How are these two Macintosh computers connected? Via a router? The way hostnames like macbookpro.local work is they are broadcast on the network via Bonjour which is simply Apple’s fancy name for broadcast/multicast network services:
Bonjour, also known as zero-configuration networking, enables automatic discovery of devices and services on a local network using industry standard IP protocols.
So if these two Macintosh computers are on the same network sharing the same router, if that router is blocking broadcast/multicast network services then the hostname macbookpro.local will not be able to be found since it will be blocked from the router.
The first think I would recommend is that you login to your router—whatever model it might be—and tool around the menus to see of a broadcast/multicast option is set to filter or block broadcast/multicast traffic. But looking at the details on your router—Actiontec T1200H ADSL Wi-Fi router (PDF of the manual available here)—it does not seem there is even a way to block broadcast/multicast network traffic. So my next idea would be to see if somehow there are firewall settings in the Macintosh’s themselves getting in the way of Bonjour not working? Might be worth it to disable the firewall to at least test the theory for now.
Looking at the firewall options I have in my Mac OS X 10.9.5 (Mavericks) install, it seems that unchecking the “Block all incoming connections” checkbox while the firewall is enabled will allow your firewall to be active while still allowing Bonjour services to be passed through to the system.
When the firewall is on click on the “Firewall Options…” button and you will see this screen with that “Block all incoming connections” checkbox:
On a related note, you can debug this stuff—as explained in this answer I posted here—by testing the network with arp and dns-sd from the Mac OS X “Terminal” like this. For example, to use arp to see what devices are on the network just type in this command and hit return:
arp -a
The output returned if broadcast/multicast traffic is being sent to your computer would be something like this:
computer-name.local (123.456.789.0) at 00:aa:bb:cc:dd:ee on en0 ifscope [ethernet] ? (192.168.2.2) at bb:88:99:cc:77:aa on bridge100 ifscope [bridge]
That shows me that computer-name.local has an IP address of 123.456.789.0 and the bridged connection used by the ad-hoc network where I am sharing my Ethernet connection via Wi-Fi is 192.168.2.2.
And you can also use dns-sd (Multicast DNS (mDNS) & DNS Service Discovery (DNS-SD) Test Tool) from the “Terminal” like this to see if your computer is picking up the hostname of the other machine:
dns-sd -q [name of computer].local
This assumes you know the name of the computer already and broadcast/multicast is working; replace [name of computer].local with that computer name. Then the output would be something like this; note the 123.456.789.0 is a fake IP address for example’s sake:
Timestamp A/R Flags if Name Type Class Rdata 19:56:22.856 Add 2 4 [name of computer].local. Addr IN 123.456.789.0
