So, the primary nameserver is down but luckily
/etc/resolv.conf has been equipped with a secodary nameserver entry - great! And
nslookup works like a charm too, heh! But all the other useful tools are waiting for ages until they'll get a response from the backup server - why is that?
$ time ping eve eve is alive real 0m30.045s user 0m0.007s sys 0m0.018sOther than e.g.
nslookup, the normal applications have to use the the resolver(4) to get their name requests answered. Now, we could cheat and put our backup server before the faulty one, but let's see if we can tackle this from a different angle. resolv.conf(4) was most helpful, of course:
options Allows certain internal resolver variables to be modified. timeout:n / retrans:n Sets the amount of time the resolver will wait for a response from a remote name server before retrying the query by means of a different name server. Measured in seconds, the default is RES_TIMEOUT. SeeIn our
attempts:n / retry:n Sets the number of times the resolver will send a query to its name servers before giving up and returning an error to the calling application. The default is RES_DFLRETRY. See .
resolv.h(Solaris 10) we have :
$ egrep 'RES_TIMEOUT|RES_MAXRETRANS|RES_DFLRETRY' /usr/include/resolv.h #define RES_TIMEOUT 5 /* min. seconds between retries */ #define RES_MAXRETRANS 30 /* only for resolv.conf/RES_OPTIONS */ #define RES_DFLRETRY 2 /* Default #/tries. */So, let's tweak those
$ grep options /etc/resolv.conf options timeout:1 retry:1 $ time ping eve eve is alive real 0m7.794s user 0m0.007s sys 0m0.018sWhooha, not bad.
Note: in Linux the retry: parameter is called attempts:
Let's tweak the retry: parameter a bit more:
$ grep options /etc/resolv.conf options timeout:1 retry:0 $ time ping eve eve is alive real 0m2.100s user 0m0.007s sys 0m0.018sEven better. Of course, one has to realize that with zero retries the resolver will jump to the next nameserver on the first failure - so, if our backup server is a bit sleepy we won't get a reply at all. If you enable nscd, subsequent requests to the same name will be answered instantly:
$ sudo svcadm enable svc:/system/name-service-cache $ time ping eve eve is alive real 0m3.218s user 0m0.007s sys 0m0.018s $ time ping eve eve is alive real 0m0.198s user 0m0.007s sys 0m0.017s