Open Radar

 
Summary:
The most obvious sign of this problem is that a computer will be visible in a Finder window's sidebar, but will be unable to connect. Pinging the computer's IP (e.g., 192.168.1.253) or .local hostname (e.g., iMac.local) will not work (100% packet loss). If I physically go to the computer, it will have Internet access and can see/ping the Time Capsule router, but will also be unable to connect to my computer in the Finder or via pings. I've also experienced similar problems connecting to a printer on the AirPort network. In the case of the printer, I can see the printer's web interface advertised via the Bonjour bookmarks in Safari, but will be unable to connect to that webpage or successfully print.

Steps to Reproduce:
Here is the configuration that I'm using in which the problem appears. It may also appear in other configurations

Time Capsule (Simultaneous Dual-Band):
	Wireless Mode: Create a wireless network
	Radio Mode & Channel Selection: Automatic
	Wireless Security: WPA2 Personal
	Connect Using: Ethernet
	Ethernet WAN Port: Automatic
	Connection Sharing: Share a public IP address
	Configure IPv4: Using DHCP
	DHCP Beginning Address: 192.168.1.2
	DHCP Lease: 1 days
	Enabled default host at: 192.168.1.253
	Enabled NAT Port Mapping Protocol
	IPv6 Mode: Link-local only
	
iMac (AirPort):
	Configure IPv4: Using DHCP with manual address
	IP Address: 192.168.1.253

MacBook Pro (AirPort):
	Configure IPv4: Using DHCP

1. Enable screen and file sharing on the iMac and the MacBook Pro.
2. Attempt to connect to the iMac from the MacBook Pro via a Finder window sidebar.
3. If connection is successful, disconnect and close the Finder window, wait an arbitrary amount of time and try connecting again until it fails.

Expected Results:
All computers and devices on the local AirPort network should be reachable and no connection failures should occur.

Actual Results:
Computers and other devices (printers) will be intermittently unreachable although they are not asleep and can ping the router.

Regression:
At work, if I inactivated all services except AirPort, I couldn't connect to the Mac mini on my desk or print to the office printer. Activating the Ethernet service allowed connections to other Macs and printers as expected.

Notes:
See also http://discussions.apple.com/thread.jspa?threadID=2406418

I've tried turning IPv6 off, inactivating all interfaces except AirPort on all computers, and reseting the Time Capsule. traceroute doesn't help. It seems this is a very deep problem related to AirPort networking in Mac OS X. I don't believe this is a signal strength issue since I encounter this problem with computers in the same room.

22-Apr-2010 01:41 AM:
When I am able to connect, I see these entries in netstat -ral:

Internet:
Destination        Gateway            Flags        Refs      Use    Mtu   Netif Expire
192.168.1.253      0:24:36:b5:7c:55   UHLWI           4      180   1500     en1   1186

Internet6:
Destination                             Gateway                         Flags        Refs      Use    Mtu    Netif Expire
totoro.local                            0:24:36:b5:7c:55                UHLW            0        3   1500      en1

When the connection fails, I see this:

Internet:
Destination        Gateway            Flags        Refs      Use    Mtu   Netif Expire
192.168.1.253      link#5             UHRLWI          1        8   1500     en1      9

Internet6:
Destination                             Gateway                         Flags        Refs      Use    Mtu    Netif Expire
(the totoro.local entry that used to be here is missing)

FWIW, I've had luck in getting this to fail by putting my computer to sleep, waiting a few minutes, waking it up, and then attempting the connection again.

Also, running "dns-sd  -B _afpovertcp._tcp." still shows this computer:

Browsing for _afpovertcp._tcp.
Timestamp     A/R Flags if Domain                    Service Type              Instance Name
 1:36:57.205  Add     3  0 username.members.mac.com.  _afpovertcp._tcp.         Totoro
 1:36:57.205  Add     2  5 local.                    _afpovertcp._tcp.         Totoro

This is probably why it still appears in the Finder sidebar.

02-May-2010 11:51 PM:
I've also found that turning off AirPort and turning it back on will often fix the problem for a while, but it will eventually return.

20-Dec-2010 01:13 AM John Grigutis:
Since installing the 7.5.2 (75200.14) firmware on my Time Capsule, I haven't experienced this problem. So this issue might have been caused by a bug the the previous 7.4.2 Time Capsule firmware.