP : Dynamic Host Configuration Protocol

Network Layer 4-60

Goal: allow host to dynamically obtain its IP address from network server when it joins networkCan renew its lease on address in useAllows reuse of addresses (only hold address while

connected and “on”)Support for mobile users who want to join network

DHCP overview: host broadcasts “DHCP discover” msg DHCP server responds with “DHCP offer” msg host requests IP address: “DHCP request” msg DHCP server sends address: “DHCP ack” msg

DHCP: Dynamic Host Configuration Protocol

Network Layer 4-61

DHCP server: 223.1.2.5arriving client

time

src : 0.0.0.0, 68 dest.: 255.255.255.255,67DHCPDISCOVERyiaddr: 0.0.0.0transaction ID: 654

src: 223.1.2.5, 67 dest: 255.255.255.255, 68DHCPOFFERyiaddrr: 223.1.2.4transaction ID: 654DHCP server ID : 233.1.2.5Lifetime: 3600 secs

src: 0.0.0.0, 68 dest:: 255.255.255.255, 67DHCPREQUESTyiaddrr: 223.1.2.4transaction ID: 655DHCP server ID : 233.1.2.5Lifetime: 3600 secs

src: 223.1.2.5, 67 dest: 255.255.255.255, 68DHCPACKyiaddrr: 223.1.2.4transaction ID: 655DHCP server ID : 233.1.2.5Lifetime: 3600 secs

Standard ports : 67, 68yiaddrr : Your Internet Address

DHCP client-server scenario

Network Layer 4-62

Chapter 4 outline4.1 Introduction and Network Service Models4.2 Routing Principles4.3 Hierarchical Routing4.4 The Internet (IP) Protocol

4.5 Routing in the Internet 4.5.1 Intra-AS routing: RIP and

OSPF 4.5.2 Inter-AS routing: BGP

4.6 What’s Inside a Router?4.7 IPv64.8 Multicast Routing4.9 Mobility

Network Layer 4-63

A B

C

D E

W

X

Y

Y:to B

Destination : Y Forward

RoutingTable ?

Routing : fill in the routing tables of a router,based on centralized or distributed calculationof a shortest route or distance between router and destination network

Forwarding : forward the packets, based on the destination IP address and the routing table content

distance to Y : 3distance

to Y : 5

shortestroute

Routing <> Forwarding

Network Layer 4-64

Routing in the Internet (hierarchical)

The Global Internet consists of Autonomous Systems (AS, aggregation of routers in regions) interconnected with each other: Stub AS: small corporation: one connection to other AS’s Multihomed AS: large corporation (no transit): multiple

connections to other AS’s Transit AS: provider, hooking many AS’s together

Two-level routing: Intra-AS: administrator responsible for choice of routing

algorithm within network (administrative autonomy), may be different in different AS’s

Inter-AS: unique standard for inter-AS routing: BGP

scale: with 200 million destinations: can’t store all dest’s in routing tables! routing table exchange would swamp links!

Network Layer 4-65

Gateways:•perform inter-AS routing amongst themselves•perform intra-AS routing with other routers in their AS

ab

C

C.b

aB

cb

b

a

Ad c

Intra-AS and Inter-AS routing

A.a

A.c

B.a

inter-AS, intra-AS routing in

gateway A.c

network layer

data link layerphysical layer

Network Layer 4-66

Host h2

a

b

b

aaC

A

Bd c

A.a

A.c

C.bB.a

cb

Hosth1

Intra-AS routingwithin AS A

Inter-AS routingbetween A and B

Intra-AS routingwithin AS B

Intra-AS and Inter-AS routing

Network Layer 4-67

Also known as Interior Gateway Protocols (IGP)

Most common Intra-AS routing protocols:

RIP: Routing Information Protocol

OSPF: Open Shortest Path First

IGRP: Interior Gateway Routing Protocol (Cisco proprietary)

Intra-AS Routing

Network Layer 4-68

Distance vector algorithm Distributed Bellman-Ford algorithm Distance metric: # of hops (max = 15 hops) Distance vectors: exchanged among

neighbors every 30 sec via Response Message (also called advertisement)

Each advertisement: list of up to 25 destination nets within AS

Included in BSD-UNIX Distribution in 1982

RIP ( Routing Information Protocol)

Network Layer

A B C

E D

From B to C: [(A,1);(B,0);(C,1);(D,1);(E,2)]

