Lecture 8. IP Fundamentals

G.Bianchi, G.Neglia, V.Mancuso

Lecture 8.Lecture 8.

Internet Network Layer:Internet Network Layer:

IP FundamentalsIP Fundamentals


OutlineOutline

Layer 3 functionalitiesInternet Protocol (IP) characteristicsIP packet (first look)IP addressesRouting tables: how to useARP


Layer 3 functionalitiesLayer 3 functionalities

This layer handles the routing of the data: i.e. delivery data to the correct destinationLayer 3 functionalities are spread all over the network

in ad hoc apparatus (routers)in your PC (as routing software)


CircuitCircuit SwitchedSwitched NetworkNetwork


PacketPacket SwitchedSwitched NetworkNetwork

Router CRouter B

Router F

Router D

Internet routing

Router E

A

G


Internet Protocol (IP)Internet Protocol (IP)RFC 791 (1981)RFC 791 (1981)

Connectionlessdatagram delivery service

Best-effortUnreliable

no guarantees of reception & packet ordererror-handling algorithm: throw away packet!

Upon buffer congestionUpon error check failed


IP functions in your PCIP functions in your PCin trasmission:

Encapsulates data from transport layer into datagramsprepare header (src & dest addresses, etc)apply routing algorithmsend datagram to network interface

in reception:check validity of incoming datagramsread headerverify whether datagram is to be forwardedif datagram has reached destination, deliverpayload to higher layer protocol


IP IP datagramdatagram formatformat20 20 bytesbytes headerheader (minimum)(minimum)

0 3 7 15 31Type of Service

TOS Total Length

Options (if any)

32 bit destination IP address

Data (if any)

Version Headerlength

16 bit identification

32 bit source IP address

Time to LiveTTL Protocol

13 bit fragment offset

Header checksum

flags3 bit

Padding (0s)


IP addressIP address32 bit string

Bit-wise notationthe natural notation

dotted notation:4 x 8 bitseach 8 bit = 0:255 integerintended for humans

10010011101000110001010000001001

10010011 . 10100011 . 00010100 . 00001001

147 . 163 . 20 . 9

Dotted Notation is often misleading, as it may hide address properties


Notation conversionNotation conversionbin bin --> dotted> dotted

147.163.20.9 (www.diepa.unipa.it)

binary 128 64 32 16 8 4 2 1 decimal

10010011 1 0 0 1 0 0 1 1 128+16+2+1=147

10100011 1 0 1 0 0 0 1 1 128+32+2+1 = 163

00010100 0 0 0 1 0 1 0 0 16+4 = 20

00001001 0 0 0 0 1 0 0 1 8+1 = 9

10010011.10100011.00010100.00001001


Notation conversionNotation conversiondotted dotted --> bin> bin

131.175.21.1 (morgana.elet.polimi.it)

decimal 128 64 32 16 8 4 2 1 binary

131 1 0 0 0 0 0 1 1 128+2+1=10000011

175 1 0 1 0 1 1 1 1 128+32+8+4+2+1 = 10101111

21 0 0 0 1 0 1 0 1 16+4+1 = 00010101

1 0 0 0 0 0 0 0 1 1 = 00000001

10000011.10101111.00010101.00000001


Need for network nameNeed for network name

Host bHost a Host c Host d

Host e Host f

All other worldwidenetworksHost g

a => left, b => left,c => right, d => righte => left, f => leftg => left, ...

in 2000 100M nodes!

R1

R2




Host e Host f


R1

R2

X => left, Y => right,Z => left, W => left,...

Network X Network Y

Network W

Network Z




Host e Host f


R1

R2

X=>left, Y=>right,everything else =>R2 knows

Network X Network Y

Network W

Network Z

Where is network name?


