Transcript Lecture 4: Javascript Basics

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 header
Addressing
4 types
MAC – hardware address
IP – network address
domain-names – email, eg
URL’s – Web, ftp, etc services
dot-quad notation – 127.190.16.4 eg. 127.190 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