[Snort-users] Snort inline latency

Ian Bowers iggdawg at ...11827...
Fri May 4 16:18:54 EDT 2012


If you have a VLAN capable switch, use VLANs to place the snort sensor
inline.  run your tests, calculate latency.  Then use VLANs to take the
sensor out of line.  repeat tests.  Do this a couple times to make sure you
have consistent results.   I use this technique all the time in my lab to
toss test appliances or VMs in the path of traffic without having to mess
around with cables like.  IE:

Snort inline:
Server --- VLAN 102 ---- snort --- VLAN 103 --- router --- client

Snort removed:
Server --- VLAN 102 --- router --- client
   VLAN 104 --- snort --- VLAN 104

inline, both sides of snort are on different VLANs, and act as if they're
on their own little switches.  The switchports are access ports so the end
devices don't see the VLAN tags.  In the second scenario, snort sits in its
own little penalty box on VLAN 104 where the two sensor ports don't talk to
anyone.  the router and the server are both on VLAN 102 at this point and
can communicate directly.  I'm assuming a router is involved but it doesn't
have to be.   just eliminate the router and put the client in its place,
works the same.  I pick random VLANs in the 100s for most examples to
discourage people from using native VLANs by mistake since that may break
the scanario.


Example switch config if you're using Cisco gear:

INLINE:
vlan 102
 name servernet_inside
vlan 103
 name servernet_outside

interface FastEthernet0/4
 description Server access port
 switchport access vlan 102
 switchport mode access
!
interface FastEthernet0/5
 description Snort HOME_NET port
 switchport access vlan 102
 switchport mode access
!
interface FastEthernet0/6
 description Snort EXTERNAL_NET port
 switchport access vlan 103
 switchport mode access
!
interface FastEthernet0/7
 description Router access port
 switchport access vlan 103
 switchport mode access


REMOVED:

vlan 102
 name servernet_inside
vlan 104
 name on_deck

interface FastEthernet0/4
 description Server access port
 switchport access vlan 102
 switchport mode access
!
interface FastEthernet0/5
 description Snort HOME_NET port
 switchport access vlan 104
 switchport mode access
!
interface FastEthernet0/6
 description Snort EXTERNAL_NET port
 switchport access vlan 104
 switchport mode access
!
interface FastEthernet0/7
 description Router access port
 switchport access vlan 102
 switchport mode access


Regards,
-Ian


On Fri, May 4, 2012 at 3:35 PM, Abdelmonaim Mokadem <
abdelmonaim.mokadem at ...13827...> wrote:

>  Hi all,****
>
> I am currently trying to calculate my snort inline latency.****
>
> I have 2 hosts : one running snort inline and the other one which inject
> pcaps (a bridge is set to send back packets from the snort host machine to
> the injection one).****
>
> I use tcpdump to sniff packets at the emission and at the reception from
> my injection host and (I match only ACK packets with a little program) then
> calculate the difference between the timestamps (emission and reception),
> but unfortunately my results are really bad…****
>
> Can anyone tell me if I’m doing right? Or does anyone know what is the
> best way to calculate snort inline latency?****
>
> Thanks,****
>
> AM.****
>
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