IP Address StructureIP Address Structurepartitioned into two fieldspartitioned into two fields

Network id (or prefix)(part used for routing)

Host number(specifies device on the net)

32 bit IP address

Dotted notation: AAA.BBB.CCC.DDD - no physical meaning!A more correct notation should be: NNNNN-HHHHH


IP Address StructureIP Address Structurepartitioned into two fieldspartitioned into two fields

Network prefix: 3 Host number(specifies device on the net)

32 bit IP address

3-2 3-5 3-8

Host Addresses3-8 means: host 8 on network 3


Dotted notation Dotted notation vsvs IP address structureIP address structure

Dotted NotationAAA.BBB.CCC.DDD

no physical meaning!often misleading!

– it may hide address properties

More correct notation:NNNNN-HHHHH

Physical meaning (network prefix, host #)Prefix size is variable,Not implicit in the IP address (from 1993)

Separator must be provided externally


ExampleExampleIP address 147.163.22.130

Bitwise notation:

Network prefix:Externally providedExample: first 22 bits network ID, last 10 bits host ID

Network prefix notation:/22 (modern notation)Netmask (traditional notation)

Netmask dotted decimal: 255.255.252.0

10010011.10100011.00010110.10000010

11111111.11111111.11111100.00000000

10010011.10100011.00010110.10000010


Network AddressNetwork Address

Local Host Interface:147.163.21.9/22 10010011.10100011.00010101.00001001

147.163.21.9

Network Address 10010011.10100011.00010100.00000000

Network prefix Hostid

Dotted notation for the network address147.163.20.0

Pure Convenience (not only for men)!


Naming in IP: networksNaming in IP: networks

Network 143

Host 2Host 1

Network 542

Host 12 Host 2

Network xxx

Network yyy All other worldwidenetworks

Network name: Network prefix 00000000000000

Special IP addresses, with all 0’s in host partAll existing (physical) networks have different names!


Naming in Naming in IPIP: hosts: hosts

Worldwide Unique Network address AssignmentWithin a network, unique IP address assignment to each host (better: interface)

CONCLUSION: ALL EXISTING HOSTS HAVE DIFFERENT IP ADDRESSES

3-2 3-5 3-8

Host Addresses3-8 means: host 8 on network 3Network address: 3-0

Host-id field set to 0 means this addressis a name for an entire network(this is network 3, unique name in all the world)

Netid3

Hostid0


IP address 147.163.22.130

Network prefix:/22 (equivalently: 255.255.252.0)

It is an IP address for a HOSTSimple: not all 0’s in host part

Which belongs to network 147.163.20.0/22Simple: just set 0’s in host part

ExampleExample

10010011.10100011.00010110.10000010

10010011.10100011.00010110.10000010

10010011.10100011.00010100.00000000


Naming in Naming in IPIP: broadcast: broadcast

3-2 3-5 3-8

Netaddr3

HostidAll 1’s Means: all the hosts on the considered network!

Used to send a “broadcast” information (to all the Attached hosts)

Example: network 147.163.20.0/22What is the IP address to use for broadcasting?Simple: just set all 1’s in host part

Broadcast address: 147.163.23.255

10010011.10100011.00010111.11111111


TestTest

147.163.0.128 (prefix: /26)Network? Host? Broadcast?




Think in binary! And everything becomes trivial….


Second role of an IP address: routingSecond role of an IP address: routingRouting = ability to forward packets to destinationRouting = ability to forward packets to destination

Network 143

143-1

Host 2Host 1

143-2143-3

542-1

Network 542

Host 12

542-3

Host 2

542-2

Routing: based on network addresses

Key idea: first find the physical network where the host resides, and then find specific host routing tables addressing each of 100M+ hosts would be unfeasible

A Router (2nd definition): computer with 2+ interfaces

Connects different networks (hence the name inter-net), eventually with different technologiesAn IP address per each interfaceTask: collect datagrams on one interface and forward on other(s)


PacketPacket RoutingRouting (at (at locallocal hosthost))

Application running at local computergenerates a datagram destined toIP address 321-2 [host 2 on network 321]

Local host operation:Knows its IP address NNN-XXXThus knows on which network NNN the computer is attachedHence, knows whether packet 321-2 needs to be forwarded to

A. an host on this same networkB. an host on a different network

321-2

Local host runs IP routing SW(some people thinksRouting sw confined At routers…)


NetAddressNetAddress computation (Masking)computation (Masking)

Is on the same network?

