Nathan Ward nanog at
Sun May 10 05:59:31 CDT 2009

On 10/05/2009, at 10:51 PM, yangyang. wang wrote:

> As we know, BGP instance running on routers don't allow loop in
> ASPATH, why they can be seen in RIBs? It's some particular technical
> configuration in practice? OR What's wrong with AS3130??

Look at the WHOIS entry for AS3130, and notice in the comments field:

"Regarding strange announcements by AS 3130 of prefixes in" is in the big headings on the top of that page.

He is no doubt announcing it with an origin AS of 3130 so no person or  
router complains about inconsistent origins.

Nathan Ward

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