On Thu, 12 Aug 2021, William Herrin wrote:
On Thu, Aug 12, 2021 at 9:41 AM Hank Nussbacher <hank@interall.co.il> wrote:
On 12/08/2021 17:59, William Herrin wrote:
If you prune the routes from the Routing Information Base instead, for any widely accepted size (i.e. /24 or shorter netmask) you break the Internet.
How does this break the Internet? I would think it would just result in sub-optimal routing (provided there is a covering larger prefix) but everything should continue to work. Clue me in, please.
A originates 10.0.0.0/16 to paid transit C B originates 10.0.1.0/24 also to paid transit C C offers both routes to D. D discards 10.0.1.0/24 from the RIB based on same-next-hop You peer with A and D. You receive only 10.0.0.0/16 since A doesn't originate 10.0.1.0/24 and D has discarded it. You send packets for 10.0.1.0/24 to A (the shortest path for 10.0.0.0/16), stealing A's paid transit to C to get to B. Unless A filters C-bound packets purportedly from 10.0.1.0/24. B doesn't currently transit for A so from B's perspective that's not an allowed path. In which case, your path to 10.0.1.0/24 is black holed.
D broke the Internet. If packets from you reach A at all, they do so through an unpermitted path.
A originated the /16 and should be prepared to deal with all bits to IPs within it. What's worse is when A originates/advertises the /16 to C. A also advertises the /24(s) only to other transits D, E, and F. C's peers that don't see the subnets send traffic to C that C then has to send out via transit to reach D, E, or F. I've been C :( We asked A to make it stop. ---------------------------------------------------------------------- Jon Lewis, MCP :) | I route StackPath, Sr. Neteng | therefore you are _________ http://www.lewis.org/~jlewis/pgp for PGP public key_________