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Figure 1 shows how an internal desktop (denoted as Proxy Client) is protected by a proxy firewall. Let's assume that the internal desktop is used by Alice and she wants to remotely log into the external machine denoted as the Telnet server. Alice runs a Telnet client program on her desktop.

https://cms.psu.edu/AngelUploads/QuestionData/bf3bab49-1e7a-4ed0-b5e8-4a21f5b971df/554quiz4f1.PNG#{005A29D3-9A39-4A67-B9CD-785966CEBFFF}

 

  1. Let’s first assume that the Proxy Firewall does not exist. In this case, when Alice needs to remotely login into the external Telnet server, the Telnet client program that runs on her desktop will send packet #1 of the TCP 3-way handshake protocol to the Telnet Server. What is the source IP address put in the header of packet #1 (4 points)?

 

  1. After a while, packet #2 of the TCP 3-way handshake protocol will be sent from the Telnet Server to the internal Proxy client. What is the source port number put in the header of packet #2 (4 points)?

 

  1. After a while, packet #3 of the TCP 3-way handshake protocol will be sent from the internal Telnet client program to the Telnet Server program. What is the dest IP address put in the header of packet #3? (4 points)

 

  1. Based on your answers to Questions 1, 2, and 3, you will notice that if the Telnet server is malicious, the Internal Network will face a major security threat. What is it? (6 points)

 

1.5: To address this security threat, let’s deploy the Proxy Firewall. To see why the proxy firewall is useful, let’s revisit the same example. When Alice needs to remotely login into the Telnet server, the Telnet client program will send packet #1 of the TCP 3-way handshake protocol to the Telnet Server.

 

  1. The destination IP address put in the header of packet #1 cannot be the IP address of the Proxy Firewall. Why? (6 points)

 

  1. What is the dest IP address put in the header of packet #1? (4 points)

 

1.6: When Packet #1 arrives at the Proxy Firewall:

 

 

  1. The Proxy Firewall will not let the packet directly go through the firewall. Why? (6 points)

 

8. When the packet leaves the Proxy Firewall, what is the source IP address in the header? (4 points)

 

  1. After a while, packet #2 of the TCP 3-way handshake protocol will be sent from the Telnet Server to the Proxy Firewall. What is the destination IP address put in the header of packet #2? (4 points)

 

  1. After a while, the Proxy Firewall will receive packet #2. Then the firewall will modify the packet a bit. When this packet leaves the Proxy Firewall, what is the source IP address in the header? (4 points)

 

 

Figure 2 shows the screened subnet firewall architecture.

https://cms.psu.edu/AngelUploads/Content/201011SPWD___IIST__554_001/_assoc/2C900A74482D47F5A462E3E248FFCD8B/554quiz4f2v2.PNG

 

  1. Let’s assume the PC next to the Email Coordinator is Alice’s desktop. Let’s assume the IP address of this desktop is 130.3.20.2. Please give a concrete packet filtering firewall rule for the Screening Router to block any outgoing TCP connection requests from Alice’s desktop to a remote machine. The format of a firewall rule is: || Rule ID || packet direction || source IP || dest IP || protocol name || source port || dest port || ACK || decision || (10 points)

 

  1. Please give a concrete filtering firewall rule for the Screening Router to allow incoming TCP packets to reach the Web server. (8 points)

 

2.3: Since the Email server in the Peripheral Network could be broken, it is risky let the internal desktops to be directly connected to the email server. To solve this problem, we will set up the Email Coordinator in the Internal Network.

 

  1. When Alice wants to send out an email. The Outlook program that runs on Alice’s desktop will compose and send out some packets. In the header of the first packet, denoted packet #1, sent out from Outlook, what is the destination IP address? (6 points)

 

  1. When packet #1 leaves the Email Coordinator, what is the source IP address of its header? (6 points)

 

  1. To make sure that the email server on the Peripheral Network can only communicate with the Email Coordinator, Firewall II needs to enforce 4 firewall rules if not less. What are they? (14 points)

 

  1. Tell three fundamental differences between packet filtering firewalls and proxy server firewalls. (10 points)
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1) Source xxxxxxx address put xxxxxxx the header xxxxxxx xxxxxxx #1 xxxxxxx be the xxxxxxx address of xxxxxxx proxy xxxxxxx xxxxxxx 5.6.7.8 that xxxxxxx inside the xxxxxxx The source xxxxxxx number put xxxxxxx the header xxxxxxx packet #2 xxxxxxx xxxxxxx The xxxxxxx IP address xxxxxxx in the xxxxxxx of xxxxxxx xxxxxxx will be xxxxxxx ip address xxxxxxx the telnet xxxxxxx say 1.2.3.4.

