You can use the ultimate BOFH BGP tool, which is to include the network you don't want those announcements to go in the AS Path. Let's say your ASN is 65000, and the target you want to not route through that path is 65001.
For the path you want that network to route to, announce this AS Path: 65000 65000 65000 65000 65000 For the path you don't want that network to route to, announce this AS Path: 65000 65001 65000 So your announcements still have your AS as first AS and peer AS. But 65001 loop detection will kill that announcement, regardless of local preference or AS Path size. Rubens On Mon, Jan 22, 2024 at 9:50 AM William Herrin <b...@herrin.us> wrote: > > Howdy, > > Does anyone have suggestions for dealing with networks who ignore my > BGP route prepends? > > I have a primary ingress with no prepends and then several distant > backups with multiple prepends of my own AS number. My intention, of > course, is that folks take the short path to me whenever it's > reachable. > > A few years ago, Comcast decided it would prefer the 5000 mile, > five-prepend loop to the short 10 mile path. I was able to cure that > with a community telling my ISP along that path to not advertise my > route to Comcast. Today it's Centurylink. Same story; they'd rather > send the packets 5000 miles to the other coast and back than 10 miles > across town. I know they have the correct route because when I > withdraw the distant ones entirely, they see and use it. But this time > it's not just one path; they prefer any other path except the one I > want them to use. And Centurylink is not a peer of those ISPs, so > there doesn't appear to be any community I can use to tell them not to > use the route. > > I hate to litter the table with a batch of more-specifics that only > originate from the short, preferred link but I'm at a loss as to what > else to do. > > Advice would be most welcome. > > Regards, > Bill Herrin > > -- > William Herrin > b...@herrin.us > https://bill.herrin.us/
