[Snort-users] IDS Placement ideas for inside and outside a firewall.

David Glosser david_glosser at ...131...
Thu Apr 3 22:12:40 EST 2003


MessageWhat if a host was compromised and your snort didn't pick it up (say b/c snort was down, a ras server was used, or a malicious end-user). Then that server probes and compromises other servers...  The sensor would never pick it up, since it is only monitoring the firewall....

----- Original Message ----- 
  From: Ponte, Paul F 
  To: 'snort-users at lists.sourceforge.net' 
  Sent: Thursday, April 03, 2003 10:03 PM
  Subject: RE: [Snort-users] IDS Placement ideas for inside and outside a firewall.


  Hi all -
    I'd like to ask your opinions on one part of this question.  When we talk about a sensor on the inside of the firewall, I assume that means it can see all traffic on the internal subnet.  But what do you give up if you monitor just traffic passing on a VLAN between the firewall and the router sitting between it and the rest of the network?  Is this a valid installation?  What's the danger in not monitoring all of the normal host to host traffic on your network which doesn't need to cross the firewall?  I'm considering this kind of deployment, so thanks for your opinions on this.

  Paul
    -----Original Message-----
    From: Brian Laing [mailto:Brian.Laing at ...8609...] 
    Sent: Thursday, April 03, 2003 5:58 PM
    To: 'Brei, Matt'; 'David Glosser'; 'FWAdmin'; snort-users at ...4137...orge.net
    Subject: RE: [Snort-users] IDS Placement ideas for inside and outside a firewall.


    It can help, but I would not rely on it for prosecution the fact is the data is too easy to spoof and is not collected in a forensically sound manager either at the sensor or the management console.  By forensically sound I mean certified to be free from tampering.  Not that this data wont help your case, but its better to rely on it to see where and into what else the attacker may have gotten into.

     

    -------------------------------------------------------------------
    Brian Laing
    CTO
    Blade Software
    Cellphone: +1 650.280.2389
    Telephone: +1 650 367.9376
    eFax: +1 208.575.1374
    Blade Software - Because Real Attacks Hurt
    http://www.Blade-Software.com
    -------------------------------------------------------------------

    -----Original Message-----
    From: Brei, Matt [mailto:mbrei at ...8727...] 
    Sent: Thursday, April 03, 2003 2:18 PM
    To: brian.laing at ...8607...; David Glosser; FWAdmin; snort-users at ...1844...ourceforge.net
    Subject: RE: [Snort-users] IDS Placement ideas for inside and outside a firewall.

     

    That's exactly why I would want one outside of the firewall.  If I were to find a successful break in, I could then review logs from the external IDS and find that the same IP had done several scans or whatever that were eventually blocked by the firewall and not picked up by the internal IDS.  I would think that this would help build a better case if any type of legal action were to be taken. 

     

    Matt

     

    -----Original Message-----
    From: Brian Laing [mailto:Brian.Laing at ...8609...] 
    Sent: Thursday, April 03, 2003 11:28 AM
    To: 'David Glosser'; Brei, Matt; 'FWAdmin'; snort-users at ...3471...ge.net
    Subject: RE: [Snort-users] IDS Placement ideas for inside and outside a firewall.

     

    I would agree with this sort of implementation, in many of the installs I have done I will setup the external sensors to do nothing but logging and ignore the data till I see something worth looking at on one of the internal servers.  I use this data to see what else that IP has been doing or what other things have been attempted against a specific host

     

    -------------------------------------------------------------------
    Brian Laing
    CTO
    Blade Software
    Cellphone: +1 650.280.2389
    Telephone: +1 650 367.9376
    eFax: +1 208.575.1374
    Blade Software - Because Real Attacks Hurt
    http://www.Blade-Software.com
    -------------------------------------------------------------------

    -----Original Message-----
    From: snort-users-admin at lists.sourceforge.net [mailto:snort-users-admin at lists.sourceforge.net] On Behalf Of David Glosser
    Sent: Wednesday, April 02, 2003 11:10 PM
    To: Brei, Matt; FWAdmin; snort-users at lists.sourceforge.net
    Subject: Re: [Snort-users] IDS Placement ideas for inside and outside a firewall.

     

    If you've never set up any IDS before, I'm not sure you would want to place it outside your firewall immediately You'lll get overwhelmed with probes,scans, script kiddies etc. 

    First place the box (with the "snorting" NIC unnumbered). On the port monitoring the *internal* interface of your firewall. Let it work on all of the stuff your firewall lets through. Once you have that under control, then place another box (or another NIC on the same box) to monitor your internal servers (since breakins can come from internal users). 

    Once you have these two under control, then you can worry monitoring stuff outside the firewall,  which I believe is called *attack detection*. But do you care that much about the stuff your firewall is successfully blocking?

     

    --snip-

       I am trying to convince my company to implement IDS on our network but I have a few questions. I know I would want one on both sides of the firewall, 




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