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SMTP (Simple Mail Transfer Protocol) is the standard protocol for transferring mail between hosts over Transmission Control Protocol (TCP). A TCP connection is set up between a user agent and a server program. The server listens on TCP port 25 for ncoming 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 A B C D E In Out Out In Either External Internal Internal External TCP Internal External External Any Internal TCP Any TCP TCP Any 25 > 1023 Permit Permit 25 Permit Any > 1023 Permit Deny 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 will generate an SMTP dialogue, consisting of SMTP commands and mail, between the remote user and the SMTP server on your host. Assume that a user on your host tries to send packets for this scenario as shown: Scenario Direction 1 2 In Out Src Addr Dest Addr Protocol Dest Action Port 192.168.3.4 172.16.1.1 TCP 172.16.1.1 192.168.3.4 TCP 25 ? 1234 ? Indicate which packets are permitted or denied, and which rule is used in each case.

SMTP (Simple Mail Transfer Protocol) is the standard protocol for transferring mail between hosts over Transmission Control Protocol (TCP). A TCP connection is set up between a user agent and a server program. The server listens on TCP port 25 for ncoming 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 A B C D E In Out Out In Either External Internal Internal External TCP Internal External External Any Internal TCP Any TCP TCP Any 25 > 1023 Permit Permit 25 Permit Any > 1023 Permit Deny 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 will generate an SMTP dialogue, consisting of SMTP commands and mail, between the remote user and the SMTP server on your host. Assume that a user on your host tries to send packets for this scenario as shown: Scenario Direction 1 2 In Out Src Addr Dest Addr Protocol Dest Action Port 192.168.3.4 172.16.1.1 TCP 172.16.1.1 192.168.3.4 TCP 25 ? 1234 ? Indicate which packets are permitted or denied, and which rule is used in each case.

Database System Concepts
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
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SMTP (Simple Mail Transfer Protocol) is the standard protocol for transferring mail between hosts over Transmission Control Protocol (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 A B с D E In Out Out Either External Internal External Internal Internal External Any External Internal Any TCP TCP TCP TCP Any 25 Permit > 1023 Permit 25 Permit > 1023 Permit Any Deny 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 will generate an SMTP dialogue, consisting of SMTP commands and mail, between the remote user and the SMTP server on your host. Assume that a user on your host tries to send packets for this scenario as shown: Scenario Direction 1 2 In Out Src Addr Dest Addr Protocol Dest Dest Action Port 192.168.3.4 172.16.1.1 TCP 172.16.1.1 192.168.3.4 TCP 25 1234 ? ? Indicate which packets are permitted or denied, and which rule is used in each case.
Transcribed Image Text:SMTP (Simple Mail Transfer Protocol) is the standard protocol for transferring mail between hosts over Transmission Control Protocol (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 A B с D E In Out Out Either External Internal External Internal Internal External Any External Internal Any TCP TCP TCP TCP Any 25 Permit > 1023 Permit 25 Permit > 1023 Permit Any Deny 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 will generate an SMTP dialogue, consisting of SMTP commands and mail, between the remote user and the SMTP server on your host. Assume that a user on your host tries to send packets for this scenario as shown: Scenario Direction 1 2 In Out Src Addr Dest Addr Protocol Dest Dest Action Port 192.168.3.4 172.16.1.1 TCP 172.16.1.1 192.168.3.4 TCP 25 1234 ? ? Indicate which packets are permitted or denied, and which rule is used in each case.
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