Computer Networks

1. Lab​ ​04
Name :​ ​Om​ ​Rakesh​ ​Thakkar
Roll​ ​No. :​ ​201501109
Subject :​ ​Computer​ ​Networks
Batch :​ ​1
Topic :​ ​Wireshark
Q.1)​ ​Run​ ​​nslookup​​ ​to​ ​obtain​ ​the​ ​IP​ ​address​ ​of​ ​a​ ​Web​ ​server​ ​in
Asia.
nslookup​​ ​has​ ​been​ ​performed​ ​for​ ​“​www.paytm.com​”.

2. Q.2)​ ​Run​ ​nslookup​ ​to​ ​determine​ ​the​ ​authoritative​ ​DNS​ ​servers
for​ ​a​ ​university​ ​in​ ​Europe.
nslookup​ ​​has​ ​been​ ​performed​ ​on​ ​Oxford​ ​University​ ​situated​ ​in
Europe.

3. Q.3)​ ​Run​ ​nslookup​ ​so​ ​that​ ​one​ ​of​ ​the​ ​DNS​ ​servers​ ​obtained​ ​in
Question​ ​2​ ​is​ ​queried​ ​for​ ​the​ ​mail​ ​servers​ ​for​ ​Yahoo!​ ​Mail.
Connection​ ​is​ ​timed​ ​out​ ​and​ ​no​ ​servers​ ​are​ ​reached.
Q.4)​ ​Locate​ ​the​ ​DNS​ ​query​ ​and​ ​response​ ​messages.​ ​Are​ ​they​ ​sent
over​ ​UDP​ ​or​ ​TCP?
DNS​ ​Queries​ ​and​ ​Response​ ​Messages​ ​have​ ​been​ ​located.​ ​They​ ​are
sent​ ​over​ ​UDP.
DNS​ ​Query

4. DNS​ ​Response
Q.5)​ ​What​ ​is​ ​the​ ​destination​ ​port​ ​for​ ​the​ ​DNS​ ​query​ ​message?
What​ ​is​ ​the​ ​source​ ​port​ ​of​ ​DNS​ ​response​ ​message?
The​ ​Destination​ ​Port​ ​for​ ​DNS​ ​Query​ ​is​ ​53​ ​and​ ​Source​ ​Port​ ​of​ ​DNS
Response​ ​is​ ​53.
DNS​ ​Query

5. DNS​ ​Response
Q.6)​ ​To​ ​what​ ​IP​ ​address​ ​is​ ​the​ ​DNS​ ​query​ ​message​ ​sent?​ ​Use
ipconfig​ ​to​ ​determine​ ​the​ ​IP​ ​address​ ​of​ ​your​ ​local​ ​DNS​ ​server.
Are​ ​these​ ​two​ ​IP​ ​addresses​ ​the​ ​same?
The​ ​DNS​ ​Query​ ​message​ ​has​ ​been​ ​sent​ ​to​ ​208.67.222.222,​ ​which​ ​is
the​ ​IP​ ​Address​ ​of​ ​one​ ​of​ ​my​ ​local​ ​DNS​ ​Servers​ ​as​ ​shown​ ​in​ ​the
image.

6. Q.7)​ ​Examine​ ​the​ ​DNS​ ​query​ ​message.​ ​What​ ​“Type”​ ​of​ ​DNS
query​ ​is​ ​it?​ ​Does​ ​the​ ​query​ ​message​ ​contain​ ​any​ ​“answers”?
It​ ​is​ ​a​ ​​type​ ​A​​ ​Standard​ ​Query​ ​and​ ​it​ ​doesn’t​ ​contain​ ​any​ ​answers.
Q.8)​ ​Examine​ ​the​ ​DNS​ ​response​ ​message.​ ​How​ ​many​ ​“answers”
are​ ​provided?​ ​What​ ​do​ ​each​ ​of​ ​these​ ​answers​ ​contain?
There​ ​are​ ​2​ ​answers​ ​provided​ ​in​ ​the​ ​DNS​ ​Response​ ​Message.​ ​They
contain​ ​information​ ​about​ ​the​ ​Name​ ​of​ ​host,​ ​Type​ ​of​ ​address,​ ​Class,
Time​ ​to​ ​Live,​ ​Data​ ​Length,​ ​IP​ ​Address.

7. Q.9)​ ​Consider​ ​the​ ​subsequent​ ​TCP​ ​SYN​ ​packet​ ​sent​ ​by​ ​your​ ​host.
Does​ ​the​ ​destination​ ​IP​ ​address​ ​of​ ​the​ ​SYN​ ​packet​ ​correspond​ ​to
any​ ​of​ ​the​ ​IP​ ​addresses​ ​provided​ ​in​ ​the​ ​DNS​ ​response​ ​message?
The​ ​first​ ​SYN​ ​packet​ ​was​ ​sent​ ​to​ ​104.20.0.85​ ​which​ ​corresponds​ ​to
the​ ​first​ ​IP​ ​address​ ​provided​ ​in​ ​the​ ​DNS​ ​response​ ​message.
Q.10)​ ​This​ ​web​ ​page​ ​contains​ ​images.​ ​Before​ ​retrieving​ ​each
image,​ ​does​ ​your​ ​host​ ​issue​ ​new​ ​DNS​ ​queries?
No,​ ​the​ ​host​ ​issues​ ​DNS​ ​Queries​ ​after​ ​retrieving​ ​the​ ​image.

