On Thu, Jul 5, 2012 at 10:02 AM, William Herrin <bill@herrin.us> wrote:
Hi folks,
I gave my HR folks a screening question to ask candidates for an IP expert position. I've gotten some "unexpected" answers, so I want to do a sanity check and make sure I'm not asking something unreasonable. And by "unexpected" I don't mean naively incorrect answers, I mean oh-my-God-how-did-you-get-that-cisco-certification answers.
The question was:
You implement a firewall on which you block all ICMP packets. What part of the TCP protocol (not IP in general, TCP specifically) malfunctions as a result?
My questions for you are:
1. As an expert who follows NANOG, do you know the answer? Or is this question too hard?
I perused the thread but lots of people have mentioned mtu discovery but not what happens on TCP and an issue with mss but not what happens - if there is a smaller mtu along the path the receive window fills up on the host initiating the connection and then the connection just times out.
2. Is the question too vague? Is there a clearer way to word it?
It is way to confusing and may be better in a two part question and work up to it. Instead of asking if all ICMP is blocked put into to Type/Code with out giving away that it's the Maybe for HR ask more text book stuff like name the tcp flags or describe the tcp connection closing or what field determines if a packet can be fragmented and then compare that to how it works in IPv6. How big is the TCP or IP headers? How many with options? etc...
3. Is there a better screening question I could pass to HR to ask and check the candidate's response against the supplied answer?
Thanks, Bill Herrin
-- William D. Herrin ................ herrin@dirtside.com bill@herrin.us 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004