(1) Stack Info

DNS Server

  • CentOS 5.6 64bit running dnsmasq 2.45 on IP
  • Serving as DNS-Only Server using it's local /etc/hosts. /etc/resolv.conf on this machine has


  • Draytek Vigor 2910G configured as DHCP Server and using, as default DNS Server
  • (Assigning DHCP IP range served 10.9.8.*)

Network client with Problem

  • iMac with OS X Lion 10.7.4 with Ethernet DNS on "autoconfig", i.e., are shown as grey entries in DNS

All other local machines (webservers, etc) have fixed IPs 10.9.8.xx. Unix and Windows machines do not experience the problem.

(2) config files

dnsmasq machine /etc/resolv.conf

search lan

dnsmasq machine /etc/hosts (only the entry for idevsrv)        idevsrv idevsrv.lan

OS X Lion /etc/resolv.conf


(3) Observations

Irregularly and currently irreproducible, name resolving for local servers (named by dnsmasq) via mDNSResponder works and then works not.

Tools using mDNSResponder, like ping, browsers, subversion cannot resolve a hostname, while dig (not using mDNSResponder) works. Using 'dscacheutil -flushcache' gets ping working again, yet I cannot predict when it will stop working again:

$ ping idevsrv
ping: cannot resolve idevsrv: Unknown host

$ dig idevsrv

; <<>> DiG 9.7.3-P3 <<>> idevsrv
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 24510
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;idevsrv.           IN  A

idevsrv.        0   IN  A

;; Query time: 9 msec
;; WHEN: Tue Jun 19 16:33:37 2012
;; MSG SIZE  rcvd: 41

$ dscacheutil -flushcache
$ ping idevsrv
PING idevsrv ( 56 data bytes
64 bytes from icmp_seq=0 ttl=64 time=0.310 ms

I have several servers including servers that need constant availability of hostnames (e.g. web, subversion) so constant availability is greatly appreciated by the team:)

After searching the web for hours I still did not find any useful information that goes further than flushing the dns cache which does not suffice.

(4) Question(s)

(in order of benefit:)

  • How could I avoid the disconnect? (but stil use my local dnsmasq dns server:)
  • How might I identify the reason for the disconnection?
  • If you have better search terms than the usual suspects, please paste your search url :)

Many thanx in advance!

Note: this question is moved from stackoverflow to this site.

  • New info: dscacheutil -flushcache does not always remedy the problem! $ dscacheutil -flushcache $ ping ctf611 ping: cannot resolve ctf611: Unknown host
    – Volker
    Jun 22, 2012 at 12:25


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