Some Bonjour printers not found by iPad

Question

We are using iPads on our service drive and want to print to several HP M608 and M553 printers. When printing from an iPad or iPhone, Bonjour is finding a number of printers on the network but of the six printers on the drive, only ONE (an M553) is appearing in the list of available printers. I have confirmed that Bonjour is turned ON on all of the printers and DNS is set correctly. There are three M608 printers and many M553 printers showing up from other departments that are on the same network but not the printers we need. We can print to them through CDK on the iPad and other attached Windows computers, and can ping and access them through http/s -- it's only the Apple devices that are not detecting them.

• The iPads are connected to a different VLAN than the printers via wireless.
• The printers are ALL on the SAME VLAN but not the VLAN the iPads are on.
• Firmware is up-to-date.
• iOS is up-to-date.

Answer 1

As @trcm mentioned, typical Bonjour service advertisements are multicast in a way that is not intended to cross routers, so since your printers are on a different VLAN than your iPads, it's no surprise they're not being discovered via Bonjour.

They cases where some printers ARE being discovered might be explained by wireless peer-to-peer protocols, or maybe all the printers that are being discovered are actually on the same VLAN as the iPads after all.

There have been a number of protocols over the years that have attempted to allow Wi-Fi devices that are within Wi-Fi radio range of each other to discover and talk to each other even if they don't have proper connectivity to each other through some kind of infrastructure WLAN or LAN. One of those was Wi-Fi Direct, which Apple never adopted and which was generally considered a marketplace failure, and has since been replaced by Wi-Fi Aware, which looks like it might be heading down the same path. Another is Apple's own AWDL (Apple Wireless Direct Link), which was an optional part of AirPrint support. AirPrint is the technology that allows iPads and iPhones to print without installing any printer drivers. Despite the name, it doesn't require Wi-Fi per se, and it doesn't require AWDL.

Looking at the spec sheets for your two models of HP printers, it looks like both models support Wi-Fi Direct, but only the M553 supports AirPrint. I'm guessing the M553 also supports AirPrint-over-AWDL, which is why you're able to see that one M553 when you're in radio range of it. Either that, or that one M553 is actually on the same VLAN as the iPads after all. Maybe someone joined it to the wrong Wi-Fi network, or maybe the Ethernet switch port it connects to is configured for the wrong VLAN.

Answer 2

Bonjour advertisements (multicast) don't want to travel across VLANs by default, but you have a few options :

• Ask your network admin to setup multicast routing, if it's Cisco kit look into 'Rendezvous Points'.

or

• Setup Unicast DNS Service Discovery, this will mean adding appropriate records to your local DNS. It will be complex, and you probably don't want to pick this option, but the iPads would then see the Bonjour services from the printers automatically.

or

• Using an existing Mac on the same network as the printers to advertise across both your VLANS: Manually install all your network printers on the Mac using their IP addresses and then share them. Ensure the switch port for this Mac is set to Trunking mode in order to allow access to all VLANs, then using the Manage Virtual Interfaces option under Network, add the wireless network’s VLAN, finally assigned the Mac a static IP on the wireless VLAN.