A server has two interfaces, eth0 on the office LAN and eth1 on a storage network. You must verify that 203.0.113.9 answers when the echo requests leave through eth1, not through whichever interface routing would normally choose. Which command does that?
LPIC-1 Exam 102-500, objective 109. Networking fundamentals medium
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How these questions are written — where each question comes from, what the verification ledger records, and what happens when one is found wrong.
The options
Correct ping -I eth1 203.0.113.9
Correct. -I takes an interface name or a source address and binds the echo requests to it, so the packets are sourced from eth1 regardless of the route the kernel would otherwise select.
Not correct ping -i eth1 203.0.113.9
Wrong. Lowercase -i sets the interval in seconds between outgoing packets and expects a number, so an interface name is rejected as a bad timing value.
Not correct ping -s eth1 203.0.113.9
Wrong. -s sets the number of payload data bytes in each echo request, 56 by default, giving 64-byte ICMP packets. It takes a size, not an interface.
Not correct ping -w eth1 203.0.113.9
Wrong. -w is the deadline in seconds after which ping exits regardless of how many packets have been sent or received.
Why
On a multi-homed host the source address decides which return path a reply takes, so testing an interface means pinning the source rather than trusting the routing table. `ping -I` accepts either the device name or one of its addresses, and it is the only ping option that changes the egress interface. Case matters throughout iputils ping: -i is the send interval and -I is the interface, just as -t is the TTL and -T is the timestamp option.
Where this comes from
- Cited
- manual page ping(8)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 109 and space the ones you get wrong.
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