[realtek] Multicast filtering

[Donald Becker]

On Thu, 30 May 2002, Karthik Thirumalai wrote:

> I am running redhat 7.x and using the rtl8139 driver which came in the
> package.

Are you using 'rtl8139' or the '8139too' driver?
What is the version number of the driver?

> I am having trouble with the multicast filtering. My card does not seem do
> any filtering (i check this with a tcpdump). The scyld website says that
> 8139 supports multicast filtering.

It does, using a 64 bin filter based on the upper six bits of the
Ethernet CRC.

The 'rtl8139' driver uses this hardware to filter multicast reception.
The only user-tunable setting is a module parameter named
'multicast_filter_limit' with a default value of 32.  The driver
switches to rx-all-multicast mode when more than 32 hardware multicast
addresses are accepted.  This avoids the driver recomputing and
reloading the filter with a large (and presumably frequently-changing)
multicast-accept list.

The '8139too' driver started from my driver code, but I don't track what
changes are made to it.

> My recv uses 225.0.0.37 port 6400.

Keep in mind that IP multicast addresses are over-mapped to Ethernet
multicast addresses.  Multiple IP multicast addresses end up on a single
Ethernet multicast address.  (Grrrr, all for political/control reasons.
With 47 bits it wasn't like there was a shortage of Ethernet address bits.)


-- 
Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
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