Re: IPS/IDS behavior with ISIC/UDPSIC/TCPSIC/ICMPSIC traffic

["Ravi Chunduru" <ravi.is.chunduru () gmail com>]

tcpsic program today is not completing three way handshake.  What
about tools and attacks that complete three way handshake?  recently
cnn.com was DDOSed by  set of people in china during tibet unrest
time.  This attack was not only completing three way handshake, but
also downloading content from a specific URL.   My questions.

Why is this not considered in NSS testing criteria? Is it not
considered as an attack that need to be protected by IPS devices?

Ravi

On Wed, May 7, 2008 at 5:41 PM, Srinivasa Addepalli <srao () intoto com> wrote:
> ISIC generates many packets with different IP protocols.  If you have
> firewall, you can block the protocols which you don't require. Also, it
> generates UDP, TCP packets with wrong checksum. Since IPS software drops the
> packets with wrong checksum, this may not be the cause for either 100% CPU
> utilization or running out of session entries.
>
> TCPSIC: Since many IPS boxes have SYN flood protection, this also may not be
> the reason for the problem you are facing.
>
> UDPSIC: This can use up all resources. If you have connection rate limit
> function, then utilize it to limit the rate. Typically, each session is kept
> for inactivity timeout period. If number of new packets within this timeout
> period exceed number of session entries the IPS box supports, then further
> new connections are not entertained. If the connection rate limit is set to
> less than <Number of session entries supported by IPS>/<inactivity timeout>,
> then IPS session entries don't get exhausted.
>
> If you still see 100% CPU problem, you may like to check you log settings.
> If connection logging (for NBA) is enabled, then for every packet it might
> be generating a log message and that might exhaust CPU.
>
> Even though it is obvious, let me state it anyway :-). If the input packet
> rate is more than the CPU (that is running IPS) can process, then you see
> 100% CPU problem.
>
> Thanks
> Srini
>
>
> -----Original Message-----
> From: listbounce () securityfocus com [mailto:listbounce () securityfocus com] On
> Behalf Of Ravi Chunduru
> Sent: Wednesday, April 30, 2008 8:22 AM
> To: focus-ids () securityfocus com
> Subject: IPS/IDS behavior with ISIC/UDPSIC/TCPSIC/ICMPSIC traffic
>
> According to NSS testing criteria,  the IPS/IDS devices are expected
> to work normally even during the time *SIC traffic is sent at
> 60000pkts/sec with each packet size of 690 bytes. I find that inline
> snort IPS software based PC device stops passing any legitimate
> traffic when this *SIC traffic is sent at very high speed.  As such I
> also see this problem even if UDPSIC traffic (with random ports) is
> passed with 50000 pkts/sec.   Once the traffic is stopped, it starts
> working normally. Note that if I use UDPSIC with fixed port, then I
> don't see the problem of 100% CPU utilization and other traffic passes
> normally.
>
> I am using PC with P4 processor running at 2.8Ghz.
>
>
> Is there any significance to 60000 pkts/sec NSS number? Also, what is
> the expected behavior of IPS software during this load?
> Does NSS test with random UDP ports? Or do they use one fixed port
> while running UDPSIC and TCPSIC?
>
> Thanks
> Ravi
>
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