DNS: Hierarchical Name Space
root
org, net, edu, com, uk, ca
wisc, ucb, gt, cmu, mit
Client -> locak DNS Resolver -> root&edu DNS server, gatech.edu DNS Server, cc.gatech.edu DNS Server
DNS record types(partial list)
NS: name server
A: address record
MX: address in charge of handling email
DNS responses are cached
DNS negative queries are cached
Cached data periodically times out
Users/hosts trust the host-address mapping provided by DNS
DNS Packet
IP Header, UDP Header, DNS data
Query ID: 16 bit random value
