+.TP
+.BR single-request " (since glibc 2.10)"
+sets
+.BR RES_SNGLKUP
+in
+.IR _res.options .
+By default, glibc performs IPv4 and IPv6 lookups in parallel since
+version 2.9.
+Some appliance DNS servers
+cannot handle these queries properly and make the requests time out.
+This option disables the behavior and makes glibc perform the IPv6
+and IPv4 requests sequentially (at the cost of some slowdown of the
+resolving process).