From

D to

C: [(

A,2);(B

,1);(C

,1);(D

,0);(E

,1)]

destination Next hop Interface Distance

A B BC 2B direct BC 1D direct CD 1E D CD 2

Principle RIP

Network Layer

Simple protocol, easy to implement Often used, even today Slow convergence Acceptable for small networks or

networks with a simple topology Some routing anomalies that cause very

slow convergence: like counting to infinity (see next slide)

General Characteristics RIP

Network Layer

RIP Problem : Counting to Infinity

R1 R2 R3

R2/R1R/1R3/R1R/2

R1/R2L/1R3/R2R/1

R1R R2R R3LR2L

R1/R3L/2R2/R3L/1

R3/R2R/1R1/R2R/3R3/R2R/1R1/R2R/5R3/R2R/1

R1/R3L/4R2/R3L/1[(R2,0);(R3,1)][(R1,2);(R2,1);(R3,0)]

router/interface/distance

[(R1,3);(R2,0);(R3,1)][(R1,4);(R2,1);(R3,0)]

Due to “counting to infinity” problem :Maximum distance limited to 16BUT : current large networks canhave more than 16 hops ! ==> only for small networks (16 hops = “infinity”)

Every 30 sec : advertisementAfter 180 sec of no adv.: link down

Network Layer 4-72

RIP routing tables managed by application-level process called route-d (daemon)

advertisements sent in UDP packets, periodically repeated

physical

link

network forwarding (IP) table

Transprt (UDP)

routed

physical

link

network (IP)

Transprt (UDP)

routed

forwardingtable

RIP Table processing

Network Layer

Link-State Routing Protocol : OSPF Each router obtains an overview of the

network topology in a link state database (exchange of link-state (LS) packets)

From this topology (link state database) each node calculates the shortest path (Dijkstra) to all destinations

From the shortest path the next hop is known to reach a certain destination

This next hop is used to build the routing table

OSPF : Open Shortest Path First “open”: publicly available OSPF advertisement carries one entry per neighbor router Advertisements disseminated to entire AS (via flooding)

Carried in OSPF messages directly over IP (rather than TCP or UDP)

Network Layer

Compose link-state packets

Flood the link-state packets

A B C

E D

[(BC,1),(BD,1),(AB,1)]Use sequence numbers

Same source router and same sequence number ==> discardSame source router and older sequence number ==> discard

Link-State Packets

Network Layer

Link-State Routing Protocol Overview

A B C

E D

[AB,BD,BC]

[BD,CD,DE]

[AE,DE]

[AB,AE]

incominglink statepackets

Router C : Link-State Database

Link Cost From AB 1 A AE 1 A BD 1 B BC 1 B CD 1 D DE 1 D

knowledge ofnetwork topology

Dijkstra : shortest paths

Router C : Routing Table

Dest. Nexthop

Interface

A B BCB Direct BCD Direct CDE D CD

Network Layer 4-76

Security: all OSPF messages authenticated (to prevent malicious intrusion)

Multiple same-cost paths allowed (only one path in RIP)

For each link, multiple cost metrics for different TOS (e.g., satellite link cost set “low” for best effort; high for real time)

Integrated uni- and multicast support: Multicast OSPF (MOSPF) uses same topology

data base as OSPF Hierarchical OSPF in large domains.

OSPF “advanced” features (not in RIP)

Network Layer 4-77

BACKBONE

AREA 1AREA 2

AREA 3

Hierarchical OSPF

10.10.3.0/24

10.10.2.0/24

10.10.6.0/24

10.20.15.0/24

10.25.11.0/24

[(10.10.0.0/16,3)] [(10.25.11.0/24,3);(10.20.15.0/24,3)]

internalrouters

areaborderrouters

backbonerouters

(AS) boundaryrouter

Backbone = AREA 0Between areas : always via backbone (“tree”)One border router may serve multiple areasOne area may use multiple border routers

aggregation possibleNO aggregation possible

Network Layer 4-78

Two-level hierarchy: local area, backbone. Link-state advertisements only in area each nodes has detailed area topology; only know

direction (shortest path) to nets in other areas. Internal Routers Area border routers: “summarize” distances to

nets in own area, advertise to other Area Border routers.

Backbone routers: run OSPF routing limited to backbone.

Boundary routers: connect to other AS’s.