Local Host Interface:147.163.21.9

Destination IPaddr:147.163.22.130 10010011.10100011.00010110.10000010

147.163.22.130

147.163.21.9

10010011.10100011.00010101.00001001

Netaddresses are equal!

They are on the same network!

How does IP software really work?


NetAddressNetAddress computation (Masking)computation (Masking)Network mask

associated to the network addressstring of 1s in network address, 0s in host address

Local Host Interface:147.163.21.9 10010011.10100011.00010101.00001001

147.163.21.9

Netmask 11111111.11111111.11111100.00000000

Netaddress Hostid

Dotted notation for the netmask255.255.252.0


NetAddressNetAddress computation (Masking)computation (Masking)

Is on the same network?

Destination IPaddr:147.163.22.130 10010011.10100011.00010110.10000010

147.163.22.130

147.163.21.9255.255.252.0

Netmask:255.255.252.0 11111111.11111111.11111100.00000000

Bitwise AND

10010011.10100011.00010100.00000000Network Address:147.163.20.0

=?

=10010011.10100011.00010100.00000000

=

They are on the same network!


Inside the LANInside the LAN

43-543-3

• Router not involved43-1

Who is IP 43-1?

43-1ff:ff:ff:ff:ff:ff

43-0 = 43-0 (it is on this net)

Physical transmission: a) resolve IP address in physical network address, b) encapsulate packet in datalink frame, and c) deliver according to local networking technology

43-1


Host configuration (Windows)Host configuration (Windows)


Possible Possible netmasknetmask valuesvalues““magic magic netmasknetmask numbersnumbers””

1 1 1 1 1 1 1 1 = 2551 1 1 1 1 1 1 0 = 2541 1 1 1 1 1 0 0 = 2521 1 1 1 1 0 0 0 = 2481 1 1 1 0 0 0 0 = 2401 1 1 0 0 0 0 0 = 2241 1 0 0 0 0 0 0 = 1921 0 0 0 0 0 0 0 = 128128 64 32 16 8 4 2 1

Examples: /21 255.255.248.0/29 255.255.255.248


GoingGoing through a through a RouterRouter

43-143-3

• At least one router on the network• Local router IP interface: destination for all packets

addressed outside the local physical network

321-2

Who is IP 43-3? MAC ff:04.a

321-2ff:04.a

321-0 != 43-0 (not on this net!)Send to 43-3: he knows more…

Physical transmission: a) resolve IP address in physical network address, b) encapsulate packet in datalink frame, and c) deliver according to local networking technology

43-5


Network 321

321-12 321-2

Network 4343-1

321-2Net 321?? Not this net!Go to host 43-3

43-3 321-2Net 321?? Yes, I’m attached to!translate 321-1 in phynet address & deliver

Network 175175-1 175-2

RouterRouter operationoperation::Direct Direct ForwardingForwarding


Network 175 Network 321175-1 175-2

321-12 321-2

Network 4343-1

175-2Net 175?? Not this net!Go to host 43-3

151-6

175-2Net 175?? Not here.But my tables say thatrouter 151.4 knows.Go there (with 151 nettechnology)

43-3

151-4Network 151

INTERNET = arbitrary networks interconnected via routers

RouterRouter operationoperation::IndirectIndirect ForwardingForwarding


Layered viewLayered view

IP

N.i. 1

application

transport

IPnetwork

interface 3

Logicalnetwork14000-0

application

transport

IPnetworkinterface

Host B 29999-6

N.i. 2

IP

N.i. 2 N.i.3

dest. addr. 29999-6Host A 14000-4

RouterIndirect

forwarding

RouterDirect

forwarding

Logicalnetwork29999-0

Logicalnetwork111-0

Datagrams travel from router to router (indirect forwarding)until a router is on the same network of dest host (direct forwarding)


Inter Inter -- Net exampleNet example

Ethernet

IP

TCP UDP

ATM PPP FDDI

IP

FDDI

IP

TCP UDP

AtmEthernet ATM

IP

ATMswitch

hosthost

PPP

IP

ATM networkEthernetTelephone

line

FDDI

router router router... ... ... ... ... ... ... ...

