Re:Cloudflare servers don't own IPs now, so how do they conn...
by toast0 on Friday November 25, 2022 @05:28PM
(#33747511)
Your intuition is more or less all wrong here, sorry.
Most routers with multiple viable paths pass was too much traffic to do state tracking of individual flows. Most typically, the default metric is BGP path length, for a given prefix, send packets through the route that has the most specific prefix, if there's a tie, use the route that transits the fewest networks to get there, if there's still a tie, use the route that has been up the longest (which maybe counts as state tracking). Routing like this doesn't take into account any sort of load metric, although people managing the routers might do traffic engineering to try to avoid overloaded routes (but it's difficult to see what's overloaded a few hops beyond your own router).
For the most part, an anycast operation is going to work best if all sites can handle all the forseable load, because it's easy to move all the traffic, but it's not easy to only move some. Everything you can do to try to move some traffic is likely to either not be effective or move too much.
Most routers with multiple viable paths pass was too much traffic to do state tracking of individual flows. Most typically, the default metric is BGP path length, for a given prefix, send packets through the route that has the most specific prefix, if there's a tie, use the route that transits the fewest networks to get there, if there's still a tie, use the route that has been up the longest (which maybe counts as state tracking). Routing like this doesn't take into account any sort of load metric, although people managing the routers might do traffic engineering to try to avoid overloaded routes (but it's difficult to see what's overloaded a few hops beyond your own router).
For the most part, an anycast operation is going to work best if all sites can handle all the forseable load, because it's easy to move all the traffic, but it's not easy to only move some. Everything you can do to try to move some traffic is likely to either not be effective or move too much.