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Beginner

Routing Multicast (Apple Bonjour Specifically) in Routed/VLAN'd environment

Hi all,

I'm working on a network that is based on a core 3750 stack running IP services IOS (12.2.52 from memory), with a number of edge switches - 3560's running IPBase IOS.

The edge switches are purely layer 2 devices, and the only layer 3 interface on them is for management. Connection back to the 3750 core is via etherchannelled dot1q trunks carrying the endpoint voice, data and that management vlan. Layer 3 interfaces (associated with the relevant vlans) on the core switch serve as the default gateway for all endpoints, and the core performs the inter-vlan routing as such.

We also have a wireless infrastructure with 6 1100 series AP running in lightweight mode being managed by a 4400 series controller. The corporate SSID is associated with a VLAN that is then also trunked back to the core 3750 and is associated with it's own layer 3 interface.

The problem that we are now having is that a number of users have various apple mobile devices (iphones/ipads etc) that they are trying to synch with thier desktop or laptop machines. Typically the apple devices will be connected via wi-fi, and the desktop/laptop will be connected via the edge switches.

I've done a bit of background research and it seems as though the mobile device searches for the laptop/desktop using Apple's 'bonjour' service/protocol and from what I can gather this is a multicast service that uses the address 224.0.0.251.

I believe that the core is enabled for multicast routing, as the global command:

ip multicast-routing distributed

has been added to the config, along with the following command:

ip pim sparse-dense-mode

on all of the layer 3 vlan interfaces that are associated with the endpoint ranges, and corporate wireless SSID.

The 4400 wireless controller has also had 'Ethernet Multicast Mode' set to 'Multicast' with the multicast group address of 224.0.0.251

However, it still seems that the mobile apple device and desktop/laptops cannot find each other.

If anyone on here has got this Apple Bonjour service running in a routed/vlan'd environment I'd be very interested to hear your comments!

Thanks in advance for your comments!

-Gordon

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Guru

Re: Routing Multicast (Apple Bonjour Specifically) in Routed/VLA

Gordon

My understading of 224.0.0.x addresses is that they can only be local to the vlan/subnet and that routers will not forward them across L3 interfaces. So i cannot see how you could get this to work short of having one flat vlan for all apple devices.

Jon

8 REPLIES
Cisco Employee

Re: Routing Multicast (Apple Bonjour Specifically) in Routed/VLA

Hi Gordon,

I'm highly suspicious that apple bonjour sends multicast packets with a TTL=1 given the description:

http://developer.apple.com/networking/bonjour/faq.html

"mDNSResponder is a Bonjour system service that implements Multicast DNS Service Discovery for discovery of services on the local network, and Unicast DNS Service Discovery for discovery of services anywhere in the world."

This can be quickly verified by a wireshark capture on a host PC.

-Andy

Beginner

Re: Routing Multicast (Apple Bonjour Specifically) in Routed/VLA

Hi,

Thanks for the response - I must admit that I had already come across that document in my search for an answer on this, and one of my next steps was to grab a couple of wireshark traces to find out exactly what is going on.

However, from pretty much every document I have read there does not seem to be the definitive answer as to whether it is possible to get an apple mobile device to sync with another device on a different subnet.

Regards,

-Gordon

Hall of Fame Guru

Re: Routing Multicast (Apple Bonjour Specifically) in Routed/VLA

Gordon

My understading of 224.0.0.x addresses is that they can only be local to the vlan/subnet and that routers will not forward them across L3 interfaces. So i cannot see how you could get this to work short of having one flat vlan for all apple devices.

Jon

Beginner

Re: Routing Multicast (Apple Bonjour Specifically) in Routed/VLA

Hi,

Thanks for the feedback - I think that I've pretty muched reached that conclusion.

There seems that there might be a fix for this on the horizon with Apple's Wide Area Bonjour service, but I don't think that's available as yet.

Thanks again for your help.

Enthusiast

Re: Routing Multicast (Apple Bonjour Specifically) in Routed/VLA

Hi,

Was anything found to make this work. We have several Apple TV's and iPhones/iPad on different subnets and would like to use AirPlay.

Thanks.

Cisco Employee

Routing Multicast (Apple Bonjour Specifically) in Routed/VLAN'd

I have this problem and found a solution here:

http://www.cisco.com/en/US/products/hw/wireless/ps4570/products_tech_note09186a0080bb1d7c.shtml

Basically, Bonjour service runs on multicast that is designed to not be routed. You have to set up a linux server on a trunk port that acts as a Bonjour gateway that runs on all the vlans you want to bridge Bonjour messages across.

Beginner

i think someone should try

i think someone should try this and let us know the results

https://deploystudio.wikispaces.com/Multicast+Routing

Beginner

Re: i think someone should try

Definitely do-able. There are two ways, either with or without a Linux box running Avahi.
To make it work without a Linux box the switch(es) and/or router must support multi-cast routing and must be configured correctly. Unlike Apple devices, Cisco multi-cast support for Bonjour is not plug and play despite what a sho run might say on the switch/router multicast routing and sniffing needs to be configured to work if the requirement is for Airplay or Airprint (or any other multi-cast service) to operate across VLAN boundaries.
Airplay has been supported on WLC's since version 7.4 and any switch with IOS 12.2-44 (NOT LAN Lite) or newer supports multicast/IGMP.
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