1 hop = ATM network andswitch crossing!


Internet Internet vsvs specificspecificphysicalphysical networkingnetworking technologytechnologyIP: an overlay networking protocol

interconnection of widely heterogeneous networksseen by TCP/IP as sub networksRouters do not care about specific network technology (LAN, WAN,circuit switching, packet switching, …) but they NEED to have a specific network interface (Routers with Ethernet interfaces cheap; with FDDI or ATM very expensive…)

Router duties: just select destination (end or intermediate router)!then map IPaddr in physical network addressIP datagrams tunneled into underlying network data unitsspecific physical network routing may be extremely complex (router sees this as single hop)


Routing tableRouting table20000-5 20000-6 30000-12 30000-7

Net20000

Net30000R1 R2 R3

10000-32

Net10000

Other nets

Net 50000

40000-8

Destination Network Next Hop20000 Direct forward30000 Direct forward10000 20000-540000 30000-750000 30000-7default 20000-5

R2 routing table

Net 40000

Three cases: 1) direct forwarding 2) Indirect forwarding (explicit) 3) Indirect forwarding via default router (when available)

Routing vianetwork Id,not host Id!

Otherwisetoo large tables


Routing table lookupRouting table lookup132.43.3.5 132.43.0.6 208.0.1.12 208.0.1.7

Net132.43.0.0

Net208.0.1.0R1 R2 R3

10.12.1.32

Net10.0.0.0

Other nets

Net 193.33.9.0

208.0.2.8

Dest net /mask Next Hop132.43.0.0 /16 Direct forward208.0.1.0 /24 Direct forward10.0.0.0 /8 132.43.3.5208.0.2.0 /24 208.0.1.7193.33.9.0 /24 208.0.1.7208.1.1.0 /24 132.43.3.5

R2 routing table

Net 208.0.2.0

208.1.1.0

default 132.43.3.5

IP dest: 208.1.1.14

For (rows in rtab)IP_dest&mask == dest_net?

Found:208.1.1.0

Lookup?goto 132.43.3.5


Route print (Route print (DOS,unixDOS,unix))shows routing table of your PCshows routing table of your PC

(remember: your PC is a simple IP router)(remember: your PC is a simple IP router)

===========================================================================Active Routes:Network Destination Netmask Gateway Interface Metric

0.0.0.0 0.0.0.0 10.163.57.1 10.163.57.77 110.163.57.0 255.255.255.0 10.163.57.77 10.163.57.77 110.163.57.77 255.255.255.255 127.0.0.1 127.0.0.1 1

10.255.255.255 255.255.255.255 10.163.57.77 10.163.57.77 1127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1224.0.0.0 224.0.0.0 10.163.57.77 10.163.57.77 1

255.255.255.255 255.255.255.255 10.163.57.77 10.163.57.77 1Default Gateway: 10.163.57.1===========================================================================


ClassfulClassful IP AddressingIP AddressingOriginally (from 1981) a rigid two-level

address structure

Network number(network prefix) Host number

32 bit IP address8,16 or 24 bits


Primary Address ClassesPrimary Address Classes3 standardized classes3 standardized classes

0 NET ID (7bit) HOST ID (24 bit)

1 NET ID (14bit) HOST ID (16 bit)0

1 NET ID (21bit) HOST ID (8 bit)1 0

Class A - /8 network prefix

Class B - /16 network prefix

Class C - /24 network prefix

/xx notation: modern notationin principle not necessary for classful IP addressing


