IFF_MULTICAST under linux

my code traverses the interfaces on a (possibly) multihomed linux box. i
read the IFF_MULTICAST flag of each interface to see if the interface
is multicast capable. the code works fine on five boxes that i tested,
but wouldn't you know the 6th one failed--the flag is not set for this
card, an intel gigabit ether card. i saw a message on the web that
implies the IFF_MULTICAST flag is good under BSD but broken under
linux--or'ing three flags is the proper way to do things on linux (which
three, though?). then i saw another msg that said linux sets this flag
by default and the driver should clear it if the interface is not
multicast capable, this is done when the iface is opened. interestingly,
ignoring the flag for this interface yields proper multicast operation
even though the flag implies that the iface is not multicast capable.
all testing done on fully up2date fedora core 1 machines. any
tips/opinions on this behavior are appreciated.

TIA,
Flash

Flash Fyre <(E-Mail Removed)> wrote:

> My code traverses the interfaces on a (possibly) multihomed linux box.

> The flag is not set for this card, an intel gigabit ether card.

If ifconfig doesn't show MULTICAST for the interface, you might try
using `ifconfig eth0 +multicast', though, as the manual page describes,
this should not normally be neccesary.

--
Cameron Kerr
(E-Mail Removed) : http://nzgeeks.org/cameron/
Empowered by Perl!

Cameron Kerr wrote:
> Flash Fyre <(E-Mail Removed)> wrote:
>
>
>>My code traverses the interfaces on a (possibly) multihomed linux box.
>
>
>>The flag is not set for this card, an intel gigabit ether card.
>
>
> If ifconfig doesn't show MULTICAST for the interface, you might try
> using `ifconfig eth0 +multicast', though, as the manual page describes,
> this should not normally be neccesary.
>

You're right, it doesn't. I tried several more linux boxes today, and so
far just the one dell with the intel gigabit card exhibits this
behavior. Annoying.

---
Flash