LCA Network Configuration & Troubleshooting 4

Question 1

Which command tests whether TCP port 80 on host 203.0.113.5 is open without using nmap?

Accepted Answer

nc -zv 203.0.113.5 80

Answer

'nc -zv host port' attempts a TCP connection without sending data (-z) and reports the result verbosely (-v).

Question 2

A Linux host with IP 192.168.10.5 needs to masquerade traffic to the internet through eth0. Which iptables command achieves this?

Accepted Answer

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

Answer

MASQUERADE in the nat table's POSTROUTING chain dynamically replaces the source IP with the outgoing interface's address.

Question 3

What does the 'ip link set eth0 mtu 9000' command do?

Accepted Answer

Configures the MTU of eth0 to 9000 bytes for jumbo frames

Answer

Setting MTU to 9000 enables jumbo frames, which can improve throughput on high-speed LAN segments that support it.

Question 4

Which configuration directive in /etc/resolv.conf allows the resolver to try multiple domain suffixes when resolving a short hostname?

Accepted Answer

search

Answer

The 'search' directive specifies a list of domain suffixes appended when a hostname without dots is queried.

Question 5

You observe high retransmission rates in 'ss -s' output. What does this most likely indicate?

Accepted Answer

Network congestion or packet loss causing TCP to resend unacknowledged segments

Answer

TCP retransmissions occur when acknowledgments are not received in time, typically due to packet loss or congestion.

(LCA) Certified Linux Administrator Practice Test