I got this question at a job interview, but I did not know the answer. I think they expected some shell command or packages, which can help react to the attack.
Assume that, you are a system admin and you work for the Nokia Networks. This server store customers details and communicate with them when a customer want to report a problem or bug through the global and 2 internal networks. The attackers are using DNS-poison and they can also start the attack from the internal network, but these details were not specified.
I know it could be a linux question, but actually it is connecting to the IT security too.