Lecture 5: TCP/IP OSI layers 3 (IP) and 4 (TCP/UDP) IPv4 – addresses and routing, “best-effort” service Ethernet, Appletalk, etc wrap IP packets with their own protocols – used for LAN addressing. IP header – at least 20 bytes used as follows.... IP headerIP header

Addressing 4 types MAC – hardware address IP – network address domain-names – , eg URL’s – Web, ftp, etc services dot-quad notation – eg is network, 16.4 is host Class A – first network bit is 0, 8 bits long for network, 24 bits for host so 2^24 possible hosts in the network Class B – first two network bits are 10, 16 bit host address so 2^16 hosts Class C – begin with 110, 24 bit network address, 8 bit host so 256 hosts. Class D – 1110 multicast Class E – 1111 future use

Subnets, etc Subnet mask consists of n 1’s followed by 32-n 0’s Router ANDs subnet mask with host IP address to decide if the address is local or not. Classless interdomain routing (CIDR) allows for variable length 1’s in the subnet masks Dynamic Host Configuration Protocol (DHCP) Domain Name Services – translate names into IP addresses

Fragmentation/Reassembly, Routing TCP decomposes a message into segments with numbering based on last byte’s number with the message IP decomposes segments into packets with offsets Routing algorithms – Bellman-Ford or Dijkstra Border Gateway Protocols and Autonomous Systems....internet hierarchy Multicast IP (MBone), Mobile IP IPv6

TCP and UDP UDP – User Datagram Protocol Connectionless, error detection (no retransmission), no guarantees on delivery or duplication. TCP – Transport Control Protocol Connection-based, reliable, flow control. Go back n protocol for error detection and retransmission Six flags in a TCP header – URG, ACK, PSH, RST, SYN, FIN

Steps to create a TCP connection 1.A sends SYN to B – “I want to open a connection” 2.B sends SYN.ack back to A – “Okay, use this initial sequence number” 3.A sends first data packet to B – “I accept and here is the first data packet” 4.A sends packets to B and B sends AC’s back to A. 5.When one host wants to terminte, it sends a FIN and the other responds with a FIN.ack SYN Flood attacks, etc... Applications layers – FTP, SMTP, rlogin, TFTP, HTTP