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
>>>> >>
>>>> >>
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>>>
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