Question about AS Origin changes

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1

Hi NANOG list,

I am wondering if anyone can give me possible reasons for some uncommon BGP
origin change activity. What we see is that sometimes the origin for a
prefix seems to change from a customer AS to it upstream provider and back.
In many instances the prefix simply switches back and forth for hours or
even days and sometimes very rapidly . Below I’m including an example of
some of the activities I see.

Prefix 202.83.96/20 on border router 154.11.98.225(AS 852)

At 14:10:56 Dec 04 2010, the BGP path with AS18106 as the origin
At 14:11:57, the BGP path with AS9255 as the origin
At 14:14:27, the BGP path with AS18106 as the origin.

Thanks,
Yaoqing

2

* Yaoqing Liu:

I am wondering if anyone can give me possible reasons for some uncommon BGP
origin change activity. What we see is that sometimes the origin for a
prefix seems to change from a customer AS to it upstream provider and back.
In many instances the prefix simply switches back and forth for hours or
even days and sometimes very rapidly . Below I’m including an example of
some of the activities I see.

This is expected if the upstream has a static route for the prefix (or
a route which redistributed from another routing protocol). This
could be a leftover from a non-BGP setup with the customer. Or this
could be some sort of backup procedure (perhaps prompted by the
instability of the BGP link).