A colleague lists five nameserver lines in /etc/resolv.conf so that the host has plenty of fallbacks. On a glibc system, what happens to the fourth and fifth entries?
LPIC-1 Exam 102-500, objective 109. Networking fundamentals easy
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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 They are ignored; the resolver uses at most three nameservers.
Correct. The glibc resolver compiles in a limit of MAXNS name servers, currently 3, and silently disregards any listed beyond that.
Not correct They are used only if the search list fails to qualify the name.
Wrong. The search list controls how unqualified names are expanded and has no bearing on which nameserver lines are usable.
Not correct They are used, but only for reverse lookups.
Wrong. Nameserver entries are not split by query type; the same servers answer forward and reverse queries.
Not correct The whole file is rejected as malformed and resolution falls back to /etc/hosts only.
Wrong. The resolver parses what it understands and ignores the rest; it does not discard the file over a surplus entry.
Why
resolv.conf accepts up to MAXNS nameserver lines, a compile-time constant that is 3 in glibc, and entries past the third are ignored. The resolver queries them in the order listed, moving on only after a timeout, so ordering matters more than quantity. If you need more resolvers or genuine failover, that belongs in a local caching resolver rather than in resolv.conf.
Where this comes from
- Cited
- manual page resolv.conf(5)
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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