TCP/IP Networking TCP/IP Networking (2:1)(2:1)

Joy Kuri, Haresh Dagale, Joy Kuri, Haresh Dagale, T.V.PrabhakarT.V.Prabhakar

GradingGrading

EvaluationEvaluation– Class assignmentsClass assignments 5%5%– Class testsClass tests 20%20%– Lab assignmentsLab assignments 17%17%– Lab testsLab tests 8% 8%– FinalFinal 50%50%

Lab timingsLab timings– Friday: 2-00 PM to 5:00 PMFriday: 2-00 PM to 5:00 PM

ReferencesReferences TextbookTextbook

– ““TCP/IP Illustrated” vol. 1, TCP/IP Illustrated” vol. 1, W.Richard W.Richard StevensStevens

Additional readingAdditional reading– ““Data Networks”, Data Networks”, D.P.Bertsekas D.P.Bertsekas and and

R.W.GallagerR.W.Gallager– ““Interconnections”, Interconnections”, R.PerlmanR.Perlman

Internet RFCsInternet RFCs– http://www.ietf.orghttp://www.ietf.org

Course siteCourse site

drona.cedt.iisc.ernet.in/moodledrona.cedt.iisc.ernet.in/moodle– Individual accounts will be createdIndividual accounts will be created

IPIP IP addresses usually refer to IP addresses usually refer to

interfacesinterfaces, not machines, not machines– Several interfaces: several IP addressesSeveral interfaces: several IP addresses– Same interface: multiple addresses Same interface: multiple addresses

possiblepossible

IPIP

Also possible to have several Also possible to have several interfaces, but only one IP addressinterfaces, but only one IP address

IP addresses are logical entitiesIP addresses are logical entities IP provides unreliable and IP provides unreliable and

connectionless serviceconnectionless service– Connectionless: each datagram handled Connectionless: each datagram handled

independently of othersindependently of others

IP addressesIP addresses

32 bit addresses in IPv432 bit addresses in IPv4 Divided into netid and hostidDivided into netid and hostid

– Otherwise: too many addresses must be Otherwise: too many addresses must be kept track of by routerskept track of by routers

– A form of “aggregation”: a recurrent A form of “aggregation”: a recurrent themetheme

netid hostid

IP addressesIP addresses

Netid: allocated to organizationsNetid: allocated to organizations Hostid: allocated by the organizationHostid: allocated by the organization

How many bits for netid and hostid?How many bits for netid and hostid?– Large corporations: many hosts, so many Large corporations: many hosts, so many

hostid bits requiredhostid bits required– Small organizations: few hosts, few hostid bitsSmall organizations: few hosts, few hostid bits

Single partitioning scheme will not workSingle partitioning scheme will not work

IP AddressesIP Addresses

Possible scheme: find out the netid-Possible scheme: find out the netid-hostid partition by looking at the IP hostid partition by looking at the IP addressaddress

RequiresRequires– Breaking up the IP address space into Breaking up the IP address space into

disjoint setsdisjoint sets– Each set has a pre-defined number of Each set has a pre-defined number of

bits allocated to netidbits allocated to netid

IP addressesIP addresses

IP address space

Beginning with 0: Class A 10: Class B 110:ClassC

1110:ClassD

IP address classesIP address classes

0 hostid (24 bits)

10 14 bits hostid (16 bits)

110 21 bits

1110 multicast group id

A:

B:

C:

D:

7 bits

hostid

8

netid

netid

netid

IP datagramIP datagram

Header Data

IP HeaderIP Header

Destination address

Source address

A B

C

Dest addr: XNext hop: B

Dest addr: XNext hop: C

Dest addr: XNext hop: A

XX

XX

IP HeaderIP Header

Destination address

Source address

TTL

IP Header: MultiplexingIP Header: Multiplexing

IP and lower layersKernel

User

Entities using services of IP

TCP OtherUDP

IP HeaderIP Header

Destination address

Source address

TTL Protocol

IP HeaderIP Header

Destination address

Source address

TTL Protocol

Identification Flags Offset

With respect to fragmentation

IP HeaderIP Header

Destination address

Source address

TTL Protocol

Identification Flags Offset

With respect to fragmentation

VersionHdrlength

In 32 bit words

ToS bits IP datagram length

Link layer encapsulationLink layer encapsulation

Header Data

Header DataHdr Trlr

Link layer frame

FragmentationFragmentation

Datagram

Frag 1

Frag 2

FragmentationFragmentation Fragmentation and reassembly are done by Fragmentation and reassembly are done by

the IP layerthe IP layer Identification (16 bits) Identification (16 bits)

– To identify fragments as pieces of the original To identify fragments as pieces of the original (along with source and destination addresses, (along with source and destination addresses, and “protocol” field)and “protocol” field)

Flags (3 bits)Flags (3 bits)– ““More” bitMore” bit– ““Don’t fragment” bitDon’t fragment” bit– UnusedUnused

Offset (13 bits)Offset (13 bits)– Offset in 8-byte units from the beginning of the Offset in 8-byte units from the beginning of the

payload of the originalpayload of the original