DNS and TCP Sequence Numbers (Again!) EE122 Discussion 10/24/2011

DNS Record Types DNS deals in terms of “resource records” Type A : Type NS : Type CNAME : TYPE MX :

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

Q2 – Default Server to root ID = 25000Flags (AA=0) #Questions = 1#Answer RRs = 0 #Authority RRs = 0#Additional RRs = 0 Q: What is A record for google.com? Ans: -- Auth: -- Add: --

Q2 – Root server’s reply ID = 25000Flags (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 NSA-tld-server.com 1dy COM. IN NSB-tld-server.com 1dy Add: A-tld-server.com. A B-tld-server.com. A Glue Records

Q2 – Default Server to.com TLD ID = 25001Flags (AA=0) #Questions = 1#Answer RRs = 0 #Authority RRs = 0#Additional RRs = 0 Q: What is A record for google.com? Ans: -- Auth: -- Add: --

Q2 –.com TLD to default server ID = 25001Flags (AA=0) #Questions = 1#Answer RRs = 0 #Authority RRs = 1#Additional RRs = 1 Q: What is A record for google.com? Ans: -- Auth: google.comNSauth.google.com Add: auth.google.com A

Q2 – Default server to Auth. Server ID = 25002Flags (AA=0) #Questions = 1#Answer RRs = 0 #Authority RRs = 0#Additional RRs = 0 Q: What is A record for Ans: -- Auth:-- Add: --

Q2 – Auth. Server to Default server ID = 25002Flags (AA=1) #Questions = 1#Answer RRs = 1 #Authority RRs = 0#Additional RRs = 0 Q: What is A record for Ans: google.com A 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 b c.1501 d.1501 – 1550