Hierarchical OSPF

Network Layer 4-79

Chapter 4 outline4.1 Introduction and Network Service Models4.2 Routing Principles4.3 Hierarchical Routing4.4 The Internet (IP) Protocol

4.5 Routing in the Internet 4.5.1 Intra-AS routing: RIP and

OSPF 4.5.2 Inter-AS routing: BGP

4.6 What’s Inside a Router?4.7 IPv64.8 Multicast Routing4.9 Mobility

Network Layer 4-80

Internet inter-AS routing: BGPAutonomous System(has AS Number)

Stub AS

Multi connected AS (but no transit allowed)

BGP

OSPF

OSPF

RIP

RIP

OSPF

BGP

BGP

BGPBGP

Alternative : Use of default route(no BGP required)

AS Belnet = multiple domains(e.g. UGent, KULeuven, VUB, …)

peer

s

Network Layer 4-81

I-BGP and E-BGP

E-BGPE-BGP

E-BGP

E-BGPE-BGP

I-BGP

I-BGP

I-BGP : used to distributeBGP information between Border gateways from single AS

only edge routers involved in BGP

Network Layer 4-82

BGP : Example

12

54

88

Stub AS : in general no AS number

157.193/16146.123/16201.132.15/24

12/8133.12/16201.12.12/24

77/8132.2/16

AS 54

12/8

133.12/16

201.12.12/24

AS 88

157.193/16

146.123/16

201.132.15/24

NLRI : Network Layer Reachability Information

AS 54, 88

157.193/16

146.123/16

201.132.15/24

E-BGPI-BGP

AS numbers : 1-65535(65412-65535 : private)Example : Belnet : 2611

Network Layer 4-83

BGP4 (Border Gateway Protocol): the de facto standard

Path Vector protocol: similar to Distance Vector protocol each Border Gateway broadcasts to neighbors

(peers) entire path (i.e., sequence of AS’s) to destination (more general : NLRI information)

BGP announces routes to networks (CIDR enabled!), not individual hosts

Internet inter-AS routing: BGP

Network Layer 4-84

What does a BGP router do? Receiving and filtering route advertisements

from directly attached neighbor(s). Sending route advertisements to neighbors Route selection.

To route to destination X, which path (of several advertised) will be taken?

Filling routing table complex : based on AS_path, weight attribute, local preference attribute, …

BGP operation

Network Layer 4-85

Suppose: gateway X send its path to peer gateway W

W may or may not select path offered by X cost, policy (don’t route via competitors AS),

loop prevention reasons.

If W selects path advertised by X, then:Path (W,Z) = W, Path (X,Z)

Note: X can control incoming traffic by controlling its route advertisements to peers: e.g., don’t want to route traffic to Z -> don’t

advertise any routes to Z

BGP operation

Network Layer 4-86

BGP messages exchanged using TCP. BGP messages:

OPEN: opens TCP connection to peer and authenticates sender

UPDATE: advertises new path (or withdraws old)

KEEPALIVE keeps connection alive in absence of UPDATES; also ACKs OPEN request

NOTIFICATION: reports errors in previous msg; also used to close connection

BGP messages

Network Layer 4-87

Policy based routing : example 1

12/8133.12/16201.12.12/24

12

54

88

AS 54

12/8

133.12/16

201.12.12/24

AS 88 : Dual homed but no transit do not forward info from AS 54

Network Layer 4-88

Policy based routing : example 2

12/8133.12/16201.12.12/24

12

54

88

AS 54

12/8

133.12/16

201.12.12/24 AS 54 transit but only when paid

do not forward AS 12 AS 134

AS 54, 12

77/8

132.2/16

77/8132.2/16

AS 54, 12

77/8

132.2/16

AS 54

12/8

133.12/16

201.12.12/24

134

Network Layer 4-89

BGP in practice: BNIX peering point

Belnet : - support of research/education networks- support of BNIX

BNIX : Belgian National Internet eXchange- place where ISP’s can peer- connected to >40 ISP’s (see below)- peering not full mesh (see next)- other examples : AMS-IX (Nl), SFINX (Fr), LINX (UK), …

Organization BNIX MBNIX BNIX6KPN Nederland 194.53.172.71Versatel 194.53.172.115UUnet 194.53.172.78BELNET 194.53.172.65 194.53.172.254 3FFE:80B0:1000:0:2E0:F7FF:FE25:582B AT&T 194.53.172.77Arcor AG & Co 194.53.172.109Tiscali 194.53.172.97, 194.53.172.105 3FFE:80B0:1000:0:230:96FF:FEE6:DC00PSInet 194.53.172.82NETnet 194.53.172.75T-Systems 194.53.172.113Level3 194.53.172.102Easynet 194.53.172.96,194.53.172.98 3FFE:80B0:1000:0:204:DDFF:FE08:F10BT Ignite Europe 194.53.172.112X-router 194.53.172.124Skynet 194.53.172.81Perceval 194.53.172.80Opentransit 194.53.172.99 3FFE:80B0:1000:0:2D0:BBFF:FE28:7800

