I have an iPhone 6 and an old iPad, and they are connected to my wifi and are browsing the internet fine.
I'm also able to reach the config page of my router at 192.168.1.1 from both devices.
Until today, they were also able to browse my LAN to show sites I'm developing on my local server (e.g. 192.168.1.120).
Now, however, neither iOS device is able to connect to LAN IPs other than the router homepage at 192.168.1.1.
I've tried rebooting both devices, rebooting my router and cable modem, restoring my router settings to an earlier version, etc.
Using the "Network Tools" app by KeepSolid on iPhone shows that Trace Route works for normal sites but then fails for LAN sites such as 192.168.1.120.
I have no idea what changed today. The only thing I can think of is that my girlfriend took her Macbook out of town. But I have no idea how that could affect the rest of the LAN. She is not running a server on it.
What else can I try to diagnose and fix this problem?
Update: The "Network Tools" iPhone app has a DNS lookup utility. When I type in my local hostnames, they point to the proper IP addresses as the "A" record. Other records (AAAA, MX, NS, SOA, SRV, and TXT all say "DNS server returned answer with no data"). I don't really know what this means, and I guess it might all be irrelevant since hostname resolution is useless if my devices can't even visit an IP address directly in a browser.
Best Answer
It's looking likely that the problem is a bug in the DD-WRT firmware on my Netgear WNDR3700 router.
I haven't been able to fix it yet.
People in that thread suggest that running the following commands in the router would be a suitable workaround, but I haven't gotten them to work yet:
UPDATE: Oops, it's potentially not a bug in that firmware; I am even having problems after swapping out the router. But since this other router uses DD-WRT too (although a much earlier version of the firmware), I'm leaving this answer here since it's still my best guess and might help someone.