What's the point of prepend communities?

Christopher Morrow morrowc.lists at gmail.com
Thu Oct 26 18:50:54 CST 2017


On Thu, Oct 26, 2017 at 2:47 PM, Jason Lixfeld <jason+nanog at lixfeld.ca>
wrote:

> Hi Bill,
>
> > On Oct 26, 2017, at 2:37 PM, William Herrin <bill at herrin.us> wrote:
> >
> > BGP routing is based on "distance". Distance in BGP is primarily
> calculated as the number of ASNs in the AS Path. Prepends make a path more
> distance, encouraging routers to choose a different path if one is
> available.
>
> I understand how prepends fit in the context of best path selection, but
> my question was more the difference between a customer signalling the ISP
> to prepend their AS using a BGP community stamped to a prefix vs. the
> customer prepending their own AS instead.
>
>
blame shifting?
avoiding instances where a third party filters:
  <ispasn> ?$
vs <ispasn> .*$

or just people's  particular picadellos.


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