The rejections you got may not have been because you didn't know a specific answer to a very technical question.
Something I've come across in the past is something similar. It's not knowing the specific answer. Sometimes it's knowing what specific answer *they* want.
For example, "How can you change the IP on a current RHEL or CentOS box".
There are a bunch of right answers.
- edit the appropriate /etc/sysconfig/network-scripts/ifcfg-eth* file.
- use ifconfig directly (not durable through a reboot, but ...)
- change the static entry on the dhcp server for that network interface
- modify it in cfengine, and wait for it to update.
... and those could all be wrong. That particular shop may say "We don't trust ifcfg-eth*", "system-config-network mangles the file format", or even "we don't use those files, we use /etc/rc.d/rc.inet1, that the old admin 10 years ago wrote". It could even start with "fill out the production change review forms, and submit them to the change review committee".
Some places insist that you use the full path to scripts, in case someone else put one farther up in your path (like /bin/). Some don't allow sbin to be in the user's path at all. And of course, if you failed to say "use sudo", you're one of those renegade admins who thinks they can run commands as root. Not knowing *their* method, even though you've never worked for them, is enough to fail an interview.
When I've been interviewing people, I don't work from a hard set of answers. If the interviewee comes close enough, they got it right. If they gave the "system-config-network" answer, I'd just ask "Do you know what files that modifies related to IPs?"
I've interviewed with Google a few times. One of the questions they asked was "How does telnet work?" I answered, and the interviewer asked me the question again. I gave the brief description, the detailed description, all the way down to the opening of sockets and how TCP works. Finally I just had to tell him, "I'm not sure what you're looking for in the answer. Can you please clarify the question?" He didn't. I don't know if that was a pass, fail, or just a stress question.