What is the state of multicast support in consumer grade routers

Question

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.)?

Answer 1

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.

Answer 2

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.