[libvirt] [PATCH[ nwfilter: Discard class D and E IP addresses when sniffing

[Stefan Berger]

libvir-list-bounces at redhat.com wrote on 08/13/2010 03:11:25 PM:


> 
> On 08/13/2010 12:38 PM, Stefan Berger wrote:
> >  When sniffing the network traffic, discard class D and E IP addresses
> > when sniffing traffic. This was a reason why filters were not 
correctly
> > rebuilt on VMs on the local 192.* network when libvirt was restarted 
and
> > those VMs did not use a DHCP request to get its IP address.
> > 
> > Signed-off-by: Stefan Berger <stefanb at us.ibm.com>
> > 
> > ---
> >  src/nwfilter/nwfilter_learnipaddr.c |    7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > Index: libvirt-acl/src/nwfilter/nwfilter_learnipaddr.c
> > ===================================================================
> > --- libvirt-acl.orig/src/nwfilter/nwfilter_learnipaddr.c
> > +++ libvirt-acl/src/nwfilter/nwfilter_learnipaddr.c
> > @@ -546,9 +546,12 @@ learnIPAddressThread(void *arg)
> >                      struct iphdr *iphdr = (struct iphdr*)(packet +
> > ethHdrSize);
> >                      vmaddr = iphdr->saddr;
> > -                    // skip eth. bcast and mcast addresses,
> > +                    // skip eth. bcast and mcast addresses (224.0.0.0 
-
> > +                    // 239.255.255.255), class E (255.*)
> >                      // and zero address in DHCP Requests
> > -                    if ((ntohl(vmaddr) & 0xc0000000) || vmaddr == 0) 
{
> > +                    if ( (ntohl(vmaddr) & 0xe0000000) == 0xe0000000 
||
> 
> This line's fine for 224-239.*, but...
> 
> > +                         (ntohl(vmaddr) & 0xf0000000) == 0xf0000000 
||
> 
> shouldn't this be (ntohl(vmaddr) & 0xff000000) == 0xff000000, so that
> you are not excluding 254.*?
> 

Looking at Wikipedia for this

http://en.wikipedia.org/wiki/Classful_network

Class D addresses have highest bits with pattern 1110 0000 -> 0xe0
Class E addresses have highest bits with pattern 1111 0000 -> 0xf0

I think my masks are fine and the masking with 0xf0 00 00 00 should also 
include 254.*  =  0xfe.*  .

   Stefan
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