8. ● nslookup​ ​www.mit.edu
Q.11)​ ​What​ ​is​ ​the​ ​destination​ ​port​ ​for​ ​the​ ​DNS​ ​query​ ​message?
What​ ​is​ ​the​ ​source​ ​port​ ​of​ ​DNS​ ​response​ ​message?
Destination​ ​port​ ​of​ ​DNS​ ​Query​ ​message​ ​is​ ​53​ ​and​ ​Source​ ​Port​ ​of
DNS​ ​Response​ ​message​ ​is​ ​53.
DNS​ ​Query

9. DNS​ ​Response
Q.12)​ ​To​ ​what​ ​IP​ ​address​ ​is​ ​the​ ​DNS​ ​query​ ​message​ ​sent?​ ​Is​ ​this
the​ ​IP​ ​address​ ​of​ ​your​ ​default​ ​local​ ​DNS​ ​server?
It’s​ ​sent​ ​to​ ​208.67.222.222​ ​which​ ​is​ ​the​ ​IP​ ​Address​ ​of​ ​one​ ​of​ ​my​ ​local
DNS​ ​Servers​ ​as​ ​shown​ ​in​ ​the​ ​image.
Q.13)​ ​Examine​ ​the​ ​DNS​ ​query​ ​message.​ ​What​ ​“Type”​ ​of​ ​DNS
query​ ​is​ ​it?​ ​Does​ ​the​ ​query​ ​message​ ​contain​ ​any​ ​“answers”?
The​ ​Query​ ​is​ ​​Type​ ​A​ ​​and​ ​the​ ​query​ ​message​ ​contains​ ​no​ ​answers.

10. Q.14)​ ​Examine​ ​the​ ​DNS​ ​response​ ​message.​ ​How​ ​many​ ​“answers”
are​ ​provided?​ ​What​ ​do​ ​each​ ​of​ ​these​ ​answers​ ​contain?
The​ ​DNS​ ​Response​ ​message​ ​contains​ ​3​ ​answers​ ​as​ ​shown​ ​below.​ ​It
contains​ ​Name​ ​of​ ​host,​ ​type​ ​of​ ​address,​ ​Class,​ ​TTL,​ ​Data​ ​Length​ ​and
CName.

11. ● nslookup​ ​–type=NS​ ​mit.edu
Q.16)​ ​To​ ​what​ ​IP​ ​address​ ​is​ ​the​ ​DNS​ ​query​ ​message​ ​sent?​ ​Is​ ​this
the​ ​IP​ ​address​ ​of​ ​your​ ​default​ ​local​ ​DNS​ ​server?
It​ ​is​ ​sent​ ​to​ ​208.67.222.222​ ​which​ ​is​ ​one​ ​of​ ​my​ ​local​ ​DNS​ ​Servers.
Q.17)​ ​Examine​ ​the​ ​DNS​ ​query​ ​message.​ ​What​ ​“Type”​ ​of​ ​DNS
query​ ​is​ ​it?​ ​Does​ ​the​ ​query​ ​message​ ​contain​ ​any​ ​“answers”?
It​ ​is​ ​​NS​ ​Type​ ​​DNS​ ​Query​ ​Message​ ​and​ ​contains​ ​no​ ​answers.

12. Q.18)​ ​Examine​ ​the​ ​DNS​ ​response​ ​message.​ ​What​ ​MIT
nameservers​ ​does​ ​the​ ​response​ ​message​ ​provide?​ ​Does​ ​this
response​ ​message​ ​also​ ​provide​ ​the​ ​IP​ ​addresses​ ​of​ ​the​ ​MIT
nameservers?
The​ ​nameservers​ ​are​ ​usw2,​ ​ns1-173,​ ​ns1-37,​ ​asia1,​ ​use2,​ ​use5,​ ​eur5,
asia2.​ ​We​ ​can​ ​find​ ​their​ ​IP​ ​addresses​ ​if​ ​we​ ​expand​ ​the​ ​Additional
records​ ​field​ ​in​ ​Ethereal​ ​as​ ​shown​ ​in​ ​the​ ​image​ ​below.

13. ● nslookup​ ​www.aiit.or.kr​ ​bitsy.mit.edu
Q.20)​ ​To​ ​what​ ​IP​ ​address​ ​is​ ​the​ ​DNS​ ​query​ ​message​ ​sent?​ ​Is​ ​this
the​ ​IP​ ​address​ ​of​ ​your​ ​default​ ​local​ ​DNS​ ​server?​ ​If​ ​not,​ ​what​ ​does
the​ ​IP​ ​address​ ​correspond​ ​to?
The​ ​DNS​ ​Query​ ​is​ ​sent​ ​to​ ​18.72.0.3​ ​which​ ​corresponds​ ​to
bitsy.mit.edu.

14. Q.21)​ ​Examine​ ​the​ ​DNS​ ​query​ ​message.​ ​What​ ​“Type”​ ​of​ ​DNS
query​ ​is​ ​it?​ ​Does​ ​the​ ​query​ ​message​ ​contain​ ​any​ ​“answers”?
It​ ​is​ ​a​ ​standard​ ​​Type​ ​A​ ​​DNS​ ​Query​ ​and​ ​contains​ ​no​ ​answers.
Q.22)​ ​Examine​ ​the​ ​DNS​ ​response​ ​message.​ ​How​ ​many​ ​“answers”
are​ ​provided?​ ​What​ ​does​ ​each​ ​of​ ​these​ ​answers​ ​contain?
The​ ​DNS​ ​Response​ ​message​ ​contains​ ​one​ ​answer​ ​as​ ​follows​ ​: