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xen-users
Re: [Xen-users] Snort monitoring of Xen guests
 
John Haxby wrote:
 
Mark Chandler wrote:
 
Hi all,
 From another post on this list, it seems that the only way to monitor 
all traffic to guests in a host is to bind to the peth interface that 
is bound to the bridge that serves the guests. Is this the only way 
of doing it? Ideally, I'd like to have one guest running Snort that 
monitors everything else.
 
ebtables is probably your friend.   Something like
   ebtables -t broute -A BROUTING -s <dom0 MAC> -j ACCEPT
   ebtables -t broute -A BROUTING -d <dom0 MAC> -j ACCEPT
   ebtables -t broute -A BROUTING -s <domU MAC> -j ACCEPT
   ebtables -t broute -A BROUTING -d <domU MAC> -j ACCEPT
    ebtables -t broute -A BROUTING -p IPv4 --ip-proto tcp -j dnat 
--to-dst <domU MAC> --dnat-target ACCEPT
 Where <domU MAC> is the MAC address of the guest you want to run snort 
on.  The first four rules ensure that traffic from dom0 and the 
monitoring domU pass unimpeded through the bridge, the last rule 
redirects all traffic TCP traffic to or from any other guest through 
the monitoring domU.
 Of course, it doesn't have to be a domU on this machine, it can be any 
machine, virtual or otherwise, on the LAN since you're just 
redirecting traffic at the layer 2 level.  You'll probably want to do 
more with the last rule as well, as you'll probably want some (or all) 
UDP traffic redirected to the monitor but you might want to draw the 
line at ICMP, ARP and Appletalk :-)
jch
  Many thanks, John. I'll give that a go. At the very least it'll be fun 
to experiment with ebtables! :-)
Mark C.
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