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Re: Why does sending multicast UDP require a gateway?
- From: Andrew Lunn <andrew at lunn dot ch>
- To: Grant Edwards <grant dot b dot edwards at gmail dot com>
- Cc: ecos-discuss at sources dot redhat dot com
- Date: Wed, 30 Mar 2011 07:53:32 +0200
- Subject: Re: [ECOS] Why does sending multicast UDP require a gateway?
- References: <imtmn5$n3f$1@dough.gmane.org>
On Tue, Mar 29, 2011 at 10:33:09PM +0000, Grant Edwards wrote:
> Somebody I work with has spent the last three days trying to send UDP
> multicast packets using eCos and the FreeBSD network stack.
>
> After quite a bit of trial-and-error we've discovered that you can't
> send UDP multicast packets without configuring a valid gateway
> address.
>
> That seems broken to me.
>
> What are you supposed to do if you're on a strictly local network that
> doesn't _have_ a gateway? [That is the case for many of our products.]
Hi Grant
In the Linux world you have to do something like:
ip route add 224.0.0.0/4 dev eth0
before multicast works. The kernel has no idea which interface to send
the multicast packet out, unless you add a route like this. Maybe in
the BSD world, instead of defining the interface directly, you give
the local IP address on the interface?
Maybe this helps:
http://www.freebsd.org/doc/handbook/network-routing.html
In the example routing table is:
224 link#1 UC 0 0
Andrew
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