HowTo: Fix printer offline problem by disabling IGMP Snooping on Plusnet Technicolor TG582n router

[#1]

I have been having a problem with my Brother printer. It's connected via a wired ethernet connection, but it kept going offline about 5 minutes after booting and needing to be rebooted before it could be used again.
After speaking at great length to Brother tech support, and running various tests, we concluded it's the Plusnet Technicolor TG582n router that's messing with the Bonjour services that the printer sends to advertise its services. Apparently Bonjour uses multicast to operate, and the router was interfering with that in some way.

[Answer] The fix is to telnet into the Command Line Interface (CLI) of the Technicolor router and disable IGMP snooping completely.  The printer (after a reboot) has now been working fine for over 24 hours.

Supplementary Question: What problems am I likely to see as a result of disabling IGMP Snooping?

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For those who might need to reproduce the fix, I include it here as the CLI is not for the faint hearted at 864 pages!
Telnet into the Technicolor as 'admin':

{admin}=>eth bridge igmpsnooping

{admin}[eth bridge igmpsnooping]=>config
Bridge StateEnabled FloodReports FloodMCasts QueryTo IP
-------------------------------- ------------ ------------ ----------- ------- --
bridge Enabled Disabled Disabled 140 10.0.0.138

{admin}[eth bridge igmpsnooping]=>config state=disabled

{admin}[eth bridge igmpsnooping]=>config
Bridge StateEnabled FloodReports FloodMCasts QueryTo IP
-------------------------------- ------------ ------------ ----------- ------- --
bridge Disabled Disabled Disabled 140 10.0.0.138

Check that that is doing what you want it to. If all OK, then

:saveall

to save the configuration

BTW: Tips on the CLI:

You can issue an entire command in one line, or navigate through the configuration hierarchy one command at a time.
‘:’ takes you back up to the top level
‘help’ is context sensitive in any hierarchy position
Prefixing a command with ‘:’ issues it as if you were at the top of the hierarchy.
Values are fed in using the pattern ‘[setting]=[value]’ 

The default Bridge is called, ermmm... 'bridge' !

I attach a copy of the CLI that I found. No guarantees as to how up-to-date it is.

PS: minus several million points to Plusnet support who, after a wait of 45 minutes to get through to their chat, told me they don't support 3rd party devices, and when pointed out that the Technicolor was their device (and that its manufacturer, Thomson, expect the ISPs to do all the support for it) told me that they just do basic setup and that anything more complicated than that should be posted to the forums (compared to Brother who spent several hours working through the problem with me).

[#2]

According to https://en.wikipedia.org/wiki/IGMP_snooping is something for network switches that blocks some multicast packets on the switch. So it can do no harm to not block anything.

So I foresee no problems...

[#3]

told me that they just do basic setup and that anything more complicated than that should be posted to the forums

So PN must be employing non tech staff now   to difficult so you have to ask here LOL

[#4]

IGMP Snooping is a technique that limits which ports the router sends received multicast packets to.It restricts the packets to ports that have requested them.

If you subscribe to BTTV, then with snooping off when you watch an internet TV channel each received multicast TV packet will be sent to every device on the local network.Not a big problem with a Gigabit wired network but it will probably saturate your wireless network and make it unusable while you are watching TV.

You have put me off Brother printers.

[#5]

Why do BT use multicasting on a home router when there is almost certainly only one TV as a destination?

[#6]

Because it minimises the load on the wide area network - which is the main reason for multicasting.

As everyone who is watching a specific TV channel at a specific time needs to get the same stream of IP packet, BT's servers send the packets out once, and it gets distributed by the wide area network to any and all the home routers that have requested  that particular stream (all the intermediate routers do something similar to IGMP snooping).

Multicast packets have no "to" address - in that sense they are like junk mail delivered by the postman, but junk mail where the sender sends it once, and each stage of the distribution process duplicates enough copies to pass on. 

When the packet arrives at your home  it is up to your router to decide which devices on your local network get the multicast packets. With IGMP snooping enabled, the router knows who has asked for a particular multicast stream and only sends it there. Without snooping the router sends the multicast packets to all the devices on your network. Those that don't want them simply discard them.

Hence it's not a big issue if your LAN is significantly faster than your Broadband link. However with a slowest wireless LAN it can easily saturate the capacity.

iPlayer and its ilk work differently as each packet is individually addressed.

[#7]

Thanks wisty, that's what I had kind of assumed, but with the new information about which consumer services use multicast and the likely problems with the wireless / broadband bandwidth ratios.

This isn't an immediate problem for me as I don't use BT or any other live streaming services.

However, to me this looks like an issue with the IGMP implementation in the Technicolor. I see that there are no real standards for IGMP (it falls between the router and multicast committees).

Does anyone have a better solution than just switching off IGMP completely?

I did configure the router to have a device profile for the Brother to be a 'Printer' rather than a Generic Device, but that didn't make any difference, although maybe I needed to reset the IGMP groups after doing that.

Thoughts anyone?

[#8]

If you subscribe to BTTV, then with snooping off when you watch an internet TV channel each received multicast TV packet will be sent to every device on the local network.Not a big problem with a Gigabit wired network but it will probably saturate your wireless network and make it unusable while you are watching TV.

You have put me off Brother printers.

In footballing terms, that was an answer of two halves... thanks for the first bit.

As for putting you off Brother printers, that's just nonsense. The Bonjour services that the Brother printer uses are the ones that Apple use for AirPrint, so maybe they're all wrong too.

And Bonjour is Apple's implementation of ZeroConf - https://en.wikipedia.org/wiki/Zero-configuration_networking - an automatic network configuration system that, among other things, allows autodiscovery of services. So multicast is important in many other areas than just streaming TV.

Also, since I switched off IGMP, I've found that the controller app for my Logitech Squeezeboxes has suddenly found all the devices, something that it hasn't done for ages.

The balance of probability points towards the Technicolor's implementation of IGMP being a bit flakey...

[#9]

"CUPS is the standards-based, open source printing system developed by Apple Inc. for macOS^® and other UNIX^®-like operating systems. CUPS uses the Internet Printing Protocol (IPP) to support printing to local and network printers."

So all Linux (and Unix like) printers use the Common Unix Printing System. So the problem isn't related to Brother printers - any printer would behave in the same way. Perhaps you need a router or switch that can filter multicast packets by sub-area network?

[#10]

Well, one thing that I did notice was that each ethernet port has its own IGMP enabled state.

Given that the printer is the only device on one port, I did wonder about disabling just IGMP on that port, but I wasn't certain if it disables snooping on traffic to that port or from it. Only one way to find out, I guess...

[Actually, the other reason I didn't do that is that when I tried to investigate, the CLI kept requiring a parameter name for the Bridge to be configured. Tried lots of things and nothing worked. Didn't figure out until later that the default Bridge for the Technicolor is called 'bridge' ]