nanog mailing list archives
Re: Consistent routing policy?
From: Owen DeLong <owen () delong com>
Date: Mon, 16 Sep 2019 12:04:08 -0700
For any router which receives both announcements, longest match always wins over all other BGP tie-breaking criteria. This is almost always summarized as “Longest Match always wins” because virtually any engineer recognizes that the winner is selected only from the available contestants, not from unknown distant contestants not present at the router in question. Owen
On Sep 16, 2019, at 11:26 , Töma Gavrichenkov <ximaera () gmail com> wrote: Peace, On Mon, Sep 16, 2019, 6:06 AM Mark Tinka <mark.tinka () seacom mu <mailto:mark.tinka () seacom mu>> wrote: Longest match always wins... so provided your /22's are in the global table, traffic will follow the path toward them before the /21 is preferred. Not always. E.g. imagine an ISP who has two connections to the outside world: one through a major ISP and the other through an IX. Such an ISP would be quite inclined both financially and technically to import routes just from the IX and set the default to the upstream ISP link. Therefore, an advertisement from the IX would always win no matter the length. There are more complicated cases as well. -- Töma
Current thread:
- Consistent routing policy? Ben Logan (Sep 16)
- Re: Consistent routing policy? Mark Tinka (Sep 16)
- Re: Consistent routing policy? Ben Logan (Sep 16)
- Re: Consistent routing policy? Mark Tinka (Sep 16)
- Re: Consistent routing policy? Ben Logan (Sep 16)
- Re: Consistent routing policy? Arie Vayner (Sep 16)
- Re: Consistent routing policy? Martijn Schmidt via NANOG (Sep 16)
- Re: Consistent routing policy? Ross Tajvar (Sep 16)
- Re: Consistent routing policy? Niels Bakker (Sep 16)
- Re: Consistent routing policy? Ben Logan (Sep 16)
- Re: Consistent routing policy? Mark Tinka (Sep 16)
- Re: Consistent routing policy? Töma Gavrichenkov (Sep 16)
- Re: Consistent routing policy? Owen DeLong (Sep 16)
- Re: Consistent routing policy? Töma Gavrichenkov (Sep 16)
- Re: Consistent routing policy? Mark Tinka (Sep 17)
- Re: Consistent routing policy? Mark Tinka (Sep 17)