DNS and TCP Sequence Numbers Again EE 122

DNS and TCP Sequence Numbers (Again!) EE 122 Discussion 10/24/2011

DNS Record Types • DNS deals in terms of “resource records” • • Type A : <hostname, IP> Type NS : <domain, hostname of auth. server> Type CNAME : <canonical name, alias> TYPE MX : <name, mail-server>

DNS Packet Format Query/Response ID Flags #Questions #Answer RRs #Authority RRs #Additional RRs Questions Answers Authority Additional Records

Q 2 – Default Server to root ID = 25000 Flags (AA=0) #Questions = 1 #Answer RRs = 0 #Authority RRs = 0 #Additional RRs = 0 Q: What is A record for google. com? Ans: -Auth: -Add: --

Q 2 – Root server’s reply ID = 25000 Flags (AA=0) #Questions = 1 #Answer RRs = 0 #Authority RRs = 2 #Additional RRs = 2 Q: What is A record for google. com? Ans: -Auth: COM. IN NS A-tld-server. com 1 dy COM. IN NS B-tld-server. com 1 dy Glue Records Add: A-tld-server. com. A 10. 16. 42. 33 B-tld-server. com. A 22. 96. 81. 21

Q 2 – Default Server to. com TLD ID = 25001 Flags (AA=0) #Questions = 1 #Answer RRs = 0 #Authority RRs = 0 #Additional RRs = 0 Q: What is A record for google. com? Ans: -Auth: -Add: --

Q 2 –. com TLD to default server ID = 25001 Flags (AA=0) #Questions = 1 #Answer RRs = 0 #Authority RRs = 1 #Additional RRs = 1 Q: What is A record for google. com? Ans: -Auth: google. com NS auth. google. com Add: auth. google. com A 202. 31. 21. 42

Q 2 – Default server to Auth. Server ID = 25002 Flags (AA=0) #Questions = 1 #Answer RRs = 0 #Authority RRs = 0 #Additional RRs = 0 Q: What is A record for www. google. com? Ans: -Auth: -Add: --

Q 2 – Auth. Server to Default server ID = 25002 Flags (AA=1) #Questions = 1 #Answer RRs = 1 #Authority RRs = 0 #Additional RRs = 0 Q: What is A record for www. google. com? Ans: google. com A 202. 34. 101. 62 Auth: -Add: --

TCP Sequence Numbers • Initial sequence number for the connection is not zero • Sequence number refers to the first byte in the TCP packet payload

Question 3 a. 10001 b. 15000 c. 1501 d. 1501 – 1550