+ -- set{sock,peer}name can fail, eg because of local routing table
+ -- if so, try the next server
+ ok, err = sock:setsockname('*', 0);
+ if not ok then return self:servfail(sock, err); end
+ ok, err = sock:setpeername(peer, 53);
+ if not ok then return self:servfail(sock, err); end