On Mon, Jun 15, 2015 at 2:13 PM, Bill Woodcock <wo...@pch.net> wrote: > Or you could skip the MX records, and just put both US and European > SMTP servers on the same IP address, which would save a lot of > steps and simplify the system, but leave you with the _very_ > occasional corner-case of someone equal-path-length load-balancing > traffic to you such that half of one TCP session goes to Europe, and > half the the US. That’s a bogeyman that scares a lot of people into not > using anycast for TCP services, particularly long-lived ones, but it’s a > theoretical problem rather than an actually-observed-in-the-wild problem. > But since it scares people, it’s probably safer just doing the DNS > anycast, rather than SMTP anycast, to avoid startling the > easily-upset out there. :-)
If I had a dollar for every system that's collapsed from a known but previously "theoretical" problem... It's only theoretical until a VIP can't connect. Deploy a system without covering the corner cases and your comeuppance is assured. Okay, granted you can probably cover your corner case here with a priority 20 MX that leads to a unicast address on one of the two servers. SMTP can let the rare fellow with the bisected packet flow gracefully fall back. Nevertheless, I think you've offered some really bad advice here Bill. Hijackers killing the passengers was a bogeyman too. If you just kept calm and cooperated, you lived through it. Until you didn't, and allowed yourself to be an instrument in killing thousands on the ground as a bonus. Sometimes the math offers really bad advice. On Mon, Jun 15, 2015 at 2:28 PM, Nick Hilliard <n...@foobar.org> wrote: > On 15/06/2015 19:09, William Herrin wrote: >> Anycast + TCP = much pain, for reasons which should be obvious. > > This was presented at some conference or other a couple of years ago: > https://www.nanog.org/meetings/nanog37/presentations/matt.levine.pdf Thought the comment on page 22 was apropos: their plan is to be dead before future change catches up with them. Regards, Bill Herrin -- William Herrin ................ her...@dirtside.com b...@herrin.us Owner, Dirtside Systems ......... Web: <http://www.dirtside.com/>
