DNS

1
???????? DNS
???? ??? ???. ?????? ???? ????, ????
????. ??????? ???? ????? ????? ????????
????????? ?- DNS ??? client-server ??? ?????
?????? OPNET .
2
???? ???????

• ????? ???????? ?- DNS ?? ???????.
• ????? use-cases ??????????.
• ???? ?- OPNET.
• ????? ???? ?????? ????????? ?"? ?-OPNET .
• ???? ????????? (debugging ) .
• ?????.
• ????? ?????? .

3
DNS- background

• DNS- Domain Name System
• The system is used over the internet to map names
  to IP addresses and addresses to names.
• The DNS is a hierarchical name space designed in
  a tree structure with the root at the top.
• The tree can have up to 128 levels

4
DNS- background (cont).Hierarchy overview
Root
Country domains
Inverse domain
Generic domains
5
DNS- the Protocol

• The two resolution options of mapping requests
• Recursive resolution.
• The server acts as resolver querying another
  server and so on recursively, until it receives
  final answer, and sends it to client.

6
Simulation- Recursive resolusion.
Root server
if cached
if cached
10
9
4
il
3
if cached
8
com
if cached
5
11
ac.il
2
7
if cached
12
6
dns.yahoo.com
technion.ac.il
1
comnet.technion.ac.il
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DNS- the Protocol (cont.)

• Iterative resolution.
• The server repeats the same query to multiple
  servers until receives answer, which is sent back
  to the client

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Simulation- Iterative resolusion.
ac.il
com (has ac.il IP)
comnet.technion.ac.il
if cached
3
4
if cached
5
comnet.technion.ac.il
2
technion.ac.il
7
if cached
8
6
1
comnet.technion.ac.il
comnet.technion.ac.il
dns.yahoo.com
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DNS MESSAGES
DNS has two types of messagesquery and response,
both have the same format.
Header question section
Header question section Answer section Authoritati
ve section Additional section
Identical
Response
Query
10
OPNET model simulator

• ???????? ?????? ????? ??????? ????????? ??????
  ?????.
• ?????? ????? ????? ????? ??????? ????? ?"? ????
  ???? ?????? ???? ????, ?????? ?????????? ?? ??
  ??????? ??, ??? ?????? ???? ?? ??????? ?????? ??
  ?????? ?? ??????????? ??????? ?? ???? ??????
  ??????? ????.
• ????? ????? ?????? ?????????? ??????? ???? (????
  TCP/IP ) ??? ?????? ????? ?????????? ????? ?"?
  ????? ???? ???????.

11
OPNET general node model
12
Server process model
13
Server query resolve process
14
Client process model
15
Server DataBase- Resource Record example-

• netvision.net.il MX 1
  mx20.netvision.net.il
• netvision.net.il A 194.90.1.6
• netvision.net.il NS
  dns.netvision.net.il
• netvision.net.il SOA
  dns.netvision.net.il
• hostmaster.netvision.net.il (
• 2001121604 serial (version)
• 28800 refresh period (8
  hours)
• 7200 retry interval (2 hours)
• 604800 expire time (1 week)
• 86400 default ttl (1 day)
• )

16
DNS Experiment
17
Simulation topology exp.