Question#1: SMTP (Simple Mail Transfer Protocol is the standard protocol for tra

Question

Question#1: SMTP (Simple Mail Transfer Protocol is the standard protocol for transferring mail between hosts over TCP. A TCP connection is set up between a user agent and a server program. The server listens on TCP port 25 for incoming connection requests. The user end of the connection is on a TCP port number above 1023. Suppose you wish to build a packet filter rule set allowing inbound and outbound SMTP traffic. You generate the following rule set Rule Direction Src Addr Dest Addr Protocol Dest Port Action External Internal TCP Permit Out Internal External TCP 1023 Permit C Out Internal External TCP 25 Permit In External Internal TCP >1023 Permit Any Any Any Any Deny E Either a) Describe the effect of each rule. b) Your host in this example has IP address 172.16.1.1. Someone tries to send e-mail from a remote host with IP address 192.168.3.4. If successful, this generates an SMTP dialogue between the remote user and the SMTP server on your host consisting of SMTP commands and mail. Additionally, assume that a user on your host tries to send e-mail to the SMTP server on the remote system. Four typical packets for this scenario are as shown

Explanation / Answer

a:   Here is the description of each rule as follows:

      Rule A : Allows the packet through the filter to server , generates from External network to internal network

      Rule B : Allows the packet through the filter from user ,generates from internal network to external network

      Rule C : Allows the packet through the filter from server , generates from internal network to external network

      Rule D : Allows the packet through the filter to user, generates from External network to internal network

      Rule E : Don't let packet to either of server or user network.

b: Four typical packet for this scenario as follows :

  

Packet Direction Src_Addr Des_Addr Protocol Dest Port Action      1        IN 192.168.3.4 172.16.1.1      TCP        25 PERMIT      2       OUT 172.16.1.1 192.168.3.4      TCP     1048 PERMIT      3       OUT 172.16.1.1 192.168.3.4    TCP        25 PERMIT      4      IN 192.168.3.4 172.16.1.1      TCP     1556 PERMIT

Related Questions

Navigate

• Browse (All)
• Browse Q
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.