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UPDATED with some corrections and additional facts July 17, 2016. The Access Point is a Linksys E2500, not a Netgear as originally stated. I also tried to be more clear and explicit about what works. We do not need mDNS on the "outer network." We just need it to continue working on the "inner network" (published by the Access Point).

Hard to explain in the title. This question might straddle the line between Stack Overflow and Super User. But I will start here on SU.

TL;DR We have a WiFi Access Point. It publishes an SSID and machines and IoT devices connect to it. When it is standalone (not plugged in to any external network), all machines connect and mDNS/Bonjour resolves. But when we plug our access point into an outer host network, mDNS stops resolving, though machines can still connect to AP using SSID. Worth noting the machines can also reach a file server on the outer network. Only thing broken is mDNS can no longer resolve mDNS on the AP's local network. There is no need to resolve mDNS on the outer network. Read on for details.

More detail:

We have a Linksys E2500 access point (AP). The Linksys AP publish an SSID and machines are able to connect to it.

A couple of facts to assert:

  • AP is installed in factory in China
  • Linux, OSX, and Windows computers connect over WiFi
  • Our product is an IoT device that connects over WiFi using mDNS (aka Bonjour/zeroconf...)
  • On all other networks we have tested mDNS works correctly to resolve host name
  • I have no way to connect remotely from the US to this network

Now consider the following two cases. In the first case products that use mDNS (aka Bonjour) work but in the second case mDNS does not resolve the name to the proper IP address:

  1. mDNS resolves correctly

    Access point is configured with DHCP enabled. Access point is stand alone, meaning it is not plugged in to a host network. There is no access to the Internet or any other LAN. Most settings are set to AP's default. mDNS resolves the host name of our product to the actual IP address. All machines can connect to the AP either via the SSID or via Ethernet to the ports on the AP.

  2. mDNS does not resolve

    Access point has DHCP disabled. Access point is plugged into an Ethernet port providing access to factory's network. Let's call the factory host network the "outer network." The outer network provides DHCP services. mDNS is unable to resolve host name to IP address. We tried both with DHCP enabled on AP and disabled. We have not yet changed any other settings on AP.

In other words, everything works on the AP as expected except when we plug an Ethernet to the "outer network". We are not trying to resolve mDNS on the outer network. It's still all the local LAN related to the AP that needs to resolve the mDNS names. The only purpose of plugging this in to the outer network is the Linux and Windows machines need to talk to a file server on the outer network. This works. The only thing that breaks is mDNS.

I presume this is some kind of subnet problem. It may be impossible to diagnose without much more info. I am hoping someone reads this and goes "AHA! I know what is happening."

As far as I can tell, this model Linksys E2500 does not have Bridge Mode. It has been suggested that perhaps Bridge mode could be the best setup here. I am not clear on why that might be but I am willing to try it.

I plan to bring a Wireless Router with when I go to factory in next week. I am leaning towards a product like Linksys WRT1900AC. If anyone can recommend a different product in the < $250 range please speak up. Would like one with support for AP or Bridge mode. Dual band is nice but not strictly needed. I do not need a fancy enterprise product. The range is short and the conditions constant.

I'm not an IT person but I do manage IT people. My IT people did not set this system up. It was setup in China. I am going out there since I need to unblock this and complete several downstream tasks.

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  • Is this just a single AP, and is it the only AP publishing this network name (SSID)? Which port of the AP (WAN vs LAN) are you plugging into the external network? When you "enable DHCP" are you enabling NAT at the same time? When you do that, do you switch to using the WAN port?
    – Spiff
    Commented Jul 8, 2016 at 17:49
  • Are you sure the only difference is whether DHCP is enabled or not and whether it's plugged into the factory's network or not? No other changes to the AP configuration are being made? And it would probably help to know the make and model of the "access point". If it's actually a typical home wireless router being used as an access point, there are a lot of broken settings that can cause it not to act as a bridge.
    – David Schwartz
    Commented Jul 8, 2016 at 19:47
  • To the two comments above: There is just this one single AP on this network. When it is standing alone without having any other "outer networks", mDNS works. BTW, in all cases computers can connect to WiFi. It is only mDNS that breaks. I have to check which port they are plugging into in back. Frank's answer addresses that. David: not sure. the only button we are changing is the dhcp enabled or not. But I am not there so I can't swear to this. I am going to try Frank's advice and try bridge mode. Thanks guys!
    – Rich Sadowsky
    Commented Jul 9, 2016 at 20:10

1 Answer 1

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THe fact that your AP has a DHCP mode tells me that it's probably an AP/ROUTER and not just a simple AP. If you wish to connect to your "outer network" you should do so with your AP in BRIDGE MODE so there is no FIREWALL/PACKET-FILTERING.

If your AP/ROUTER does not have a BRIDGE MODE, to get around this you can disable DHCP on the AP, but you will have to plug the "outer network" into a standard switch port on the back of the AP/ROUTER, NOT the WAN/INTERNET port(which has a firewall/packet-filtering which cannot be disabled by a BRIDGE-MODE).

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  • Sounds like excellent advice. We will give that a try. What's interesting is we test constantly with dozens of different Access Points and routers and hadn't encountered this. But your advice sounds like something to try. It's the weekend now where the AP/router is installed so we will try this solution Sunday night/Monday morning. Thanks! Will mark correct if this does the trick.
    – Rich Sadowsky
    Commented Jul 8, 2016 at 19:14
  • This answer would only address why mDNS might not be getting to the outer network. But was that OP's problem? I thought OP's problem was that mDNS stopped working even between wireless clients of the AP.
    – Spiff
    Commented Jul 8, 2016 at 19:30
  • @Spiff, I do this for a living. When I walk into a new client's shop, they usually want me to reuse existing equipment when redesigning their IT infrastructure. Many have existing AP/Routers configured in a way that prevents them from seeing many network devices due to the lack of a bridge mode. In most cases, I remedy that by disabling DHCP on the unit and plugging in the network cable to the switch side of the AP/Router. This disables all packet-filtering and allows the AP to actually be on the same LAN as the local network, not some subnet.
    – Frank Barcenas
    Commented Jul 8, 2016 at 21:59
  • @Spiff, to your question, I am not trying to use mDNS on the outer network. The need for mDNS/Bonjour[/zeroConf] to resolve is between the machines either connected wirelessly or plugged in to the our AP. When not plugged in to the outer network, mDNS resolves fine and our IoT device and the Linux and Windows machines all communicate with each other. They are connected to the SSID of our AP or wired and plugged into the ports on same AP. When they plug that AP into the outer network machines still connect wirelessly and can talk to outer network machines, but mDNS no longer resolves.
    – Rich Sadowsky
    Commented Jul 17, 2016 at 22:52
  • Guys reading your answers and comments, and reading back the info I just updated, I'm convinced they are doing something wrong at the facility. Reading Frank's answer again if they followed all of my instructions they would have tried exactly what you say in the second paragraph. I am most likely going to stop attempting to debug this remotely since in about a week I will be at the factory. I'll bring two new Wireless Routers with enough bells and whistles that I should be able to try just about any configuration. Thanks for the replies and I will update you when I finally resolve this.
    – Rich Sadowsky
    Commented Jul 18, 2016 at 0:48

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