UC520 & Apple TV

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Jul 27th, 2009
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I have an Apple TV connected wirelessly to my LAN via the wireless facility in the UC520.

The Apple TV can get onto the iTunes store with no problem, and has received a valid address from the DHCP server.

One of the features of the Apple TV is the ability to browse the iTunes library of and stream from other computers on the LAN.

Unfortunately the Apple TV is unable to browse other computers on the LAN for some reason.

When I do a cold start on the Apple TV I can see it on the network and it can see the iTunes library on other computers.  But after about 2 minutes the connection to the other machine is broken and it drops off the iTunes library.  However the Apple TV is still connected to the LAN and the internet.

The Apple TV uses multi-casting packets across the LAN, and I have seen reports that this could be the cause of the problem.

Could I have suggestions please as to how to diagnose this problem, or even better maybe someone has already fixed this problem?


Damian Halloran.

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Eivind Jonassen Mon, 07/27/2009 - 05:14
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Hi Damian,

I've also had some issue's regarding wireless LAN's and browsing other computers. It's probably a security setting on the LAN or WLAN, or maybe both. Have you tried connecting the computers and apple-TV to a less advanced wireless network?? If you have a old wireless router around, I would recommend testing it on that before getting in to deep on the UC.



Marcos Hernandez Mon, 07/27/2009 - 05:44
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I am not clear if you are using the built in Access Point or the external one. We have some multicast performance limitations with our current AP family. Apple uses Bonjour (which requires L2 multicast) for service discovery:


However, this is just for discovering devices and applications, not for the actual media streaming. You mention this stops working after a while. Does it happen when you are actually streaming video, or when the system is idle?


Damian Halloran Mon, 07/27/2009 - 06:17
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Hi Marcos,

I'm using the built-in wireless.

There doesn't seem to be a consistent point where the connection fails except that it occurs after around two minutes.

It usually occurs when I'm trying to set up or in the middle of streaming from the iTunes computer to the Apple TV.


Damian Halloran Mon, 07/27/2009 - 06:19
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Hi Elvind,

Unfortunately I have only a Cisco 521G and controller available.  Maybe I could disable the wireless in the UC520 and try these.

Thanks for the suggestion.

Marcos Hernandez Mon, 07/27/2009 - 06:22
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Can you please post your configuration? Please remove the passwords.



Marcos Hernandez Mon, 07/27/2009 - 20:37
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Your configuration is very simple and looks OK. You have multicast routing and PIM enabled, IRB is configured correctly and it seems you are getting a DHCP IP too on both the Apple TV and the laptop (since initial communication works).

Can you try to enter this command under interface Dot11Radio0/5/0.1:

no bridge-group 1 block-unknown-source

Let me know if that helps. Also consider re-installing iTunes and Bonjour, and upgrading to the latest version of both.

This could also be a multicast performance issue on our side, but we'll see.



Damian Halloran Mon, 07/27/2009 - 21:25
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Hi Marcos,

Thanks for your help with this.

I tried the command and this was the result:

cellardoor(config)#interface Dot11Radio0/5/0.1

cellardoor(config-subif)#no bridge-group 1 block-unkn

cellardoor(config-subif)#no bridge-group 1 block-unknown-source

no bridge-group 1 block-unknown-source not allowed on Dot11Radio0/5/0 interface

Also the iTunes and Bonjour/zero-conf installation are on a new mac so I don't think that will help.

Thanks again.
Steven Smith Tue, 07/28/2009 - 06:57
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From your config, it appears that you are not running voice.  Is this correct, or did you take that part out of the config?

As has been discussed, there are some limitations on multicast traffic on the UC500.  I would suggest you see what devices are sending multicast traffic (by a sniffer).  If you had multicast moh enabled, I would suggest turning that off.

FlorianCokl Wed, 01/23/2013 - 02:10
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Hello Marcos,

Hello Damian,

I have a UC520, too. I have the exact same issue that multicasts from the wired LAN are not propagated into the bridged WLAN on the same UC520 - not even MOH is working!

@ Marcos:

why would it be necessary to enable multicast-ROUTING??!!

Clearly: in the default configuration of a UC520 the vlan-interface (the L2 for the wired devices) and the dot11radio-interface (the L2 for the wireless devices) are bridged (BRIDGED!!) together via the BVI-interface - since we are therefore 

talking about a Layer 2 Connection between the vlan-interface and the dot11radio-interface why would anybody need ROUTING between these two instances??!! Besides the multicast-address used by Apple is one out of the 224.0.0.X (=Local Network Control Block ->

http://www.iana.org/assignments/multicast-addresses/multicast-addresses.xml) and is not supposed to, or shell I say must not, leave the local subnet - but per default has to be flooded out EVERY port in that same segment it originated!

Lets go back to CCNA-Questions: What is the default behaviour of any bridge (and therefore any switch, too!) when it receives a broadcast or a multicast (since a multicast is equally treated as broadcast) on one of its ports??!! -> FLOODING

Since the address Bonjour utilizes is a 224.0.0.X ( it wouldn't help enabling multicast-routing either - because multicasts with this address aren't supposed for other segements except the one they where originated on. Either Apple offers a way with 224.0.1.X (an Address from the Internetwork Control Block (there are addresses available)) or you somehow manage to install a multicast-proxy with interfaces in all existing VLANs, and that will engage in not only forwarding them but placing itself in, as mediator, too.

Resume: I would expect Cisco to fix this (immediately by now)

If you connect 2 Switches (I will leave the details out on purpose) the multicast originated in the VLAN on 1 of the ports on 1 of the switches will be flooded out on every port in that exact same VLAN on both switches.

Shaun Bender Thu, 03/31/2011 - 20:00
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Using AirPlay on Apple iOS and Apple TV devices.

I've setup:

ip multicast-routing distributed

on a 3560 running IP Services and on the two vlans:

ip pim sparse-dense-mode

I'm able to see the Apple TV devices while on the same subnet, but once I switch to the other subnet, the devices are no longer visible.

Any suggestions?


mcasimirc63 Thu, 03/31/2011 - 20:06
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Most of Apples' advanced features uses Bonjour and I don't think it can properly function if the device is not on the same subnet or same L2 switch.  I ran into a similar issue using plex on a couple mac mini's I have.

FlorianCokl Wed, 01/23/2013 - 02:23
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Hello Marcus,

Bonjour uses a well known multicast-address (that's not Apple proprietary)! The problem here is either the dot11radio interface or the BVI (Bridged Virtual Inteface) - one of them is unable to deal with multicast. Either the dot11radio interface can't handle multicast at all or the the BVI is not working as the name BRIDGE (a L2-Connection) implies - or even both? The guys from Cisco have to answer this question - and provide a fix, too.

Like already mentioned above - there is a total of 3 interfaces involved on a UC520-defaul-configuration for 1 VLAN - since there are 2 VLANs (1 for data, 1 for voice) we have a total of 6 - 3 and 3 belong together. For the physical ports on the front of UC520 there's the VLAN-interface, and for the non-wired devices there's the dot11radio - both are bridged together via a BVI. Take a look at the numbers and you see the "beauty" of it - it would be really beautiful if only it was working.

FlorianCokl Wed, 01/23/2013 - 13:17
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Hello Damian,

since I had the same issue - here's what I did - and I can tell already you're not going to like it.

Yes - I bought a Time Capsule

I have configured it with the same parameters as I did with the dot11Radio on UC520

And configured it to bridge between the WLAN and LAN - and guess what - Yes, it works!

Any Apple-Computer on the LAN or WLAN can see everything that any Apple-Computer anounces on the LAN or WLAN.


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