XK0-005 Question #10: Real Exam Question with Answer & Explanation

Question

A Linux administrator has configured a Linux system to be used as a router. The administrator confirms that two network adapters are properly installed and functioning correctly. In addition, the output of the iptables -L command appears to contain a complete firewall configuration. Which of the following commands does the administrator need to issue for the router to be fully functional?

Options

• Aecho "1" > /proc/sys/net/ipv4/ip_forward
• Becho "0" > /proc/sys/net/ipv4/tcp_abort_on_overflow
• Cecho "0" > /proc/sys/net/ipv4/max_connections
• Decho "1" > /proc/sys/net/ipv4/ip_default_ttl

Explanation

For a Linux system to function as a router and forward IP packets between network interfaces, IP forwarding must be explicitly enabled.

Common mistakes.

• B. tcp_abort_on_overflow configures TCP behavior when listen queues are full, which is unrelated to basic IP packet forwarding for routing.
• C. There is no standard /proc/sys/net/ipv4/max_connections parameter that directly controls IP forwarding; such parameters relate to connection limits, not routing functionality.
• D. ip_default_ttl sets the default Time-To-Live value for outgoing packets, which affects packet hop limits but does not enable the core IP forwarding mechanism itself.

Concept tested. Linux IP forwarding for routing

Reference. https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/networking_guide/sec-ip_forwarding

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