RE: IP cef

After the MFI rewrite there is no Fast Path, you get either CEF or Process Switching. So 12.4(20)T and beyond are hard pressed to run without "ip cef" enabled.

--
http://dcp.dcptech.com
> -----Original Message-----
> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On
> Behalf Of Marko Milivojevic
> Sent: Friday, February 08, 2013 7:43 PM
> To: marc edwards
> Cc: Keller Giacomarro; Mohammad Mousa; Tauseef Khan; Cisco certification
> Subject: Re: IP cef
> 
> MPLS control plane does not require CEF. It's the MPLS forwarding
> plane that requires it. It makes up for an interesting troubleshooting
> :-).
> 
> Things change between IOS versions and behave differently on different
> platforms, but I recall that uRPF also needed CEF to work. I'm
> positive that ZBF needs it, as well (never tried it with CEF off
> though - feel free). On switches for example, you cannot turn CEF off
> if you have "ip routing" enabled, as it requires CEF to work.
> 
> --
> Marko Milivojevic - CCIE #18427 (SP R&S)
> Senior CCIE Instructor / Managing Partner - IPexpert
> 
> On Fri, Feb 8, 2013 at 4:36 PM, marc edwards <renorider_at_gmail.com> wrote:
> > Marko,
> >
> > Thanks for chiming in. I am interested to know what other control
> > protocols on blue print rely on CEF aside from MPLS?
> >
> > Marc
> >
> > On Fri, Feb 8, 2013 at 3:39 PM, Marko Milivojevic <markom_at_ipexpert.com>
> wrote:
> >> What if "ip routing" was disabled on routers? How about if escape
> >> character was set to "space", etc?  Paranoia, or "I'll always do this
> >> in a case they're playing games" will not get you very far in the lab
> >> :-).
> >>
> >> I recommend you do what's needed, no less, no more. If CEF is turned
> >> off, turn it on if you need it, otherwise, why do you care if it was
> >> turned off? :-)
> >>
> >> --
> >> Marko Milivojevic - CCIE #18427 (SP R&S)
> >> Senior CCIE Instructor / Managing Partner - IPexpert
> >>
> >> On Fri, Feb 8, 2013 at 1:30 PM, Keller Giacomarro <keller.g_at_gmail.com>
> wrote:
> >>> I have a pre-defined set of commands I run on all my configuration-
> section
> >>> devices before I start the section.
> >>>
> >>> ***
> >>> ip cef (doesn't work on switches without 'ip routing' enabled)
> >>> ip classless
> >>> ip subnet-zero
> >>> ***
> >>>
> >>> My logic is -- If any of these are disabled, it's most likely going to be a
> >>> purposeful 'break' that you have to fix.  If they want them to stay
> >>> disabled, they'll tell you in the questions.  Either way, it doesn't hurt
> >>> you to run all three by default on all devices.
> >>>
> >>> One that I DON'T run is 'ip routing'.  It's not a given that all switches
> >>> will be running routing protocols, and when you enable IP routing it
> >>> disables the default-gateway, which means adding a static route.  This is
> >>> probably not allowed in your lab.
> >>>
> >>> I have another tip for the troubleshooting section.  I put this text into
> >>> notepad and copy-paste it into every device I open as I open them.
> >>>
> >>> ***
> >>> conf t
> >>> logging con debug
> >>> end
> >>> copy running-config nvram:original.cfg
> >>>
> >>> n
> >>>
> >>>
> >>> ***
> >>>
> >>> First, this ensures I can see all logging outputs.  If it's the first time
> >>> I've accessed the device, the config is backed up to nvram:original.cfg,
> >>> and the 'n' will be an invalid command.  If it's NOT the first time I've
> >>> accessed the device, the newline and the n means original.cfg will NOT
> get
> >>> overwritten (answers 'no' to 'do you want to overwrite').  I save to
> nvram:
> >>> instead of flash: just in case their IOU instances do not have a flash --
> >>> all devices have nvram.
> >>>
> >>> A quick 'end' and then 'wr' before I close ANY window ensures that all
> my
> >>> work gets saved too.
> >>>
> >>> This works great for me, what is your strategy?
> >>>
> >>> Keller Giacomarro
> >>> keller.g_at_gmail.com
> >>>
> >>>
> >>> On Fri, Feb 8, 2013 at 11:34 AM, marc edwards <renorider_at_gmail.com>
> wrote:
> >>>
> >>>> I can think of at least one control protocol on the blueprint that
> >>>> won't work w/out CEF (MPLS). Can anyone else add to the list?
> >>>>
> >>>> Marc
> >>>>
> >>>> On Fri, Feb 8, 2013 at 8:03 AM, Mohammad Mousa <mohd-
> mousa_at_hotmail.com>
> >>>> wrote:
> >>>> > Tauseef,
> >>>> >
> >>>> > I think you've to enable them, because some of the services won't
> work
> >>>> well unless you enable IP CEF/IPV6 CEF, and I think you won't get the
> >>>> complete mark unless you put these commands.
> >>>> >
> >>>> > HTH,
> >>>> >
> >>>> > -Mohammad Mousa
> >>>> > CCIE #36990
> >>>> >
> >>>> >> Date: Fri, 8 Feb 2013 15:33:50 +0000
> >>>> >> Subject: IP cef
> >>>> >> From: tasneemjan_at_googlemail.com
> >>>> >> To: ccielab_at_groupstudy.com
> >>>> >>
> >>>> >> If in the lab ip cef is disabled on the routers and I enable ip cef /
> >>>> ipv6
> >>>> >> cef on routers, will I lose marks for that, as over configuration.
> >>>> Without
> >>>> >> ip cef every thing will be process switched but still all the routing
> >>>> will
> >>>> >> work as normal. Appreciate if someone could explain?
> >>>> >> Regards
> >>>> >>
> >>>> >>
> >>>> >> Blogs and organic groups at http://www.ccie.net
> >>>> >>
> >>>> >>
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