TCP/IP Networking (2:1)

TCP/IP Networking (2:1) Joy Kuri, Haresh Dagale, T.V.Prabhakar

Grading • Evaluation • Class assignments 5% • Class tests 20% • Lab assignments 17% • Lab tests 8% • Final 50% • Lab timings • Friday: 2-00 PM to 5:00 PM

References • Textbook • “TCP/IP Illustrated” vol. 1, W.Richard Stevens • Additional reading • “Data Networks”, D.P.Bertsekas and R.W.Gallager • “Interconnections”, R.Perlman • Internet RFCs • http://www.ietf.org

Course site • drona.cedt.iisc.ernet.in/moodle • Individual accounts will be created

IP • IP addresses usually refer to interfaces, not machines • Several interfaces: several IP addresses • Same interface: multiple addresses possible

IP • Also possible to have several interfaces, but only one IP address • IP addresses are logical entities • IP provides unreliable and connectionless service • Connectionless: each datagram handled independently of others

IP addresses • 32 bit addresses in IPv4 • Divided into netid and hostid • Otherwise: too many addresses must be kept track of by routers • A form of “aggregation”: a recurrent theme hostid netid

IP addresses • Netid: allocated to organizations • Hostid: allocated by the organization • How many bits for netid and hostid? • Large corporations: many hosts, so many hostid bits required • Small organizations: few hosts, few hostid bits • Single partitioning scheme will not work

IP Addresses • Possible scheme: find out the netid-hostid partition by looking at the IP address • Requires • Breaking up the IP address space into disjoint sets • Each set has a pre-defined number of bits allocated to netid

10: Class B 1110: Class D 110: Class C Beginning with 0: Class A IP addresses IP address space

IP address classes 7 bits A: 0 hostid (24 bits) netid B: hostid (16 bits) 10 14 bits netid C: 110 21 bits hostid 8 netid multicast group id D: 1110

IP datagram Data Header

Source address Destination address IP Header

X X X X Dest addr: X Next hop: B Dest addr: X Next hop: C B A C Dest addr: X Next hop: A

TTL Source address Destination address IP Header

Other TCP UDP IP Header: Multiplexing User Entities using services of IP Kernel IP and lower layers

TTL Protocol Source address Destination address IP Header

With respect to fragmentation Identification Flags Offset TTL Protocol Source address Destination address IP Header

With respect to fragmentation In 32 bit words Hdr length ToS bits IP datagram length Version Identification Flags Offset TTL Protocol Source address Destination address IP Header

Data Data Header Header Trlr Hdr Link layer frame Link layer encapsulation

Fragmentation Datagram Frag 1 Frag 2

Fragmentation • Fragmentation and reassembly are done by the IP layer • Identification (16 bits) • To identify fragments as pieces of the original (along with source and destination addresses, and “protocol” field) • Flags (3 bits) • “More” bit • “Don’t fragment” bit • Unused • Offset (13 bits) • Offset in 8-byte units from the beginning of the payload of the original

TCP/IP Networking (2:1)