The reason _why_ someone would filter as-path is for protection of error.
In many scenarios prepending is not necessary or preferred so usually
exact policy is set in place from a providers perspective to a customer.
You should always check and see what a providers policy is especially if
you are planning to do BGP tuning....
-blair
AT&T CERFnet
Backbone Engineering and Planning
| PGP Public Key: www.hfh.com/blair/pgp.txt |
On Tue, 19 Oct 1999, Vijay Gill wrote:
> On Tue, 19 Oct 1999, Steve Austin wrote:
>
> > Most likely UUnet is filtering out the prepended as-path. You may want to
> > contact them and check to see if they are allowing you to do this.
>
>
> Could you explain the reasoning as to _why_ anyone would filter out a
> prepended as-path?
>
>
> As for the original poster, how do you know your routes disappear? Are you
> using some sort of looking glass? What may be happening is that if you
> prepend enough times to UUNET, the path becomes unattractive, even
> internally, and all traffic starts to go over sprint. Since the UUNET
> path is no longer the best path for almost any router, and only the best
> path is propagated further, it may lead to a disappearance of the uunet
> path from looking glasses.
>
> /vijay
>
>
> > -Steve
> >
> > At 11:03 AM 10/19/99 -0400, Eric J Merkel wrote:
> > >
> > >We currently have 3 upstream T1's. 1 with UUNET and 2 with Sprint. Right now
> > >our UUNET T1(incoming traffic) is maxing out at 97% at night while our
> > >Sprint T1's are at about 40% (incoming traffic).
> > >
> > >I was trying to prepend our AS path to our announcements goint to UUNet to
> > >hopefully even things out but for some reason when doing this, all of our
> > >routes thru UUNET disappeared most likely to a misconfiguration on my part
> > >(I am a BGP newbie). I have since taken our the route-map statement and
> > >routes thru UUNET are visible again thru the DIGEX looking glass.
> > >
> > >Here are my UUnet neighbor statements:
> > >neighbor 137.39.2.108 remote-as 701
> > >neighbor 137.39.2.108 ebgp-multihop 2
> > >neighbor 137.39.2.108 update-source FastEthernet0/0
> > >neighbor 137.39.2.108 next-hop-self
> > >neighbor 137.39.2.108 route-map SETPATH out
> > >neighbor 137.39.2.108 filter-list 10 out
> > >
> > >ip as-path access-list 10 permit ^$
> > >
> > >access-list 1 permit 0.0.0.0
> > >
> > >route-map SETPATH permit 10
> > > match ip address 1
> > > set as-path prepend 13638 13638
> > >
> > >I have also tried it as such:
> > >route-map SETPATH permit 10
> > > match as-path 10
> > > set as-path prepend 13638 13638
> > >
> > >
> > >Anyone got any ideas? BTW I am doing a clear ip bgp 137.39.2.108 after the
> > >changes are complete. :)
> > >
> > >
> > >Eric Merkel / MetaLink Technologies, Inc
> > >~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
> > >Email: merkel@metalink.net
> > >Phone: 419-782-3472 X304
> > >~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
> > >
> > >
> >
> >
>
> Vijay Gill |The (paying) customer is always right.
> wrath@cs.umbc.edu, vijay@umbc.edu | - Piercarlo Grandi
> http://www.gl.umbc.edu/~vijay | Eagles may soar, but weasels don't get
> These are my opinions only. | sucked into jet engines.
>
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