How Apple’s Bonjour Networking Standard Affects Installs

Bjørn Jensen 327 Views

Apple devices have become a major part of anything done on the network today, whether it’s for home or for business. Most businesses, however, do not normally incorporate Apple networking devices into their offerings, aside from the BYOD (Bring Your Own Device) sort of products like iPhones and tablets. Unlike in a home where things such as direct streaming to Apple TVs, printing via Airprint, Airport Express for audio distribution are used frequently, businesses don’t tend to implement these types of things. Until now.

Some businesses are making use of low-cost alternatives to products offered in their own environments. For example, schools have started incorporating Apple TVs into classrooms so teachers can instantly stream what’s on their tablet to the big screen. This is an excellent use of technology that makes a solution that would have normally taken some pretty expensive gear cost a fraction of the price. The issue is that teachers would also like students to be able to stream their devices to the big screen.

Under normal circumstances in a school, the student’s networks are segmented onto another VLAN/subnet that cannot access the teacher’s network. This is done, of course, to keep students from accessing sensitive information like tests, records, etc. How then can one give access to another network? Normally this is done via Inter-VLAN routing. It would normally be easy to put the routing rules in place that would allow students access only to the Apple devices they’re trying to stream to. However, Apple TVs are not made for schools or businesses or any other network that requires VLAN’s or network segmentation.

Why am I talking about businesses and schools on a consumer-centric website? Well, when one starts building larger networks for larger homes with hundreds of networking devices, one also has to treat it like a larger business network. In other words you’re going to be segmenting the network into numerous broadcast domains with VLANs. Why is this relevant to streaming to Apple TVs? As I said earlier, Apple devices are made for the home and not for business networks.

Inside Apple’s Bonjour Networking Standard

To understand why this is a problem, one has to understand how Apple implemented its broadcast discovery protocol, Bonjour. This is Apple’s proprietary Zero Configuration (Zeroconf) networking service that includes service discovery, host-name resolution and address assignment. Like any broadcast, this protocol sends messages out to every device on its local network to determine which devices it can speak to.

For Apple, this is like someone yelling in a room, “Hey, is anybody in here that can talk to me in Apple speak?” Then the devices that can will reply, “I’m here and this is my name and IP address.” Then it uses multicast and multicast Domain Name System (mDNS) to do whatever it needs to do. Multicast allows a device to send lots of duplicate information to many devices concurrently, unlike Unicast, which is how most devices talk to one another. mDNS service records allow the devices to keep tabs via device names instead of IP addresses in the event a device acquires a new IP.

Now that we understand what Bonjour is, we need to speak about one of its biggest limitations and why it cannot, under normal circumstances, traverse subnets. When Apple implemented Bonjour, it never envisioned this would be used outside of a small home environment. To keep things simple, Apple implemented Bonjour as a “link local” protocol with a TTL (Time To Live) of 1. A TTL essentially tells a router whether or not to discard a packet so it doesn’t get continuously forwarded on.

The TTL works like this: A router is required to subtract at least one count from the TTL field. Once it reaches 0, it discards the packet and sends a message back to the sender so they know whether or not they need to resend or not. So if Bonjour has a TTL of 1 when it reaches the router, or equivalent Layer 3 interface, the router will strip one count off of the Bonjour packet’s TTL, leaving it at 0 where the router then discards the packet. This means Bonjour is essentially limited to speaking to devices within its own network and is not meant to be able to cross any Layer 3 interfaces by design.

Manufacturers to the Rescue

Must we always leave all Apple devices on the same subnet as the homeowner’s iPads, iPhones, etc.? What if we have a large home with numerous streaming devices just bringing down the network with excessive broadcasts and multicasts? Luckily, numerous manufacturers have stepped up to the plate to create an answer to our dilemma. One of which is one of my favorite companies, Ruckus Wireless.

By the middle of 2014 most enterprise-grade networks will have adjusted to life with Apple and created ways around the aforementioned issues. Ruckus is set to incorporate “SmartWay” technology into its 9.7 firmware before the end of 2013 that works as a bridge between the networks so mDNS requests are forwarded onto another network. Normally this is very chatty, but Ruckus has devised a solution where unnecessary traffic is prevented from being forwarded on. Unlike other manufacturers that will just forward all Bonjour requests across subnets, SmartWay offers granular control of the services one wants to forward. This is good because in WiFi implementations, multicast and broadcast don’t behave the same as they do on a hard wire.

When access points transmit broadcast or multicast frames, they do so at a very low data rate to ensure the frames are delivered to every receiving device. This means traffic is slowed down a lot more and takes up more airtime than a unicast frame of the same size. This is why Ruckus wants to limit the amount of broadcast and multicast traffic moving across subnets by giving such granular control over the SmartWay bridge.

In a world where Apple is ubiquitous, manufacturers and vendors must quickly adapt around the products used by the consumer. It’s interesting to see a company that focuses so much on the home and end user able to force companies to make drastic changes to their software and/or hardware to stay relevant. If you’re implementing commercial-grade networks with VLANs, then you too will have to adapt quickly and adopt some form of networking gear that allows you to bridge Bonjour to another network. That is, until Apple finally decides it’s ready to get out of the home and into the corporate world. For us, we will be testing and implementing the SmartWay bridge into our networks hopefully by the end of 2013, ready for the new year.

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