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Re: [libvirt] [libvirt PATCHv4 0/2] DHCP Snooping support for libvirt



On 10/25/2011 02:01 PM, David Stevens wrote:
Stefan,
         Thanks for reviewing.

Stefan Berger<stefanb linux vnet ibm com>  wrote on 10/25/2011 04:59:16
AM:

I hope that this code will be able to support multiple IP addresses once
my patches have gone in.
         I labelled in the code with comments the places that need to be
revised (3, I believe) for multiple address support.  I added one check to
ignore
an additional address when you already have one for an interface. The
other
depends on the form of multiple address support. If it is a mechanism
that changes variable values (either add or remove) in place in the
filters,
it'll be reverting to code similar to my first post. If it uses something
like virNWFilterInstantiateFilterLate(), my main concern is making sure
there isn't a window while deleting or adding an address that rebuilds the
entire filter where either no packets or spoofed packets would be allowed.
This should not be possible to happen during this call. The new filter is built while the old filter is still active. The new filter is connected to the 'root' where all filters are connected to and only then the old one is disconnected and deleted. So the switch-over is 'atomic'. Though this *may* need re-visiting in case *all* leases expiring and IP = <empty> and one has to put in the DHCP-only filter now.
Both cases would need to remove the DHCP-only rule installation in delete,
since removing one of multiple addresses shouldn't remove the other
address(es)'s
filters.
         The internal snooping code supports multiple addresses per
interface as
before. It assumes 1-interface==1-network as before, so your comments
about
VLANs and the leasefile also require a visit, but don't apply without
multiple
address support in the rest of nwfilter. Tracking and saving the VLAN ID
or saving and matching the DHCP client ID should do that.

We'll get to that.

   Stefan
  +-DLS



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