How to get the machine name from an IP via Multicast DNS

mdns

I have a list of IP addresses on a network, and most of them support multicast DNS. I'd like to be able to resolve the server name instead of just having the IP address.

ping computer.local
64 bytes from 192.168.0.52: icmp_seq=1 ttl=64 time=5.510 ms
64 bytes from 192.168.0.52: icmp_seq=2 ttl=64 time=5.396 ms
64 bytes from 192.168.0.52: icmp_seq=3 ttl=64 time=5.273 ms

Works, but I'd like to be able to determine that name from the IP. Also the devices don't necessarily broadcast any services, but definitely do support mDNS broadcast. So looking through services won't work.

Best Answer

Since you already know the IP addresses you can look up the reverse entry for each IP address to get the associated forward address:

$ dig -x 10.0.0.200 @224.0.0.251 -p 5353

; <<>> DiG 9.6.0-APPLE-P2 <<>> -x 10.0.0.200 @224.0.0.251 -p 5353
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 54300
;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; QUESTION SECTION:
;200.0.0.10.in-addr.arpa.   IN  PTR

;; ANSWER SECTION:
200.0.0.10.in-addr.arpa. 10 IN  PTR atj-mbp.local.

;; ADDITIONAL SECTION:
atj-mbp._device-info._tcp.local. 10 IN  TXT "model=MacBookPro3,1"

;; Query time: 2 msec
;; SERVER: 10.0.0.200#5353(224.0.0.251)
;; WHEN: Sat Jun 26 07:53:44 2010
;; MSG SIZE  rcvd: 126

For a more shell script friendly output, use '+short':

$ dig +short -x 10.0.0.200 @224.0.0.251 -p 5353
atj-mbp.local.

Depending on your intended use case there may be a more appropriate method of performing the query. Feel free to contact me if you should need any further information.

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