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I am designing a system which has multiple small embedded systems hosts communicating in a LAN. UDP multicast fits nicely for my purpose.

But I am worried about multicast support in commonplace routers. I need to deploy the system to normal households equipped with a Wifi router, so I could encounter any kind of routers. I will use UDP broadcast if multicast will be more trouble than benefit.

To decide, I am thankful for any data or experience on multicast support in today's commonplace routers:

  • Do all consumer routers sold today support multicast reasonably? Limitation to LAN is not an issue for me, I do not need multicast across the Internet.
  • How about older routers?
  • Are there any big issues in commonplace multicast implementations I need to be aware of (e.g. packet drops, configuration issues, etc.)?
henning77
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  • I only ever tried it on business grade - see catalyst - switches. There it required configuration. Never even tried on consumer grade. I just assumed it wouldn't work. – RobotHumans Jan 11 '15 at 07:17

3 Answers3

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Are you talking switches or routers? In a consumer setting I suspect switches. My experience is that they all support multicast, though not at wire speed. Also the cheap ones tend to broadcast any multicast traffic to all ports (no IGMP snooping). Packet loss is definitely something you need to deal with, it can and will happen even on 'professional' networking gear.

Edit: as long as you are in switched network, you typically don't need to configure anything.

eile
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  • Home and small office routers mostly. These types which have integrated Wifi, a broadband line, and mostly four ethernet ports. I might encounter more sophisticated gear occasionally though. Would that make a difference for multicasting? – henning77 Feb 22 '12 at 19:18
  • From your questions it seems to me that you want to stay in the LAN, which means that you're likely dealing with a switched network (all IP addresses are in the same subnet). Multicast routing would be another can of worms you probably don't want to open. – eile Feb 23 '12 at 19:00
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In worst case scenarios, when the routers don't allow multicast traffic, I would encapsulate the multicast packets into a unicast IP address. This way the routers would handle them as normal unicast data. You might want to check mrouted .

Good luck

H_squared
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In many scenarios the equipment either does not support IGMP spoofing, or it is off by default. There are two problems:

  • Any wireless interface can be saturated by the traffic.

  • Poorly configured units may inadvertently route traffic out the default gateway stalling legitimate traffic.

In either case, you will have your equipment discarded as the cost of investigation will almost certainly outweigh the benefit received.

If your traffic has a limited rate and you are not concerned about the WiFi impact, you could use the local broadcast address to ensure delivery to recipients, without impacting on the routed communications.

You could install a discovery mechanism into your nodes it may be worthwhile to implement a unicast overlay to ensure that traffic does not have inadvertent impact.

A single larger group of customers with some non-compliant devices requesting support will swamp any costs associated with development or additional traffic caused by not implementing true multicasting.

Pekka
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