Network Layer 4-90

BGP : example of peering table BNIX

4: IPv4 peering 6: IPv6 peering M: Multicast peering

# ISP AS M/6 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 231 BELNET 2611 M6 M6 M6 M6 4 6 4 4 4 4 4 4 4 4 4 4 4 M 4 6 4 42 UPC/chello 6830 M6 M6 M6 M6 6 M6 6 4 4 4 4 4 4 4 4 4 4 4 M 4 M 43 Belgacom 6774 M6 M6 M6 M 6 4 4 4 4 4 4 4 M 4 4 4 4 4 4 4 4 44 Wanadoo 8277 M6 M6 M6 M 6 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 45 Easynet 4589 6 4 6 6 6 4 6 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 46 RealROOT 28747 M6 M6 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 47 ProServe B.V. 21155 6 6 6 4 4 6 4 4 4 4 4 4 4 4 4 4 4 4 4 6 4 48 Perceval 5463 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 49 Cybernet 13226 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4

10 XS4ALL Belgium 8201 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 411 Openweb 20650 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 412 AT&T 2686 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 413 Mobistar 12493 M 4 4 M 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 414 Planet Technologies 8737 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 415 Brutele 12392 M 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 416 Skynet 5432 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 417 LambdaNet 13237 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 418 EDPNet 9031 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 419 C&W Belgium 6696 M M M 4 4 4 4 4 4 4 4 4 4 4 4 4 420 Colt 8220 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 421 Tiscali 3257 6 6 M 4 4 4 6 4 4 4 4 4 4 422 HostIt 9166 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4

Not a full mesh !

Network Layer 4-91

BGP : traffic in BNIX

> 100% traffic increasein one year

Network Layer 4-92

BGP : active BGP entriesA

cti

ve B

GP

en

trie

s

Date 90 00

100.000

Trends : - increase : smaller domains used (more AS’s), more meshed, …- improved by CIDR (introduced in 1994-1995)

(information from AustralianBGP router : bgp.potaroo.net)

Network Layer 4-93

BGP : number of AS’sA

S’s

used

Date 97 03

10.000

If this continues, in a few years time no more AS numbers available switch to 32 bit addresses for AS’s (now 16 bit) ?

00

Network Layer 4-94

BGP : total address space advertised

tota

l ad

dre

ss s

pace a

dvert

ised

Date 00 03

109

Network Layer 4-95

BGP : total address space advertised (%)

tota

l ad

dre

ss s

pace a

dvert

ised

(%

)

Date 00 03

25%

About 30% of all IPv4 addresses advertised

Network Layer 4-96

Policy: Inter-AS: admin wants control over how its traffic is

routed, who routes through its net. Intra-AS: single admin, so no policy decisions

needed

Scale: hierarchical routing saves table size, reduced

update trafficPerformance: Intra-AS: can focus on performance Inter-AS: policy may dominate over performance

Why different Intra- and Inter-AS routing ?

Network Layer 4-97

Chapter 4 outline

4.1 Introduction and Network Service Models

4.2 Routing Principles4.3 Hierarchical Routing4.4 The Internet (IP) Protocol4.5 Routing in the Internet4.6 What’s Inside a Router4.7 IPv64.8 Multicast Routing4.9 Mobility

Network Layer 4-98

Table of contents 4.1 Introduction and Network Service Models 2 4.4 The Internet (IP) Protocol 7

4.4.1 IPv4 addressing 8 4.4.2 Moving a datagram from source to destination 26 4.4.3 Datagram format 40 4.4.4 IP fragmentation 42 4.4.5 ICMP: Internet Control Message Protocol 45 4.4.6 DHCP: Dynamic Host Configuration Protocol 51 4.4.7 NAT: Network Address Translation 51

4.5 Routing in the Internet 62 4.5.1 Intra-AS routing: RIP and OSPF 62 4.5.2 Inter-AS routing: BGP 79

Outline 97 Table of contents 98

Documents

Network Layer4-1 Part of slides provided by J.F Kurose and K.W. Ross, All Rights Reserved Chapter 4 Network Layer Communication Networks P. Demeester