>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 implemented that restriction).
The "set as-path prepend last-as" is a completely different story; it's used to do proxy prepending for your customers. Ivan Pepelnjak http://blog.ioshints.info > -----Original Message----- > From: Mikael Abrahamsson [mailto:swm...@swm.pp.se] > Sent: Friday, February 20, 2009 3:06 PM > To: nanog@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: swm...@swm.pp.se
