LPI 202-450 Exam With Confidence Using Practice Dumps

An open relay is a mail server that allows anyone to send e-mail through it without authentication or authorization. This can expose the mail server to spam, abuse, and blacklisting. To prevent the mail server from being used as an open relay, while maintaining the possibility to receive company mails, the following actions would help:

• Restrict Postfix to only accept e-mail for domains hosted on this server. This can be done by setting the mydestination parameter in the /etc/postfix/main.cf file to include the company domains, and the smtpd_recipient_restrictions parameter to reject_unauth_destination. This will ensure that Postfix will only accept mail for the domains that it is responsible for, and reject mail for other domains unless the sender is authenticated or authorized. For example:

mydestination = example.com, example.net, localhost smtpd_recipient_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination

• Restrict Postfix to only relay outbound SMTP from the internal network. This can be done by setting the mynetworks parameter in the /etc/postfix/main.cf file to include the IP addresses or networks of the internal hosts that are allowed to relay mail through Postfix, and the smtpd_relay_restrictions parameter to permit_mynetworks. This will ensure that Postfix will only relay mail from the trusted internal hosts, and reject mail from external hosts unless the sender is authenticated or authorized. For example:

mynetworks = 192.168.0.0/24, 127.0.0.0/8 smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, defer_unauth_destination

The other actions would not help prevent the mail server from being used as an open relay, or they would affect the functionality of the mail server. Configuring Dovecot to support IMAP connectivity would not affect the SMTP relay, but it would allow users to access their mailboxes remotely. Configuring netfilter to not permit port 25 traffic on the public network would prevent the mail server from receiving any mail from the outside world, which would defeat the purpose of having a mail server. Upgrading the mailbox format from mbox to maildir would not affect the SMTP relay, but it would change the way the mail messages are stored on the disk.

References:

• LPIC-2 Exam 202 Objectives, Objective 205.3: Managing a postfix server
• Postfix Basic Configuration, Postfix Documentation
• Postfix SMTP relay and access control, Postfix Documentation
• How to disable open relay on Postfix? - Howtoforge, Forum
• Postfix SMTP relay without authentication | Guide - Bobcares, Blog

 The ErrorLog directive of the Apache HTTPD server defines the location and name of the file where the server will log any errors it encounters. The default value of this directive is logs/error_log, which means that the error log file will be stored in the logs subdirectory of the server root directory. The ErrorLog directive can also accept a filename relative to the server root, an absolute filename, or a pipe to a program that will handle the logging. For example, ErrorLog logs/my_error_log will store the error log file in the logs subdirectory with the name my_error_log, ErrorLog /var/log/httpd/error_log will store the error log file in the /var/log/httpd directory with the name error_log, and ErrorLog “|bin/rotatelogs logs/error_log 86400” will pipe the error log to the rotatelogs program that will rotate the log file every 86400 seconds. References: Log Files - Apache HTTP Server Version 2.4, Directive Quick Reference - Apache HTTP Server Version 2.4, How do I find Apache http server log files? – Code A Site Blog, mod_log_config - Apache HTTP Server Version 2.2

To allow X connections to be forwarded from or through an SSH server, the configuration keyword that must be set to yes in the sshd configuration file is XllForwarding. This keyword enables X11 forwarding, which is a mechanism that allows graphical applications to be run on a remote host and displayed on a local host. The sshd configuration file is usually located at /etc/ssh/sshd_config, and the XllForwarding keyword can be set globally or per host. For example:

XllForwarding yes

This will enable X11 forwarding for all hosts. To enable X11 forwarding for a specific host, use the Match directive, followed by the Host keyword and the host name or pattern. For example:

Match Host example.com XllForwarding yes

This will enable X11 forwarding only for the host example.com.

References:

• X11 Forwarding using SSH
• sshd_config - OpenSSH SSH daemon configuration file
• How To Configure X11 Forwarding Using SSH In Linux