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Breaking Subnet Boundaries with Bonjour: Simplifying Apple TV and AirPlay in the enterprise

On February 12, I announced on Twitter  that I was shooting video for Aerohive’s second video blog. Part of the reason I was cryptic about the subject is that the video is supporting today’s announcement of Aerohive’s new Bonjour Gateway, a BYOD feature that makes advertised services available throughout the entire layer-3 network.

Why is this so special?

1.  Plug-and-Play. Bonjour is built on multicast DNS (mDNS), a link-local multicast protocol that, by definition, is confined to a single network link. It does a great job advertising services on the local broadcast link. That’s why your single-subnet home Apple network is so easy to use: the printer says hello, the Apple TV says hello, the AirPort says hello, and you don’t need to know a darn thing about IP addresses to configure and use everything.

In a network of any size at all – by which I mean a network with more than one subnet – the link-layer multicast foundation keeps you from learning about services that aren’t on your VLAN. Our Bonjour gateway allows for controlled advertisement of services across router boundaries.

In designing this feature, we wanted to preserve the plug-and-play nature of Bonjour. We wanted our customers to be able to flip a switch and see services throughout the network. We specifically did NOT want our customers to have to learn a lot about the Bonjour protocol design, how to route and flood multicast frames, and think carefully about how to replicate multicast traffic between VLANs or smoosh devices together on to one Bonjour super-VLAN.

2.  Flexibility. One possible solution that we discarded pretty quickly was flooding multicast frames willy-nilly across the network. Yes, you can flood multicast DNS frames everywhere.  However, if you have two networks – for simplicity, let’s call them “employees” and “visitors” – you may want to have services on both networks. Printers may be on the employee network, and an Apple TV in the customer briefing center may be on the visitor network. If you want visitors to print and employees to use AirPlay to screen mirror in the customer briefing center, you need to pass Bonjour advertisements both ways across the subnet boundary. If your only tool is flooding multicast frames, you can only do this by creating a routing loop. By understanding the protocol, you can easily advertise services in both directions.

3.  Efficiency. If the network is segmented into VLANs or subnets for scalability purposes, you are defeating that design goal by flooding multicasts. Plus, there’s some subtlety in the way that Bonjour advertisements are sent in response to queries, so simply replicating the multicast frames isn’t enough. By the time you build enough intelligence into your multicast forwarding, you’ll wind up with something that looks a lot like our protocol-level engine.

Bonjour services consist of a service name plus a type (and a domain, which isn’t commonly used with mDNS Bonjour). Both are expressed as strings. Because our Bonjour Gateway understands the protocol format, we can do string matching to filter services that are re-advertised. You can choose to share all printers, or perhaps share only the Apple TV in the customer briefing center. I don’t know what services are important to you, which is why we built the feature so that you can define the services that are important enough to share with the rest of the network.

4.  Multi-vendor. Our new Bonjour Gateway was designed to work with any network, whether you use Aerohive APs for Wi-Fi or not. Although we would obviously like you to use an all-Aerohive network, it’s possible to use the feature on networks that use other wireless equipment. Bonjour limitations are networking problems, and fixing networking problems requires networking expertise. 

Part of the reason that it plays well with others is that we’re solving a networking problem with a network device. It fits naturally as a new feature in HiveOS, and therefore, we’re delivering it at no charge as we always do with software updates.

Where’s the video?

If you’re reading the Aerohive blog, I’m going to assume that you’re here because you want more than what was in the official announcement. (A special hello here to all Wireless Field Day attendees!) That’s why this blog entry features the “demonstrator’s cut” video from our announcement, where I show off the feature in a single take. At 15 minutes, it is significantly longer than the regular video, but it has all the background you should need. As with the official video, I’m using AirPlay as my demonstration tool. AirPlay works fine across a router, but you can only discover it exists by listening for Bonjour advertisement. Once that discovery is enabled, AirPlay works like a treat, as you can see in Aerohive Video Blog, embedded below.


 

 

This is a major piece of technology for us, so in the next blog I’ll talk more about how filtering works. If there’s something you want to know more about, please leave a comment.
 



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