Question on NAT
10.10.10.1
Port: 6678
Server WEB
Port: 80
190.10.45.3
10.10.10.2
Port: 6678
10.10.10.254
10.10.10.3
Port: 7348 a) b)
The private network in the figure is connected to the Internet througha traditional NAPT. The router has a single public address: (131.175.21.130).
Can three private host be simultaneoulsy connected to the same web server on the Internet?
If so, write down IP address and port addresses in the packets generated by the private hosts and directed to the web server (before and after the
NAPT router). Write down the NAT table of the router.

Question on NAT
10.10.10.1
Port: 6678
Server WEB
Port: 80
190.10.45.3
10.10.10.2
Port: 6678
10.10.10.254
10.10.10.3
Port: 7348 a) Can three private host be simultaneoulsy connected to the same web server on the Internet?
Yes, beacause NAPT can multiplex multile private IP addresses onto the same public IP address by translating also the ports.

Question on NAT
10.10.10.1
Port: 6678
Server WEB
Porta: 80
190.10.45.3
10.10.10.2
Port: 6678
10.10.10.254
10.10.10.3
Port: 7348
NAT Table
10.10.10.1, 6678 131.175.21.130, 6678
10.10.10.2, 6678 131.175.21.130, 7000
10.10.10.3, 7348 131.175.21.130, 7348

Question on NAT
IP src: 10.10.10.1
IP des: 190.10.45.3
Port src: 6678
Port des: 80
IP src: 131.175.21.130
IP des: 190.10.45.3
Port src: 6678
Port des: 80
Server WEB
Port: 80
10.10.10.1
Port: 6678
10.10.10.254
190.10.45.3
NAT Table
10.10.10.1, 6678 131.175.21.130, 6678
10.10.10.2, 6678 131.175.21.130, 7000
10.10.10.3, 7348 131.175.21.130, 7348

Question on NAT
IP src: 10.10.10.2
IP des: 190.10.45.3
Porta src: 6678
Port des: 80
IP src: 131.175.21.130
IP des: 190.10.45.3
Porta src: 7000
Port des: 80
Server WEB
Port: 80
10.10.10.2
Port: 6678
10.10.10.254
190.10.45.3
NAT Table
10.10.10.1, 6678 131.175.21.130, 6678
10.10.10.2, 6678 131.175.21.130, 7000
10.10.10.3, 7348 131.175.21.130, 7348

Question on NAT
IP src: 10.10.10.3
IP des: 190.10.45.3
Porta src: 7348
Porta des: 80
IP src: 131.175.21.130
IP des: 190.10.45.3
Porta src: 7348
Porta des: 80
Server WEB
Porta: 80
10.10.10.3
Port: 6678
10.10.10.254
190.10.45.3
NAT Table
10.10.10.1, 6678 131.175.21.130, 6678
10.10.10.2, 6678 131.175.21.130, 7000
10.10.10.3, 7348 131.175.21.130, 7348

Question on Tunneling a)
Intranet A and Intranet B are connected through a VPN.
The host 10.10.10.3 sends an IP packet to host 10.10.11.1.
Write the source and destination address of the IP packet travelling in the Internet.
136.66.71.254
R1
10.10.10.2
10.10.10.3
SubNet
10.10.10.0/24
Intranet A
Internet
SubNet
10.10.11.0/24
Intranet B
133.32.15.254
R2
10.10.11.2
10.10.11.1

Question on Tunneling
IP_src:136.66.71.254
IP_src:10.10.10.3
IP_des: 10.10.11.1
Payload
IP_des: 133.32.15.254
IP_src:10.10.10.3
IP_des: 10.10.11.1
Payload
136.66.71.254
R1
10.10.10.2
10.10.10.3
SubNet
10.10.10.0/24
Intranet A
Internet
IP_src:10.10.10.3
IP_des: 10.10.11.1
Payload
SubNet
10.10.11.0/24
Intranet B
133.32.15.254
R2
10.10.11.2
10.10.11.1

Question HTTP a)
Client :
GET http://www.polimi.it/index.html HTTP/1.0
User-agent: Mozilla/4.0
Accept: text/html, image/gif, image/jpeg
If-modified-since: 27 Jun 2001 08:10:00
Write down two feasible responses of the
HTTP server (only status line b) Assuming that the message is sent through a
Proxy, specify the behavior of the Proxy itself

Question HTTP
Client :
GET http://www.polimi.it/index.html HTTP/1.0
User-agent: Mozilla/4.0
Accept: text/html, image/gif, image/jpeg
If-modified-since: 27 Jun 2001 08:10:00
Server :
HTTP/1.1 200 OK
Server :
HTTP/1.1 304 Not Modified

Question HTTP
Client :
GET http://www.polimi.it/index.html HTTP/1.0
User-agent: Mozilla/4.0
Accept: text/html, image/gif, image/jpeg
If-modified-since: 27 Jun 2001 08:10:00
The Proxy crosscheck if the resource is available in the local cache.
If not:
Forwards the message to the server
If so, crosschecks the date associated to the resource:
If it’s older than the one specified in the message
If-modified-since, it it forwarsd the message to the server.
Otherwise??