Re: Command Preference?

Agreed... but that doesn't necessarily make it wrong. :)

Keep in mind that we're also working within the mindset that we've
always had these choices, which we have not. On routers (or some sets
of devices) you ONLY have the ignore option, or rework your MTUs. On
Catalyst switches specifically we have the extra, more elegant option of
setting the MTU for routing updates only to a certain value.

I don't view this as a CCIE tactic. It's not a convoluted solution that
was designed specifically for CCIE labs. It came about much earlier
than that, and some of the examples in Cisco docs have to do with FDDI
devices that defaulted to different MTU sizes depending on equipment.

Out of RFC compliance? Yeah, kinda. But that's there for a reason.
Kinda like speed limits. Your car still works fine above the speed
limit, right? I know mine does! :)

In networks, whether real life or in the lab, it's best to know WHY we
are using the commands that we are and what will be accomplished by
them. That way we can always make the appropriate choices.

*Scott Morris*, CCIE/x4/ (R&S/ISP-Dial/Security/Service Provider) #4713,

CCDE #2009::D, JNCIE-M #153, JNCIE-ER #102, CISSP, et al.

CCSI #21903, JNCI-M, JNCI-ER

swm_at_emanon.com

Knowledge is power.

Power corrupts.

Study hard and be Eeeeviiiil......

