my MBP's .local hostname is no longer resolvable

Try using Network Utility, located in /System/Library/CoreServices/Applications/. It has a ping function.

27" i7 iMac (Mid 2011) refurb, OS X Yo (10.10.1), Mavs, ML & SL, G4 450 MP w/10.5 & 9.2.2

If you visit System Preferences > Security & Privacy > Firewall — in Firewall Options is the Enable Stealth mode check box. If it is checked it will block all ICMP packets, including those you originate in the Terminal to localhost. If you temporarily uncheck Stealth Mode in the Security settings, your Terminal based ping syntax will work correctly with localhost.

On my machine, with the computer name = localhost, I get:

dig localhost.local

; <<>> DiG 9.6-ESV-R4-P3 <<>> localhost.local

;; global options: +cmd

;; Got answer:

;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 28607

;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:

;localhost.local. IN A

;; ANSWER SECTION:

localhost.local. 10 IN A 198.105.244.228

localhost.local. 10 IN A 198.105.254.228

;; Query time: 16 msec

;; SERVER: 192.168.0.1#53(192.168.0.1)

;; WHEN: Wed Dec 10 16:31:02 2014

;; MSG SIZE rcvd: 65

When I perform a ping `hostname` (with the Firewall stealth off), the ip address is shown in the ping output for me.

dig +short `hostname` returns blank for me.

python -c 'import socket; print socket.gethostbyname("myhost.local")' returns my machine's current ip address.

So does the following syntax:

ping -q -c 1 -t 1 your_host_here | grep PING | sed -e "s/).*//" | sed -e "s/.*(//"

I wonder if the /etc/hosts file has been edited. Placing the machine name, and localhost on the same line has been known to cause issues in past OS X releases.

Stop me if I am missing something, but are you certain that mdns entries will be resolved by these tools?

I also get no answer section for 'dig myhostname.local' (on 10.9).

I think this depends on your local network setup (e.g. a router that manages mDNS, like Apples Airport etc).

Isn't dns-sd is the tool for troubleshooting bonjour?

dns-sd -q Myhostname.local

…

12:05:58.236 Add 2 4 Myhostname.local. Addr IN 192.168.12.35

Also have you tested on other networks? I think it's possible for admins to block bonjour, it's unclear (at least to me) if services are resolvable locally with these tools…

See the Mac OS X NOTICE section in the nslookup manual, it doesn't use the same resolution methods as other parts of the OS for DNS, mDNS is not mentioned, I'm not certain you are testing correctly.

Bonjour bowser will show advertised services, it's a bit easier than dns-sd.

http://tildesoft.com - don't let the minimalist site scare you, it is a handy app.

The hostname isn't necessarily the same as the Bonjour name, which you can see in the Sharing preference pane. Domain names in the ".local" TLD are reserved for Bonjour and will not resolve via unicast DNS.