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Re: [Xen-devel] [RFC v2 2/4] net: enables interface option to skip IP

On Tue, Feb 25, 2014 at 04:18:17PM -0500, David Miller wrote:
> From: Dan Williams <dcbw@xxxxxxxxxx>
> Date: Tue, 25 Feb 2014 15:07:00 -0600
> > Also, disable_ipv4 signals *intent*, which is distinct from current
> > state.
> > 
> > Does an interface without an IPv4 address mean that the user wished it
> > not to have one?
> > 
> > Or does it mean that DHCP hasn't started yet (but is supposed to), or
> > failed, or something hasn't gotten around to assigning an address yet?
> > 
> > disable_ipv4 lets you distinguish between these two cases, the same way
> > disable_ipv6 does.
> Intent only matters on the kernel side if the kernel automatically
> assigns addresses to interfaces which have been brought up like ipv6
> does.
> Since it does not do this for ipv4, this can be handled entirely in
> userspace.
> It is not a valid argument to say that a rogue dhcp might run on
> the machine and configure an ipv4 address.  That's the admin's
> responsibility, and still a user side problem.  A "rogue" program
> could just as equally turn the theoretical disable_ipv4 off too.

Week end model strikes again. :)

Currently one would need to set arp_filter and arp_ignore and have no
ip address on the interface to isolate it from the ipv4 network.

IFF_NOARP is of no use here as it also disables neighbour discovery.

I am not sure we completley tear down igmp processing on that interface
if no ip address is available. Maybe there are some special cases with
forwarding, too.

Such a "silent" mode could come handy for intrusion detection systems
where one would ensure that no ip processing takes place but could also
be realized with nftables/netfilter/arpfilter, I think.



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