On Feb 23, 2012, at 5:58 PM, Michael Richardson wrote:
>
>>>>>> "Paul" == Paul Sheer <paulsh...@gmail.com> writes:
> Paul> Actually I found the answer to this, as below.
>
> Paul> Would anyone consider adding this support to libpcap: i.e. a
> Paul> new member within pcap_opt ?
>
> I think that it should probably just be on.
> Principal of least surprise.
Here's why PACKET_MR_ALLMULTI is currently *not* turned on:
https://sourceforge.net/tracker/?func=detail&aid=599857&group_id=53067&atid=469577
> On Redhat Linux 7.3 with:
> kernel-2.4.18-10
> ethereal-0.9.4-0.7.3.0
> tcpdump-3.6.2-12
> libpcap-0.6.2-12
> (and the same behavior observed also with
> tcpdump-3.7.1/libpcap-0.7.1).
> The interface in question, eth1, is a Linksys WMP11 wireless PCI card, using
> the orinoco_pci driver.
> The default route is to a Cisco 340 wireless access point.
>
> I have two problems:
> (1) While tracing using tcpdump or ethereal (regardless of whether in
> promiscuous mode or not), pings through the router fail with ICMP
> "Destination Host Unreachable" (apperently from the local host, not the
> router)
> (2) After the trace is finished, if the trace did *not* use promiscuous mode,
> pings through the router still fail.
>
> To get the interface out of the bad state of (2), I do either of the
> following:
> ifconfig eth1 promisc; ifconfig eth1 -promisc
> or:
> tcpdump -n -i eth1 (and then end it, with ^C)
> (note that starting and ending "tcpdump -p -n -i eth1" does *not* fix it).
>
> Running the debugger on tcpdump, I found out that the call in libpcap which
> causes the pings through the router to stop working is:
> setsockopt(sock_fd, SOL_PACKET, PACKET_ADD_MEMBERSHIP, &{ mr_ifindex =
> device_id, mr_type = promisc ? PACKET_MR_PROMISC : PACKET_MR_ALLMULTI })
My followup comment was
> To quote the comment in "__orinoco_set_multicast_list()" in the 0.13c version
> of the Orinoco driver at
>
> http://ozlabs.org/people/dgibson/dldwd/
>
> "The Hermes doesn't seem to have an allmulti mode, so we go into promiscuous
> mode and let the upper levels deal."
>
> Bleah.
>
> I'm inclined to just yank out the PACKET_MR_ALLMULTI, given that, as far as I
> know, doing non-promiscuous captures on a networking device doesn't muck with
> the set of multicast packets it receives.
So maybe it *does* muck with that set.
The section of code in question in the 0.13c driver is
/* The Hermes doesn't seem to have an allmulti mode, so we go
* into promiscuous mode and let the upper levels deal. */
if ( (dev->flags & IFF_PROMISC) || (dev->flags & IFF_ALLMULTI) ||
(dev->mc_count > MAX_MULTICAST(priv)) ) {
promisc = 1;
mc_count = 0;
} else {
promisc = 0;
mc_count = dev->mc_count;
}
if (promisc != priv->promiscuous) {
err = hermes_write_wordrec(hw, USER_BAP,
HERMES_RID_CNFPROMISCUOUSMODE,
promisc);
if (err) {
printk(KERN_ERR "%s: Error %d setting PROMISCUOUSMODE
to 1.\n",
dev->name, err);
} else
priv->promiscuous = promisc;
}
At one point while searching around on the Intertubes I thought I'd found a
version of the driver that actually treated allmulti differently by turning
some allmulti mode on, but I can't find it any more.
So perhaps the right thing to do here is to just say "if you have a wireless
adapter with the Hermes chipset and the firmware in question, you will get our
sympathy, but you won't get our support", and go back to turning
PACKET_MR_ALLMULTI on in non-promiscuous mode (and hope that either the
behavior Don Hatch found was the result of a bug somewhere in Linux that has
subsequently been fixed or that this is a quirk with some older network cards
and doesn't show up with newer network cards).
-
This is the tcpdump-workers list.
Visit https://cod.sandelman.ca/ to unsubscribe.
