Question on NAT

! The private network in the figure is connected to the Internet through a traditional NAPT. The router has a single public address: (131.175.21.130).

a) Can three private hosts be simultaneously connected to the same web server on the Internet?

b) 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.

10.10.10.1Port: 6678

10.10.10.2Port: 6678

10.10.10.3Port: 7348

10.10.10.254190.10.45.3

Server WEBPort: 80

Question on NAT

a) Can three private hosts be simultaneously connected to the same web server on the Internet?Yes, because NAPT can multiplex multiple private IP addresses onto the same public IP address by translating also the ports.

10.10.10.254190.10.45.3

Server WEBPort: 8010.10.10.1

Port: 6678

10.10.10.2Port: 6678

10.10.10.3Port: 7348

Question on NAT

10.10.10.254190.10.45.3

Server WEBPorta: 8010.10.10.1

Port: 6678

10.10.10.2Port: 6678

10.10.10.3Port: 7348

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

NAT Table

Question on NAT

10.10.10.254190.10.45.3

Server WEBPort: 80

10.10.10.1Port: 6678

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

IP src: 10.10.10.1IP des: 190.10.45.3Port src: 6678Port des: 80

IP src: 131.175.21.130IP des: 190.10.45.3Port src: 6678Port des: 80

NAT Table

Question on NAT

10.10.10.254190.10.45.3

Server WEBPort: 80

10.10.10.2Port: 6678

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

IP src: 10.10.10.2IP des: 190.10.45.3Port src: 6678Port des: 80

IP src: 131.175.21.130IP des: 190.10.45.3Port src: 7000Port des: 80

NAT Table

Question on NAT

10.10.10.254190.10.45.3

Server WEBPorta: 80

10.10.10.3Port: 6678

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

IP src: 10.10.10.3IP des: 190.10.45.3Port src: 7348Port des: 80

IP src: 131.175.21.130IP des: 190.10.45.3Port src: 7348Port des: 80

NAT Table

Internet

Question on Tunneling

! 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.a) Write the source and destination address of the IP packet travelling in

the Internet.

R1

10.10.11.110.10.10.3

R2

10.10.10.210.10.11.2

136.66.71.254133.32.15.254

Intranet AIntranet B

SubNet10.10.11.0/24SubNet

10.10.10.0/24

Internet

Question on Tunneling

R1

10.10.11.110.10.10.3

R2

10.10.10.210.10.11.2

136.66.71.254133.32.15.254

Intranet AIntranet B

SubNet10.10.11.0/24SubNet

10.10.10.0/24

IP_src:10.10.10.3

IP_des: 10.10.11.1

Payload

IP_src:10.10.10.3

IP_des: 10.10.11.1

Payload

IP_src:136.66.71.254

IP_des: 133.32.15.254

IP_src:10.10.10.3

IP_des: 10.10.11.1

Payload

Question HTTP (1)

! In the following you can find the content of an HTTP Request. Answer to the following questions, indicatingwhere (e.g., in which field) in the HTTP Request you can find the answer:

GET /martignon/index.html HTTP/1.1 Host: www.lri.frUser Agent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en) AppleWebKit/124 (KHTML, like Gecko) Safari/125 Accept: ext/xml, application/xml, application/xhtml+xml, text/html;q=0.9, text/plain;q=0.8, image/png,*,*;q=0.5 Accept-Language: frKeep-Alive: 300 Connection: keep-alive

Question HTTP (1)

1) What is the requested URL? 2) Which version of HTTP is used? 3) Does the browser ask for a persistent

or a non-persistent connection?4) What is, in your opinion, the utility in

indicating the type (and version) of browser used by the client in the HTTP Request?

Question HTTP (1)

1) The requested URL is (see the first two lines of the HTTP message): www.lri.fr/martignon/index.html

2) The HTTP version used is 1.1(first line of the HTTP message)

3) It’s a persistent connection (the header part concerned is connection:keep-alive ).

4) The information on the browser type is needed to “customize” the answer on the browser (e.g., if the HTTP server needs to send a “mobile” version of a website to the client, on a smartphone).

Question HTTP (2)

! An HTTP client sends the following message:Client:GET http://www.lri.fr/index.html HTTP/1.1 User-agent: Mozilla/4.0 Accept: text/html, image/gif, image/jpeg If-modified-since: 27 Feb 2017 08:10:00

a) Write down two feasible responses of the HTTP server (only the status line)

b) Assuming that the message is sent through a Proxy, specify the behavior of the Proxy itself

Question HTTP (2)

! Server Responses:

Client:GET http://www.lri.fr/index.html HTTP/1.1 User-agent: Mozilla/4.0 Accept: text/html, image/gif, image/jpeg If-modified-since: 27 Feb 2017 08:10:00

Server:

HTTP/1.1 200 OKServer:

HTTP/1.1 304 Not Modified

Question HTTP (2)

! The Proxy crosscheck if the resource isavailable 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??

Client:GET http://www.lri.fr/index.html HTTP/1.1 User-agent: Mozilla/4.0 Accept: text/html, image/gif, image/jpeg If-modified-since: 27 Feb 2017 08:10:00

Exercice HTTP! Un client HTTP demande à un serveur HTTP une page web constituée

d’un objet de base (ficher HTML) et de 10 autres objets. Chaque objet a une taille L=200 [kbit]. La liaison, bidirectionnelle, entre le client et le serveur a une capacité C=100 [kbit/s]. Les messages de contrôle utilisés pour ouvrir la connexion TCP entre client et serveur, ainsi que le message HTTP “GET” ont une taille m=100 [bit]. Le délai de propagation du lien est tau = 100 [ms].

! Calculer le temps total nécessaire pour que le client reçoive la page web et les 10 objets dans les 2 cas suivants :

a) le client HTTP ouvre en parallèle en modalité non-persistent toutes les connexions TCP nécessaires à télécharger la page web et ses objets (on fait l’hypothèse que le rythme de transmission de chaque connexion TCP soit égal à r=C/N, N est le nombre de connexions ouvertes en parallèle

b) Le client HTTP ouvre en série 11 connexions TCP en modalité non-persistent.

tau