Re: OER External interface Null0

That's a good point. You don't HAVE to do it, but you'd still need to have
two interfaces to make PfR work at all. So, if you wanted that
functionality, it only stands to reason that Null0 would be defined as a
dummy 2nd external interface.

I think we reasoned it through, don't you think? :-)

--
Marko Milivojevic - CCIE #18427 (SP R&S)
Senior CCIE Instructor - IPexpert
On Mon, Mar 26, 2012 at 20:08, Tom Kacprzynski <tom.kac_at_gmail.com> wrote:
> Marko,
> Thank you for your response.
>
> I did find one reference of the null interface as a next hop with an
> OER-map
> http://www.cisco.com/en/US/docs/ios-xml/ios/oer/configuration/12-4t/oer-cfg-apply.html#GUID-5592C6F1-2C89-4197-A6DD-ABF807025579
> but for this feature to work I don't think you have to setup Null0 to be an
> *external interface*. Basically they are saying this is a black hole
> policy for a specified prefix traffic-class.
>
> Config from the link:
>
> enable
> configure terminal
> ip prefix-list PREFIX_BLACK_HOLE seq 10 permit 10.1.5.0/24
> oer-map <http://10.1.5.0/24oer-map> BLACK_HOLE_MAP 10
>  match ip address prefix-list PREFIX_BLACK_HOLE
>  set interface null0
>  end
>
> Regards,
>
> Tom
>
>
>
> On Mon, Mar 26, 2012 at 9:46 PM, Marko Milivojevic <markom_at_ipexpert.com>wrote:
>
>>
>> That's a good question. If you have only one external interface, what's
>> the point of PfR to begin with? So, I'm thinking that the reasons are not
>> just making 2nd interface appear, even though I might be wrong. I'm more
>> thinking of a possibility to use that as an exit interface to drop certain
>> traffic if a condition is met. I'd struggle coming up with a scenario to
>> use it in real life though.
>>
>> --
>> Marko Milivojevic - CCIE #18427 (SP R&S)
>> Senior CCIE Instructor - IPexpert
>>
>> On Mon, Mar 26, 2012 at 18:27, Tom Kacprzynski <tom.kac_at_gmail.com> wrote:
>>
>>> Hello,
>>> I noticed that you can specify a Null0 interface as an external interface
>>> in OER. Does anyone know where you would use that?
>>>
>>> The only thing I could see that being used for is if you have to shutdown
>>> one of the border routers and your total number of external interfaces
>>> drops below 2 (which causes the master controller to become inactive). By
>>> configuring a null0 interface as an external interface, the master
>>> controlled comes up as active.
>>>
>>> Are there any other instance where that would make sense to configure a
>>> null0 as an external interface?
>>>
>>> r3(config-oer-mc-br)#interface null0 external
>>>
>>>
>>> Thanks
>>>
>>> Tom
>>>
>>>
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