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❝Beating BGP is harder than we thought❞     (posted 2019-12-30)

In a paper for the HotNets'19, seven researchers admit that "beating BGP is harder than we thought". (Discovered through Aaron '0x88cc' Glenn.) The researchers looked at techniques used by big content delivery networks, including Google, Microsoft and Facebook, to deliver content to users as quickly as possible. This varies from using DNS redirects to PoPs (points of presence) close to the user, using BGP anycast to route requests to a PoP closeby and keeping data within the CDN's network as long as possible ("late exit" or "colt potato" routing).

Turns out, all this extra effort only manages to beat BGP as deployed on the public internet a small fraction of the time. So it's probably not really worth the effort. Also interesting: when BGP is worse, that's usually consistent over relatively long timescales, and when things deteriorate over one path, they tend to also get worse over alternative paths.

That seems strange, as the authors observe that "BGP, the Internet’s inter-domain routing protocol, is oblivious to performance and performance changes." However, BGP isn't deployed in a vacuum. People either install capacity where BGP is going to use it, or they tune BGP parameters to use capacity that's installed.

So having automated traffic management doesn't seem to help much—or does it? Maybe all paths deteriorate together because the automated traffic management solutions do their job and distribute the traffic equally over the available paths, keeping performance the same.

However, there are some cases when one of the options (regular BGP, anycast, late exit, DNS redirect) performs a lot poorer than the alternative(s). So it's probably more important to focus on avoiding really bad paths rather than trying to pick really good ones.

Also interesting: apparently ISPs rarely include the EDNS client subnet option, which DNS redirect really needs to work well. However, the Google and OpenDNS/Cisco public DNS services seem to do support it (but not CloudFlare), so if you're experiencing poor performance towards a CDN, you may want to try using the Google or OpenDNS DNS servers.

Download the paper here.

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