On 3/29/11 2:37 PM, aundra browning wrote:
> Cisco and other vendors should implement protocols according to standards
> defined by the IETF & others. In this case, RFC 2328 (section A.3.3) defined
> Interface MTU as a field in the database description packet (along with
> authentication, option flags, etc.) which is used to establish adjacency.
>
> In this case IOS is doing it's job - Interface MTU is a field that must be
> checked per the RFC......ignoring it by default wouldn't be RFC compliant.
>
> Just a thought.......
>
>
>
> On Tue, Mar 29, 2011 at 6:57 AM, garry baker <baker.garry_at_gmail.com> wrote:
>
>> this seems to be one of those things that goes under why doesnt Cisco the
>> great doer of magic just make this the default, to ignore the mtu...
>>
>> --
>> Garry L. Baker
>>
>> "With sufficient thrust, pigs fly just fine..." - RFC 1925
>>
>>
>>
>> On Tue, Mar 29, 2011 at 1:22 PM, Narbik Kocharians <narbikk_at_gmail.com
>>> wrote:
>>> Tyson,
>>>
>>>
>>>
>>> I see your point, and I totally respect it. But to me, telling the code
>> to
>>> ignore a check which maybe should not have been there to begin with is
>> more
>>> of a fix than a patch. But i could be wrong, i guess it all depends how
>> you
>>> look at it. But I definitely see what you are saying.
>>>
>>>
>>> On Tue, Mar 29, 2011 at 2:53 AM, Carlos G Mendioroz <tron_at_huapi.ba.ar
>>>> wrote:
>>>> +1
>>>>
>>>> ...although I would have said "instead of applying a patch to a
>> problem"
>>> :)
>>>> OSPF does this on purpouse, to test link is viable to carry small
>>> (hellos)
>>>> and large packets. Disabling the test is like silencing the alarm,
>>> problem
>>>> is still there, might byte you later.
>>>>
>>>> -Carlos
>>>>
>>>> Tyson Scott @ 29/03/2011 03:05 -0300 dixit:
>>>>
>>>> system mtu routing fixes a problem instead of applying a fix to a
>>> problem.
>>>>> Obviously you will always have to follow the lab requirements but my
>>>>> preference is simply a mindset. Just like with a real network.
>>>>> Preferably
>>>>> you will fix the underlying issues by fixing the design instead of
>>>>> applying "
>>>>> CCIE" tactics to work around issues.
>>>>>
>>>>>
>>>>>
>>>>> Regards,
>>>>>
>>>>>
>>>>>
>>>>> Tyson Scott - CCIE #13513 R&S, Security, and SP
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> From: Larry Hadrava [mailto:larryh12203_at_gmail.com]
>>>>> Sent: Monday, March 28, 2011 5:24 PM
>>>>> To: Narbik Kocharians
>>>>> Cc: Tyson Scott; Cisco certification; ALL From_NJ
>>>>> Subject: Re: Command Preference?
>>>>>
>>>>>
>>>>>
>>>>> Ok, I have to ask, Tyson, why do you prefer the system mtu routing
>> 1500
>>>>> choice?
>>>>>
>>>>> I would recommend to be careful with the wording of the requirement if
>>>>> this
>>>>> was in a lab setting to be sure which one they were asking you to use.
>>>>>
>>>>> The requirement might say - Do not disable mismatch detection on
>>>>> receiving
>>>>> DBD packets which would lead one to use the system mtu routing choice.
>>>>>
>>>>> If the requirement said - do not use any global configuration command
>> to
>>>>> allow
>>>>> the OSPF relationship to form, then that would lead to using the ip
>> ospf
>>>>> mtu-ignore command.
>>>>>
>>>>> Thanks
>>>>> Larry Hadrava
>>>>> CCIE #12203
>>>>> Check Out MyBlog: http://ccie12203.wordpress.com/
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> ----- Original Message -----
>>>>> From: "Narbik Kocharians" <narbikk_at_gmail.com>
>>>>> To: "ALL From_NJ" <all.from.nj_at_gmail.com>
>>>>> Cc: "Tyson Scott" <tscott_at_ipexpert.com>, "Cisco certification"
>>>>> <ccielab_at_groupstudy.com>
>>>>> Sent: Monday, March 28, 2011 5:10:10 PM GMT -05:00 US/Canada Eastern
>>>>> Subject: Re: Command Preference?
>>>>>
>>>>> The only reason i liked the "ip ospf mtu-ignore" is just incase i have
>>> to
>>>>> establish an OSPF session with another box. If this is configured,
>> then,
>>> i
>>>>> don't have to worry about it. But i am sure we all have our reasons
>> why
>>> we
>>>>> chose one option versus the other.
>>>>>
>>>>> On Mon, Mar 28, 2011 at 12:23 PM, ALL From_NJ <all.from.nj_at_gmail.com>
>>>>> wrote:
>>>>>
>>>>> Thanks everyone! I appreciate hearing your perspectives!
>>>>>>
>>>>>> .
>>>>>>
>>>>>> On Mon, Mar 28, 2011 at 2:40 PM, Tyson Scott <tscott_at_ipexpert.com>
>>>>>> wrote:
>>>>>>
>>>>>> I prefer the first.
>>>>>>> Regards,
>>>>>>>
>>>>>>> Tyson Scott - CCIE #13513 R&S, Security, and SP
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> -----Original Message-----
>>>>>>> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On
>> Behalf
>>> Of
>>>>>>> ALL
>>>>>>> From_NJ
>>>>>>> Sent: Sunday, March 27, 2011 9:01 PM
>>>>>>> To: Cisco certification
>>>>>>> Subject: Re: Command Preference?
>>>>>>>
>>>>>>> ok, sent too soon ... sorry about that.
>>>>>>>
>>>>>>> If you are allow to use either, do you have a preference when
>> peering
>>>>>> with
>>>>>>
>>>>>>> a
>>>>>>> switch?
>>>>>>>
>>>>>>> system mtu routing 1500
>>>>>>> or
>>>>>>> ip ospf ignore-mtu
>>>>>>>
>>>>>>> seems that setting the system mtu routing might save you some
>> trouble
>>>>>> later
>>>>>>
>>>>>>> on ...
>>>>>>>
>>>>>>> Your thoughts?
>>>>>>>
>>>>>>> Andrew
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> I know either one will work IF YOU ARE ALLOWED
>>>>>>>> --
>>>>>>>> Andrew Lee Lissitz
>>>>>>>> all.from.nj_at_gmail.com
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> Andrew Lee Lissitz
>>>>>>> all.from.nj_at_gmail.com
>>>>>>>
>>>>>>>
>>>>>>> Blogs and organic groups at http://www.ccie.net
>>>>>>>
>>>>>>>
>>> _______________________________________________________________________
>>>>>>> Subscription information may be found at:
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>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>> --
>>>>>> Andrew Lee Lissitz
>>>>>> all.from.nj_at_gmail.com
>>>>>>
>>>>>>
>>>>>> Blogs and organic groups at http://www.ccie.net
>>>>>>
>>>>>>
>> _______________________________________________________________________
>>>>>> Subscription information may be found at:
>>>>>> http://www.groupstudy.com/list/CCIELab.html
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>> --
>>>>> *Narbik Kocharians
>>>>> *CCSI#30832, CCIE# 12410 (R&S, SP, Security)
>>>>> www.MicronicsTraining.com <http://www.micronicstraining.com/> <
>>> http://www.micronicstraining.com/> <
>>>>> http://www.micronicstraining.com/>
>>>>> Sr. Technical Instructor
>>>>> *Ask about our FREE Lab Voucher with our Boot Camps*
>>>>> YES! We take Cisco Learning Credits!
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>>>>>
>>>>>
>>>>> Blogs and organic groups at http://www.ccie.net
>>>>>
>>>>>
>> _______________________________________________________________________
>>>>> Subscription information may be found at:
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>>>>>
>>>>>
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>>>>>
>>>>>
>> _______________________________________________________________________
>>>>> Subscription information may be found at:
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>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>> --
>>>> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina
>>>>
>>>
>>>
>>> --
>>> *Narbik Kocharians
>>> *CCSI#30832, CCIE# 12410 (R&S, SP, Security)
>>> www.MicronicsTraining.com <http://www.micronicstraining.com/> <
>>> http://www.micronicstraining.com/>
>>> Sr. Technical Instructor
>>> *Ask about our FREE Lab Voucher with our Boot Camps*
>>> YES! We take Cisco Learning Credits!
>>> Training & Remote Racks available
>>>
>>>
>>> Blogs and organic groups at http://www.ccie.net
>>>
>>> _______________________________________________________________________
>>> Subscription information may be found at:
>>> http://www.groupstudy.com/list/CCIELab.html
>>
>> Blogs and organic groups at http://www.ccie.net
>>
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>
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>
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Received on Wed Mar 30 2011 - 00:52:21 ART