LPI 202-450 Questions Answers

The option in named.conf that specifies which hosts are permitted to ask for domain name information from the server is allow-query. The allow-query option is used to define an access control list (ACL) that matches the source IP address of the DNS query. The ACL can be a list of IP addresses, networks, keywords, or predefined ACL names. The default value of allow-query is any, which means that any host can query the server. However, this can pose a security risk, as the server may be exposed to unwanted or malicious queries. Therefore, it is recommended to restrict the allow-query option to only the hosts that need to access the server, such as the local network or trusted clients. For example, the following option allows only the hosts in the 192.168.1.0/24 network and the localhost to query the server:

allow-query { 192.168.1.0/24; localhost; };

The other options are not valid in named.conf. allowed-hosts, accept-query, permit-query, and query-group are not recognized keywords by BIND.

References:

• LPIC-2 exam 202 objectives, topic 208.1, “Implementing a web server”
• BIND 9 Administrator Reference Manual, chapter 6, “Access Control Lists and TSIG”
• How to Configure DNS Server with TSIG on CentOS 8

The http_port directive in squid.conf sets the port number or numbers that Squid will use to listen for client requests. You can specify multiple socket addresses with different port numbers and options. By default, Squid listens on port 3128 on all network interfaces. You can change the port number or bind the socket to a specific IP address if needed. For example, to set the port to 8080, you can write:

http_port 8080

To configure Squid to listen only on the 192.0.2.1 IP address on port 3128, you can write:

http_port 192.0.2.1:3128

References:

• Squid proxy configuration tutorial on Linux
• squid : http_port configuration directive
• Configuring the Squid Service to Listen on a Specific Port or IP Address

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

The http_access directive for Squid allows or denies access to the web resources based on defined access control lists (ACLs). The syntax of the http_access directive is:

http_access allow|deny [!]aclname …

The directive takes one or more ACL names as arguments, separated by spaces. The first argument is either allow or deny, indicating the action to be taken if the ACLs match. The optional ! character before an ACL name negates the result of that ACL.

To allow users in the ACL named sales_net to only access the Internet at times specified in the time_acl named sales_time, the correct http_access directive is:

http_access allow sales_net sales_time

This directive means that if the client IP address matches the sales_net ACL and the request time matches the sales_time ACL, then the access is allowed. Otherwise, the access is denied or the next http_access directive is evaluated.