Lots of prepends - AS20912 case
dhetzel at gmail.com
Fri Feb 20 15:56:56 UTC 2009
If we really want bgp for idiots, perhaps a checkbox for "make this
(slightly,more,greatly) less preferred for incoming traffic" would do the
Then again, perhaps people who want the results of their local configuration
distributed to the ends of the earth should at least read a book or two...
On Fri, Feb 20, 2009 at 10:35 AM, Ivan Pepelnjak <ivan.pepelnjak at zaplana.net
> >From the end-user perspective, it makes sense to make the "prepend"
> parameter an integer. The only thing an end-user really needs is routing
> policy (primary/backup selection) and sometimes AS path prepending is the
> only solution. Allowing them to insert third-party AS numbers into the AS
> path increases their confusion (assuming they were never exposed to Cisco
> IOS). Obviously, the number of prepends has to be limited to something
> sensible (10 seems a good number, and it looks like Mikrotik has
> that restriction).
> The "set as-path prepend last-as" is a completely different story; it's
> to do proxy prepending for your customers.
> Ivan Pepelnjak
> > -----Original Message-----
> > From: Mikael Abrahamsson [mailto:swmike at swm.pp.se]
> > Sent: Friday, February 20, 2009 3:06 PM
> > To: nanog at nanog.org
> > Subject: Re: Lots of prepends - AS20912 case
> > On Fri, 20 Feb 2009, Dorn Hetzel wrote:
> > > Replacing what is conventially thought to be a string with
> > an integer
> > > multiplier seems a massive violation of the principle of
> > least astonishment.
> > On a Cisco running 12.0S:
> > route-map test1
> > set as-path prepend last-as ?
> > <1-10> number of last-AS prepends
> > Cisco seems to be doing more sensible limits, but I do agree
> > that the feature makes sense.
> > There are two ways of handling when someone puts in a very
> > high number to number of prepends:
> > 1. Say "out of limit" and disallow it in the config checker.
> > 2. Actually prepend the number of times specified.
> > The option done here:
> > 3. Prepend number of times entered modulo 256, is just broken.
> > --
> > Mikael Abrahamsson email: swmike at swm.pp.se
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