McMaster University

SFWR ENG 4C03

COMPUTER NETWORK: •two or more connected computers INTERNET PROTOCOL ARCHITECTURE: •TCP/IP protocol suite: the basis for the Internet network •rules that govern transmission of information btw two points •Four layers: •Application: telnet, ftp, SMTP, HTTP, DNS •support network applications •Transport: TCP, UDP •process-process data transfer •Network: IP, ICMP, IGMP (routing protocols) •routing of datagrams from source to destination •Data Link Layer: FDDI, ATM, Ethernet, WiFi •data transfer between neighbouring network elements •Computers (hosts) implement all four •Routers (gateways) only have the bottom two NETWORK LAYER: INTERNET ROUTING: •the internet consists of a series of independently operated networks (autonomous systems, AS) •internet traffic traverses through multiple ASes •all routers must run both intra/inter-domain routing protocols •routing: the process by which nodes discover where to forward traffic such that it reaches a certain desired node IP: INTERNET PROTOCOL • subnet portion assigned to ISP by ICANN, host portion by ISP •Dynamic Host Configuration Protocol (DHCP): • dynamically get address from AS server; “plug-and-play” • host broadcasts “DHCP discover message” (optional) •DHCP server responds with “DHCP offer” msg (optional) •host requests IP address: “DHCP request” •DHCP server sends addres: “DHCP ack” msg • NAT (Network Address Translation): • local network uses just one IP address • ICMP: used by hosts/routers to communicate network-level info • error reporting/unreachable host/network/etc. •ICMP msgs carried in IP datagrams •Traceroute and ICMP •source sends series of UDP segments to dest •first has TTL =1, Second has TTL=2, etc. •Unlikely port number •When nth datagram arrives to nth router: •Router discards datagram, sends to src an ICMP msg (type 11, code 0) •Message includes name of router& IP address •When ICMP message arrives, source calculates RTT •Stopping criterion •UDP segment eventually arrives at destination host •Dest. returns ICMP “dest port unreachable” packet (type 3, code 3) •When source gets this ICMP, stops. •IPv6 Changes: •header format helps speed processing/forwarding •no fragmentation/fixed-length 40 byte header •Checksum: removed to reduce processing time at each hop •Options: allowed, but outside of header, indicated by “Next