From: CCIE To Be (ccie.tobe81@gmail.com)
Date: Tue Jan 13 2009 - 16:45:16 ARST
Nice explainations !!!
Here is a question that R1 is advertising a prefix and requirement
says, configure R1 so that this prefix should not be advertised outside AS
10. Now we have 2 options here,
1) set no-export community on R1 towards R2.
2) set local-as community on R1 towards R2.
What should be the deciding factor to prefer 1 method over other ??
HTH
On Tue, Jan 13, 2009 at 5:59 PM, Pavel Bykov <slidersv@gmail.com> wrote:
> It's extremely important where you set the attribute in this example and
> direction of the update. If the update travels R1>R2>R3, then:
>
> 1. NO-ADVERTISE:
> - If you set it on R1 directly (like network x.x.x.x route-map XYZ), R2
> will not receive route.
> - If you set it on R1 as route-map to R2, R2 will receive and use route,
> but will not advertise it to R3
> - If you set it on R2, R3 will use route, but will not advertise it to any
> other neighbor.
>
> 2. NO-EXPORT:
> If you set it on R1, R2 will receive and use route, but will not advertise
> it to R3 (route will stay in AS 10)
> If you set it on R2, R3 will receive and use route, but route will not get
> out of AS 30
>
> 3. LOCAL-AS:
> Same as no-export, but also valid for BGP confederations.
>
>
> On Mon, Jan 12, 2009 at 10:57 PM, Jason Morris <mcnever@gmail.com> wrote:
>
>> for local-as to work you would have to set that community inbound on
>> R3. If that's out of your domain that's not really an option. If you
>> set the local-as community while its still inside AS10 it wont get
>> advertised out.
>>
>> no-export = AS10 telling AS30 not to tell anyone else
>>
>> local-as = AS10 not telling AS30 at all
>>
>> or at least that's my understanding
>>
>>
>>
>>
>> On Mon, Jan 12, 2009 at 3:27 PM, CCIE To Be <ccie.tobe81@gmail.com>
>> wrote:
>> > Got it....
>> >
>> > Other question is related to local-as community. Let suppose we don't
>> want
>> > to advertise a specific prefix outside 'AS 10' then we will have again
>> same
>> > option of no-export. What about using local-as community in this
>> scenario
>> > which will not allow a particular prefix to go out of local AS 10 ??
>> >
>> >
>> >
>> > On Tue, Jan 13, 2009 at 12:01 AM, Huan Pham <pnhuan@yahoo.com> wrote:
>> >
>> >> No-export of course!
>> >>
>> >> Using no-advertise will prevent prefixes received from AS10 to be
>> >> advertized to R3 iBGP peers as well which are undesirable here.
>> >>
>> >> Sent from my iPhone
>> >>
>> >> On 13/01/2009, at 6:28 AM, CCIE To Be <ccie.tobe81@gmail.com> wrote:
>> >>
>> >> Dear Group,
>> >>
>> >> I have a confusion regarding usage of no-advertise and no-export
>> >> communities. I know that no-advertise means NOT TO ADVERTISE to any bgp
>> >> peer
>> >> ( iBGP & eBGP ) whereas no-export says NOT TO ADVERTISE to any eBGP
>> peer
>> >> means don't advertise outside this AS. Consider the following topology,
>> >>
>> >> R1(AS 10) --------R2(AS 10)------------R3(AS 30)
>> >>
>> >> Let say AS 10 is advertising a prefix to AS 30 and requirement is that
>> AS
>> >> 30
>> >> should not forward this prefix further to any other AS. Now we have
>> option
>> >> to use either no-advertise or no-export on R2 towards R3. Both will
>> give
>> >> the
>> >> desired result , what should be the recommended approach here ??
>> >>
>> >>
>> >> HTH
>> >>
>> >>
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>>
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>>
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>>
>>
>>
>>
>>
>>
>>
>
>
> --
> Pavel Bykov
> ----------------
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