[Ns-developers] Requesting help for csma promiscuous mode

[craigdo@ee.washington.edu]

> > I think that linux has a number of bits that you can set to 
> enable various
> > promiscuity levels:  RxStation, RxMulticast, RxBroadcast, RxProm.
> 
> Really ? Where did you see that ? The only promiscuous things I know
> about are from "man ifconfig":

Okay, maybe I shouldn't have said linux, I should have said at least one
linux net device driver.  It's from a particular driver implementation (3com
etherlink) I was looking at, where all of the receive promiscuity levels are
broken out nicely corresponding to bits available in the NIC hardware:
3c509.c has the following code:

00744  if (dev->flags&IFF_PROMISC) {
00745    outw(SetRxFilter | RxStation | RxMulticast | RxBroadcast | RxProm,
00746         ioaddr + EL3_CMD);
00747  }
00748  else if (dev->mc_count || (dev->flags&IFF_ALLMULTI)) {
00749    outw(SetRxFilter | RxStation | RxMulticast | RxBroadcast, 
              ioaddr + EL3_CMD);
00750  }
00751  else
00752    outw(SetRxFilter | RxStation | RxBroadcast, ioaddr + EL3_CMD);

dev->flags has the IFF_PROMISC and IFF_ALLMULTI bits and the net device
further breaks them down into MAC address-based possibilities.  This seemed
useful/flexible to me.

> [-]promisc
>     Enable  or  disable  the  promiscuous mode of the interface.  If
>     selected, all packets on the network will  be  received  by  the
>     interface.
> 
> and, looking at the include/linux/netdevice.h header, I see only a
> single promiscuity count, not a mask for different levels (see
> __dev_set_promiscuity in net/core/dev.c)
> 
> There is an "allmulti" mode but that seems orthogonal to promisc mode
> (i.e., send up all multicast packets without filtering)
> 
> > Anyway, I think having devices always in promiscuous mode is weird.
> 
> agreed.
> 
> Mathieu