Network Configuration & Troubleshooting Flashcards

Which NetworkManager command-line tool is used to bring up a connection profile named 'office-vpn'?

Answer: nmcli con up office-vpn

'nmcli con up ' activates a connection profile managed by NetworkManager.

What is the purpose of the /proc/sys/net/ipv4/ip_forward file?

Answer: It enables or disables kernel IP packet forwarding between interfaces

Writing '1' to ip_forward enables the Linux kernel to forward packets between network interfaces, making it act as a router.

A user reports intermittent packet loss to a remote server. Which tool provides continuous per-hop latency and loss statistics in a single view?

Answer: mtr

'mtr' combines traceroute and ping, continuously updating per-hop packet loss and latency statistics.

Which iptables chain is used to modify packets destined for the local machine before routing decisions are made?

Answer: PREROUTING

The PREROUTING chain (in the nat table) processes incoming packets before the routing decision, used for DNAT.

You need to capture only TCP traffic on port 443 on interface eth0 using tcpdump. Which command is correct?

Answer: tcpdump -i eth0 tcp and port 443

tcpdump uses BPF filter syntax; 'tcp and port 443' captures only TCP packets on port 443.

Which command shows the ARP cache on a Linux system using iproute2?

Answer: ip neigh show

'ip neigh show' displays the neighbor (ARP) table, which maps IP addresses to MAC addresses.

What does setting a network interface to promiscuous mode accomplish?

Answer: It allows the interface to receive all packets on the network segment, not just those addressed to it

Promiscuous mode causes the NIC to pass all frames to the kernel regardless of destination MAC, essential for packet capture tools.