Am Mittwoch, 31. Januar 2007 17:24 schrieb Waldemar Brodkorb:
[...]

> Hmm, promiscous mode is definetely working, otherwise tcpdump on my
> routers wouldn't get any packages. 

that's not true. If you use tcpdump without passing an interface (or by using 
the "all" interface, or by passing the "-p" option) then tcpdump will NOT set 
your interface in promisc mode.

Promisc mode is not needed to capture packets that have the arp/mac address of 
your interface (or the broadcast mac) as destination on layer 2. The target 
ip address is not important here at all, because capturing/addressing and all 
this magic stuff is done in layer2 in ethernets and without promisc mode the 
network card/driver will not pass any packets to the kernel that have a 
foreign arp/mac as destination.

Ahm, what I wanted to tell you??? ah, I just wanted to point out that a 
working tcpdump is no evidence of a working promisc mode.

there a a few (but really only very old) network cards, where you will get 
problems with promisc mode, because of the driver or even the hardware 
doesn't support this.

> Why you need to set excplicetely 
> the promiscous mode? Normally the application, like tcpdump, kismet
> and brctl are doing the right thing for you.

that's the important point here. the simple fact that briding works shows that 
promisc mode must be functional on freewrt routers. briding without promisc 
mode will not work correctly. My own setup bridges wlan and lan and I haven't 
a problem with that at all... Oh wait, I have a problem with my setup, but I 
think it's a bit too spaced out to mix that up with the problem discussed in 
this thread... My problem seems to be more related to masq, wlan and lan 
briding + routing packets over my lan twice before it gets tunneled via a vpn 
connection. But it's too complicated and strage to tell you the exact facts 
briefly, so I will report that sometimes later. :)

But in generell a bridge needs to pass each packet to the other side(s) of the 
bridge, even if it hasn't the local interface mac address as destination, so 
promisc mode is definitly needed for a working bridge.

bye,
 Ralph
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