Re: AS SET

Please correct me if I am wrong......
Advertising a summary route without the AS info could cause a loop
because the receiving router might have one of it prefixes summarized,
so when it looses connection to this prefix, he may be tempted to use
this summary route which will result in a loop.

On 3/14/10, Muzammil Malick <malickmuz_at_gmail.com> wrote:
> Thanks
>
> but how could this cause a loop?
> If the local router has a more specific route to a destination that is
> covered by the summary then it will use that.
>
> R1 ----------- R2
>
> If R1 advertises 10.0.0.1/24 to R2 and then R2 advertises back a summary for
> 10.0.0.0/16 without AS info. R2 has now covered many other prefixes which
> may have come
> from other AS' and even the prefix from R1, however if R1 has more specific
> routes it will use these. If it doesn't have more specific info then this
> will be its only route anyway so
> how can a loop be formed?
>
>
>
> On 14 March 2010 19:21, Nadeem Rafi <nrafia_at_gmail.com> wrote:
>
>> If i am wrong please correct me.
>>
>> when bgp is summarized then information for the routes being summarized is
>> lost. And summarizing AS is considered to be originator of this new route.
>> All the AS afterwards dont have knowledge of routes being summarized that
>> from which AS they belong. And this can led from non-optimal routing to
>> routing loops, because of this as-set is used to feed with
>> more information about routes being summarized.
>>
>>
>>
>> HTH
>>
>> On Sun, Mar 14, 2010 at 10:12 PM, Muzammil Malick
>> <malickmuz_at_gmail.com>wrote:
>>
>>> Hi
>>>
>>> Could someone please help me out and explain why you would include AS
>>> information in a bgp summary (aggregate-address 10.0.0.0 255.255.0.0
>>> summary-only as-set)
>>>
>>> I know what it does and how to use it but why from a design perspective
>>> would you want to send AS information as apart of a summary.
>>> Can someone provide an example?
>>>
>>>
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