Q: connecting airport express

Sorry, but your issue has nothing to do with Apple networking ... at least not directly. It is on more related to using AirPlay with the version of iTunes that came with OS X Yosemite. That version was initially 12.4.3.1

You would access AirPlay via the AirPlay icon in the iTunes. See the blue highlighted area in the following image.

However, if the icon is missing, may be network related.

Ok, I believe that you are saying that when you select the AirPlay icon, that only the computer shows up as an AirPlay device and not the AirPort Express ... correct?

Also you are using what appears to be two different bootable drives, each have a different version of OS X, on your Mac Pro. I suppose you are holding down the Option key at startup to invoke the startup manager to choose which drive to boot from ... correct?

Some things to try:

• From System Preferences > Security & Privacy
• Click on the Firewall tab > Firewall Options...
• Verify that the option "Block all incoming connections" is disabled (not checked). While you're at it, if you are running either of the native OS X firewalls or another third-party software firewall on your Mac Pro, temporarily disable them.
• From System Preferences > Displays
• Enable the option: Show mirroring options in the menu bar when available. This should place an AirPlay icon on the OS X menu bar.
• Select the AirPlay icon on the menu bar. Does it now display the AirPort Express as an AirPlay device?

FWIW, I have used some variation of iTunes since OS X Tiger when I first starting dabbling with Macs and have been streaming to multiple AirPlay devices since AirTunes was first introduced. I haven't come across the issue you are experiencing when I crossed over to Yosemite, nor have experienced it with El Capitan nor Sierra.

I am assuming that you do not have another Mac to try this with, but I would also assume that they would not have the issue either ... so it appears to be something with running the Yosemite/iTunes combo on your Mac Pro.

One thought, do you have or use Airfoil as an alternative AirPlay "server" other than iTunes? If so, does it also not able to stream to multiple AirPlay devices? ... or any AirPlay device?

If so, then we need to take a closer look at what may be preventing AirPlay from working properly.

As some background, and forgive me if you are already well versed with how AirPlay works, but the following would be a simplified version (for my sake):

• AirPlay is a family of IP protocols that Apple has implemented to stream various types of media content.
• It is reliant on the following partial list of protocols: mDNS (aka, Bonjour) for discovery, HTTP for photos and video, RTSP for audio, volume control, & metadata, ROAP for streaming, RTP for streaming synchronization, & NTP for clock sync.
• If any one of these protocols are inhibited, some feature of AirPlay may not work.

So based on your description of the problem, the protocol that is used first is Bonjour. It goal is to discover what AirPlay "speakers" are nearby and online. Since your Mac Pro does not appear to even find the AirPort Express, gives me the feeling that Bonjour is having an issue.

Some things to check:

• Double-check that your Mac Pro is not running a software firewall. Again there are two of them that could be that are native to OS X:
  • Application-Layer Firewall - This is disabled by default. It would be enabled via System Preferences > Security & Privacy > Firewall tab > Turn On Firewall. It could also be enabled by using a third-party application like Little Snitch.
  • Packet Filter Firewall - Also disabled by default. You would need to use Terminal commands or a third-party application like Murus to get it running. If enabled its firewall rules will be applied first, followed by those of the application firewall's rules.
• IPv6 setting
  • You will want, as a minimum, to verify that your Mac Pro is configured to use IPv6 Local-link only mode. To do so, go to System Preferences > Network > Wi-Fi or Ethernet (depending on how you connect your Mac Pro to the network) > Advanced > TCP/IP tab > Configure IPv6: Link-local only

Ah just a young'in.

No, the install should not have enabled any software firewalls.

OS X Yosemite did introduce issues with network device discovery though by replacing mDNSResponder with discoveryd. It was subsequently added back in El Capitan after numerous complaints. Both are multicast DNS discovery services.

In our case, among the things that dDNSResponder did for AirPlay was providing Bonjour service advertisement and discovery. For the Express, it's used to announce that it is available for AirPlay; For iTunes, it's used to find the AirPlay-ready Express.

It's a stretch, but maybe this is the core reason for what you are seeing here.

There is a way to restore mDNSResponder on Yosemite, but it is not for the faint of heart, as the process does offer the risk of disabling the currently installed OS ... so I do not recommend it.

Can the version of Photoshop CC, you are referring to, work on El Capitan?

Yikes! Then you can certainly forget everything I mentioned in the previous reply.

At this point, the only area I can think of is to verify that your Mac Pro, running from the El Capitan drive, can actually access the Express.

The simplest way to do so is to use the Ping command in Terminal. You would just need to know the IP address of the Express.

To get that, you would use the AirPort Utility, as follows:

• Run the AirPort Utility (located in the Utilities folder).
• Select the AirPort Express.
• In the pop-up window, look at the value after LAN IP address. If it is the only router in your current network configuration is should be: 10.0.1.1.
• You can exist the utility.

On to Terminal

• Run the Terminal Utility (also in the Utilities folder)
• Enter the following at the command prompt: ping -c 3 <the IP address you found above>. Example: ping -c 3 10.0.1.1
• Exit Terminal by entering: exit <return>, and then, quit the application from the OS X menu bar.
• If the results had 0% packet loss then all is good. Anything else would indicate that the Mac Pro is having difficulty finding the base station.

Hello Hugo. Thanks for jumping in to assist.

If the AirPort Utility is not finding the Express, then we need to figure out why before we can tackle the AirPlay issue.

The idea of the ping is to see if OS X, itself, can "see" the base station. This is really no different than the UNIX world as OS X is based on it.

With OS X we can perform pings either directly from the terminal or through a graphical interface. I am going to assume you will prefer to work in Terminal.

I did provide some minimal background on how AirPlay works, but I'd be happy to provide more details if you need it.

However, it appears that we need to work out why the base station is not "seen" from his Mac Pro when running under El Capitan.

So if you can run the ping test I mentioned we can get started. The other thing that would be helpful is to understand his exact network configuration. That is, what is the make & model of each of his networking hardware and how are they connected (wireless, wired, or some combination of both). Is the Express solely for AirPlay streaming? If so, is it configured just as a wireless client (join a wireless network) or for extending another Apple router (extend a wireless network)?