4) xxxxxxx server sends xxxxxxx the information xxxxxxx xxxxxxx packet xxxxxxx can easily xxxxxxx them and xxxxxxx those xxxxxxx xxxxxxx Proxy firewall xxxxxxx information about xxxxxxx internal network xxxxxxx not about xxxxxxx the network. xxxxxxx if any xxxxxxx xxxxxxx to xxxxxxx sent out xxxxxxx inside the xxxxxxx it xxxxxxx xxxxxxx the destination xxxxxxx of the xxxxxxx with which xxxxxxx has to xxxxxxx The destination xxxxxxx address put xxxxxxx xxxxxxx header xxxxxxx packet #1 xxxxxxx be the xxxxxxx address xxxxxxx xxxxxxx telnet server, xxxxxxx 1.2.3.4.

7) The xxxxxxx Firewall will xxxxxxx let the xxxxxxx directly go xxxxxxx the firewall xxxxxxx xxxxxxx has xxxxxxx hide the xxxxxxx of the xxxxxxx network. xxxxxxx xxxxxxx do that xxxxxxx has to xxxxxxx the contents xxxxxxx the header xxxxxxx check the xxxxxxx in the xxxxxxx xxxxxxx changes xxxxxxx source ip xxxxxxx The source xxxxxxx address xxxxxxx xxxxxxx header will xxxxxxx the ip xxxxxxx of the xxxxxxx firewall server, xxxxxxx 1.4.6.9.

9) The xxxxxxx IP address xxxxxxx xxxxxxx the xxxxxxx of packet xxxxxxx will be xxxxxxx ip xxxxxxx xxxxxxx the proxy xxxxxxx server, say xxxxxxx When this xxxxxxx #2 leaves xxxxxxx Proxy Firewall, xxxxxxx source IP xxxxxxx xxxxxxx the xxxxxxx will be xxxxxxx ip address xxxxxxx the xxxxxxx xxxxxxx proxy client xxxxxxx is actually xxxxxxx with the xxxxxxx server.

11) Firewall xxxxxxx for the xxxxxxx Router to xxxxxxx xxxxxxx outgoing xxxxxxx connection requests xxxxxxx Alice’s desktop xxxxxxx a xxxxxxx xxxxxxx border="1" cellpadding="0" xxxxxxx style="width:71px;">

Rule ID

Source xxxxxxx style="width:71px;">

Destination IP

Source xxxxxxx style="width:71px;">

Destination Port

B

130.3.20.2

External

*

23

Deny

12) xxxxxxx xxxxxxx for the xxxxxxx Router to xxxxxxx incoming TCP xxxxxxx to reach xxxxxxx Web server

 

Packet xxxxxxx style="width:71px;">

Source IP

Protocol xxxxxxx style="width:71px;">

Source xxxxxxx xxxxxxx Port

ACK

D

Outgoing

External

TCP

23

0 xxxxxxx 1

Permit

13) xxxxxxx destination IP xxxxxxx xxxxxxx be xxxxxxx ip address xxxxxxx the email xxxxxxx say xxxxxxx xxxxxxx packet #1 xxxxxxx the Email xxxxxxx the source xxxxxxx address of xxxxxxx header will xxxxxxx the ip xxxxxxx xxxxxxx the xxxxxxx server, say xxxxxxx 4 firewall xxxxxxx are:

 

Rule xxxxxxx style="width:70px;">

Packet Direction

Destination xxxxxxx style="width:69px;">

Protocol name

Destination xxxxxxx style="width:60px;">

ACK

Decision

130.3.20.2

TCP

*

*

Deny

Incoming

TCP

23

*

Deny

Outgoing

Internal

TCP

*

0 or xxxxxxx style="width:69px;">

Permit

E

Internal

23

*

Permit

16) Three xxxxxxx differences xxxxxxx xxxxxxx filtering firewalls xxxxxxx proxy server xxxxxxx are:

 

packet filtering xxxxxxx server firewalls
Actual xxxxxxx directly installed xxxxxxx xxxxxxx network Proxy xxxxxxx present in xxxxxxx network
Faster and xxxxxxx transparent Slower xxxxxxx xxxxxxx so transparent
Susceptible xxxxxxx IP spoofing Not xxxxxxx to IP xxxxxxx accepts or xxxxxxx packets based xxxxxxx firewall rule xxxxxxx xxxxxxx on xxxxxxx firewall It accepts xxxxxxx rejects packets xxxxxxx on xxxxxxx xxxxxxx security policy.

 

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