From: Nadeem Ansari (nadeem.ansari574@gmail.com)
Date: Sun Feb 22 2009 - 11:56:57 ARST
Thanx Scott for your good explanation , Cisco routers are always vulnerable
to high CPU utilization whenever we enable some features other than routing
& forwarding :)
Regards
Nadeem
On Sat, Feb 21, 2009 at 11:52 PM, Scott M Vermillion <
scott_ccie_list@it-ag.com> wrote:
> I don't think Cisco has ever released too much in the way of
> "under-the-hood" details of the actual mechanics of NBAR. However, in
> Chapter 3 of "End-to-end QoS Network Design," there's a short one-paragraph
> discussion that delves into NBAR and CEF. It says:
>
> "NBAR is dependent on Cisco Express Forwarding (CEF) and performs
> deep-packet classification only on the first packet of a stream. The
> remainder of the packets belonging to the stream are then CEF-switched."
>
> I have also seen Cisco/Cisco Press literature where NBAR is described as
> highly CPU-intensive (not surprisingly). So perhaps the CEF requirement
> just has more to do with self-preservation than the actual mechanics of how
> it actually works; doing NBAR _and_ process switching might very well
> result
> in some bad behavior on the part of a router, so they simply don't allow
> it.
> Sounds good on paper anyway...
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> dave
> dave
> Sent: Thursday, February 19, 2009 10:58 PM
> To: Cisco certification
> Subject: IP CEF required for NBAR what logic?
>
> Hi Expert,
>
> Why do we need to enable "ip cef" when using the "NBAR protocol", no
> explanation found on this. I have enable "ip cef" then configure "NBAR"
> then
> i removed "no ip cef" & "NBAR" was working fine :((( not understand the
> logic behind this.
>
> r1(config-if)#ip nbar protocol-discovery
> CEF or distributed CEF switching is required for NBAR 'protocol discovery'
> command
>
> Regards
> Dave
>
>
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