Additional classesAdditional classes

1 Multicast Group ID (28 bit)1 1

Class D: IP multicasting0

1 reserved1 1

Class E: reserved for experimental use1


Dotted Decimal RangesDotted Decimal Ranges

Address Class

Class A

Class B

Class C

Dotted Decimal ranges

1.xxx.xxx.xxx through 126.xxx.xxx.xxx

128.0.xxx.xxx through 191.255.xxx.xxx

192.0.0.xxx through 223.255.255.xxx

Class D (mcast) 224.xxx.xxx.xxx through 239.xxx.xxx.xxx

Class E (exper) 240.xxx.xxx.xxx through 255.xxx.xxx.xxx


ExamplesExamples

15.10.10.90Net ID Host ID

CLASS A


CLASS B


CLASS C


Addressing networksAddressing networksAll 0s host ID = reserved for network name. Examples:

CLASS A network: 13.0.0.0CLASS B network: 131.175.0.0CLASS C network: 193.32.43.0

Test:188.66.32.0 = ???122.0.0.0 = ???


Special AddressesSpecial Addressesall 1s host id: broadcast address (all hosts in the network)

es. 131.175.255.255 =all hosts attached to the 131.175 net

0.0.0.0 = THIS host on THIS network (0.x.x.x also reserved)

e.g. to boot diskless WS (BOOTP)

127.x.x.x used for loopback (es. 127.0.0.1=localhost)

all 1s = 255.255.255.255 = limited broadcast all nodes on THIS local network


Address blocks for private InternetsAddress blocks for private Internets(RFC 1918)(RFC 1918)

IANAIANA--AllocatedAllocated, Non, Non--Internet Internet RoutableRoutable,,IP IP AddressAddress SchemesSchemes

Class Network Address RangeA 10.0.0.0 - 10.255.255.255 B 172.16.0.0 - 172.31.255.255 C 192.168.0.0 - 192.168.255.255

To be used by private organizations not connected to the InternetNo need to ask to IANA or InterNIC for these addresses.Use Network Address Translator (NAT) when external connectivity needed


Network Address TranslatorNetwork Address Translator“Inside” Network “Outside” Network

10.0.0.2

10.0.0.3

NAT Table

Inside LocalIP Address

GlobalIP Address

10.0.0.210.0.0.3

192.69.1.1192.69.1.2

Source Address

NAT

Internet10.0.0.2 192.69.1.1

Map external address with Internal ones (may be a subset)


Counting upCounting up32 bit IP address:

232 = 4.294.967.296 theoretical IP addressesclass A:

27-2 =126 networks [0.0.0.0 and 127.0.0.0 reserved]224-2 = 16.777.214 maximum hosts

2.113.928.964 addressable hosts (49,22% of max)class B

214=16.384 networks216-2 = 65.534 maximum hosts

1.073.709.056 addressable hosts (24,99% of max)class C

221=2.097.152 networks28-2 = 254 maximum hosts

532.676.608 addressable hosts (12,40% of max)

Class AClass B

CDE

The IPaddress

Pie!


Routing table lookupRouting table lookup132.43.3.5 132.43.0.6 208.0.1.12 208.0.1.7

Net132.43.0.0

Net208.0.1.0R1 R2 R3

10.12.1.32

Net10.0.0.0

Other nets

Net 193.33.9.0

208.0.2.8

Destination net Next Hop132.43.0.0 Direct forward208.0.1.0 Direct forward10.0.0.0 132.43.3.5208.0.2.0 208.0.1.7193.33.9.0 208.0.1.7208.1.1.0 132.43.3.5

R2 routing table

Net 208.0.2.0

208.1.1.0

default 132.43.3.5

IP dest: 208.1.1.14

Which class?C

Destination net?208.1.1.0

Lookup?goto 132.43.3.5


Net Address computation Net Address computation (Masking)(Masking)

class mask:Depends on first bits of address (which specify class)

Class A mask: 255.0.0.0 Class B mask: 255.255.0.0Class C mask: 255.255.255.0

10011111 01100100 00001001 00010010

11111111 11111111 00000000 00000000

DEST IP address:159.100.9.18

class B

Class B Mask:255.255.0.0

Bitwise AND

Net address159.100.0.0 10011111 01100100 00000000 00000000

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Lecture 8. IP Fundamentals