Jarek Poplawski [off-list ref] writes:

On Wed, Nov 05, 2008 at 11:30:45AM +0100, Ferenc Wagner wrote:

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Jarek Poplawski [off-list ref] writes:

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On Sun, Nov 02, 2008 at 12:55:56AM +0100, Ferenc Wagner wrote:

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Jarek Poplawski [off-list ref] writes:

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On Wed, Oct 29, 2008 at 05:56:17PM +0100, Ferenc Wagner wrote:

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Jarek Poplawski [off-list ref] writes:

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Ferenc Wagner [off-list ref] writes:

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I expected an IP-less bridge interface to pick up no IP
packets, but apparently this isn't the case: broadcast packets
with destination address 255.255.255.255 are reported as
martians by the 2.6.18 kernel, which I find counterintuitive (I
know 2.6.18 is rather old, but that's the one supported by Xen).

  1. Is this the expected behaviour?

with IP disabled you shouldn't have any martians!

In my case, the bridge itself (?) has no IP addresses assigned, but
an other interface (which isn't a bridge port) does have.  In other
words, the only network interface of the host is a bond interface
aggregating the two physical Ethernet interfaces; the two IP
addresses of the host are assigned to this bond0.

bond0 is also the raw interface of several .1q VLAN interfaces,
which are ports of bridges (there is one bridge for each VLAN but
the native above).  The other ports of the bridges are the virtual
interfaces of the Xen guests running on this host.  If I run ping
-b 255.255.255.255 on one such guest, that gives a "martian source
255.255.255.255" warning on the given bridge.  Even though
255.255.255.255 is the destination address of that ping packet...

And this happens on 2.6.26.6, too.

This means that even with IP enabled device ip_mkroute_input() should
be skipped. So it seems it's not about 255.255.255.255 generally, but
just about source address. You didn't give any examples of these
warnings, but I guess it's not a 0 address which is most popular with
255.255.255.255.

Indeed not, sorry.  If I ping -b 255.255.255.255 on a virtual machine
with IP 193.225.14.155, whose virtual interface is a port of br891:

martian source 255.255.255.255 from 193.225.14.155, on dev br891

I hope it's not the autoconfigured IPv6 addresses...

I hope too... Anyway, I did some checking and this all seems to be a
real puzzle. As I wrote earlier (according to the comment): "with IP
disabled you shouldn't have any martians!". But it looks like deleting
all inet addresses isn't enough to have this "IP disabled" status
(maybe it's about multicasts or something... - I still have to find the
reason), but it's probably not critical for this problem.

Then I guess we can reconsider this problem like this: since this is a
bridge device without any IP address, and "we" expect treating this as
IP disabled devices, IMHO it doesn't make much sense to turn rp_filter
for such a device; log_martians can report us some other strange
address combinations, so it could be useful if there is not too much
of this.

Yes, rp_filter doesn't make any sense on this bridge interface, as
there should be no traffic to/from the bridging host through this
bridge.  Still, it shouldn't hurt either, should it?

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wferi@xen1:~$ sudo cat /proc/net/vlan/vlan891 
[...]
EGRESSS priority Mappings: 

Should be corrected: maybe you will send a patch? (Otherwise let me now.)

I sent one.  Hope it's OK.

Yes, but this 255.255.255.255 address is (or was) special. According
to this:
http://en.wikipedia.org/wiki/Classful_network
and especially this:
http://tools.ietf.org/html/draft-wilson-class-e-02

it could be changed soon.

Yes, but I fail to see how this is relevant in either case.  My
question is: why does the IP-less bridge pick up any packets?
Does the host-based addressing model require this, if the host has any
IP address at all (on some other interface)?

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And, if there is some network address we have a problem: AFAIK this
255.255.255.255 broadcast is special, and it shouldn't be routed to
other networks. Your host doesn't seem to recognize this network, so
it shouldn't happen on this interface. So it seems, you expect the
bridge behavior where it's 2 in 1 (bridge + IP host).

Yes, this machine is an IP host (SSH access is needed) in a private
subnet (10.253.2/24) and also bridges traffic belonging to other
subnets (like for example the above).  It is not a router, though, so
it knows nothing about the bridged subnets.  Actually, it should be
totally separated from those, that's why I was alarmed by the martian
warnings: these "limited broadcast" (255.255.255.255, not routed, as
you note) addressed packets could reach the bridge!

Wasn't this ping done within the bridge's reach?

I'm not sure what you mean.  It was done on a virtual machine, whose
virtual inteface (vif4.0) is a port of br891 (see above).

I'm not sure what you mean by "totally separated". Bridges usually
don't help to separate, and packets with proper or not proper (for some
network) addresses are forwarded.

I didn't mean separating the ports of the bridge, but separating the
host running the bridge from the traffic the bridge forwards.  It
should be able to forward all the strangest IP or non-IP traffic of
the world and stay totally unaffected.

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but not all. log_martians should tell you if it's something
serious. If you have some martians "by design" it's probably
better to get rid of them before rp_filter

By dropping the in the nat table or by ebtables?  Anyway, "martians by
design" does sound particulary sane.

I mean e.g. when you really have to treat packets with such unusual
addresses as in your pings.

Yes, I have to.  Some Wake-on-LAN packets also carry 255.255.255.255
as their destination address.  Just like various Windows/MacOS
"neighbour discovery" services.

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I agree the syntax of this warning is confusing, but I doubt we
should change this after so many years - this could break users'
scripts checking for this.

:) It's surprising after having read stable_api_nonsense.txt...

Hmm... Could you point me to this most :) point?

For me, the first paragraph says that the user space interface is the
syscall interface, and that's the only one you can count on being
stable; in other cases technical superiority overrides compatibility.
Not that I feel too strongly in this case.
-- 
Regards,
Feri.