CecilWard
Posts: 39
Joined: Sat Sep 03, 2016 10:17 pm

Bizarre long name of pi visible on Lan

Tue Sep 12, 2017 1:48 am

The rest of the Lan is seeing a bizarre very long name for the pi, which is
dhcpcd-671linux-4935-v7armv7lbcm2835.site01.cecilward.com

and not based on raspberry-pi-1.* as I set the host name to be using raspi-config. I can't ping "raspberry-pi-1." or "raspberrypi.site01.cecilward.com." (the expected site01.cecilward.com being the domain name part that is successfully suffixed onto every other machine's name) A Lan scanning app says that the 'hostname' itself is something hugely long, and the dhcp name is as expected, whatever that means.

User avatar
DougieLawson
Posts: 36313
Joined: Sun Jun 16, 2013 11:19 pm
Location: Basingstoke, UK
Contact: Website Twitter

Re: Bizarre long name of pi visible on Lan

Tue Sep 12, 2017 7:09 am

That funky name is the result of a reverse DNS lookup. You give an IP address to your DNS, it returns the domain name.

dig -x 192.168.3.14

Code: Select all

pi@viking ~ $ dig -x 192.168.3.14

; <<>> DiG 9.10.3-P4-Raspbian <<>> -x 192.168.3.14
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 10129
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;14.3.168.192.in-addr.arpa.                IN      PTR

;; ANSWER SECTION:
14.3.168.192.in-addr.arpa. 259200  IN      PTR     dhcp-192-168-3-14.example.co.uk.

;; AUTHORITY SECTION:
3.168.192.in-addr.arpa.    259200  IN      NS      example.co.uk.

;; Query time: 4 msec
;; SERVER: 2001:???:????:???::1#53(2001:???:????:???::1)
;; WHEN: Tue Sep 12 07:00:58 UTC 2017
;; MSG SIZE  rcvd: 114
Normal DNS lookup works with a domain name and returns an IP addr

Code: Select all

pi@viking ~ $ dig dhcp-192-168-3-14.example.co.uk.

; <<>> DiG 9.10.3-P4-Raspbian <<>> dhcp-192-168-3-14.example.co.uk.
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 63934
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 4

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;dhcp-192-168-3-14.example.co.uk. IN        A

;; ANSWER SECTION:
dhcp-192-168-3-14.example.co.uk. 259200 IN A 192.168.3.14

;; AUTHORITY SECTION:
example.co.uk.   259200  IN      NS      ns.example.co.uk.

;; ADDITIONAL SECTION:
ns.example.co.uk. 259200 IN      A       192.168.3.11
ns.example.co.uk. 259200 IN      AAAA    2001:???:????:???::1
ns.example.co.uk. 259200 IN      AAAA    2001:???:????:???:ba27:ebff:fe85:c936

;; Query time: 3 msec
;; SERVER: 2001:???:????:???::1#53(2001:???:????:???::1)
;; WHEN: Tue Sep 12 07:04:24 UTC 2017
;; MSG SIZE  rcvd: 169
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