nanog mailing list archives
Re: Anycast provider for SMTP?
From: "Joe Abley" <jabley () hopcount ca>
Date: Mon, 15 Jun 2015 14:58:05 -0400
Hi Joe, On 15 Jun 2015, at 13:50, Joe Hamelin wrote:
I have a mail system where there are two MX hosts, one in the US and one inEurope. Both have a DNS MX record metric of 10 so a bastardizedround-robin takes place. This does not work so well when one site goesdown. My solution will be to place a load balancer in a hosting site(virtual, of course) and have it provide HA. But what about HA for the LB? At first glance anycasting would seem to be a great idea but there isa problem of broken sessions when routes change. Have any of you seen something like this work in the wild?
If you can give responses to QTYPE=MX queries that match the location of the client, you can approximate this without deploying your SMTP servers using anycast. This feels like a simpler solution to operate; anycast sometimes pits BGP-fearing, syseng people against neteng people when things break at 3am, and if that rings true for you then a solution that avoids it might be of interest.
So, suppose clients in region A could query NETHEAD.COM/IN/MX and get a response that looks like
NETHEAD.COM. IN MX 10 REGION-A-MX.NETHEAD.COM. IN MX 20 REGION-B-MX.NETHEAD.COM. IN MX 20 REGION-C-MX.NETHEAD.COM.whereas clients in region B might see a response that looks more sensible to them:
NETHEAD.COM. IN MX 10 REGION-B-MX.NETHEAD.COM. IN MX 20 REGION-A-MX.NETHEAD.COM. IN MX 20 REGION-C-MX.NETHEAD.COM. etc, etc.That way you still get a reasonable fallback in the event that one MX target is unreachable for a particular client, but you steer the bulk of your traffic in a way that makes sense (and which your syseng people don't have to understand the details of).
You can achieve the above DNS trickery using various load balancers that other people in this thread have already mentioned. You can also install your own geomaps in your own nameservers and handle it yourself, or you can buy managed DNS service from various people that can do this kind of thing.
Disclaimer: Dyn, for whom I work, sells such a service. Joe
Current thread:
- Re: Anycast provider for SMTP?, (continued)
- Re: Anycast provider for SMTP? John Levine (Jun 15)
- Re: Anycast provider for SMTP? Bill Woodcock (Jun 16)
- Re: Anycast provider for SMTP? William Herrin (Jun 16)
- Re: Anycast provider for SMTP? Bill Woodcock (Jun 16)
- Re: Anycast provider for SMTP? Mark Andrews (Jun 16)
- Re: Anycast provider for SMTP? John Levine (Jun 16)
- Re: Anycast provider for SMTP? Masataka Ohta (Jun 16)
- Re: Anycast provider for SMTP? Owen DeLong (Jun 16)
- Re: Anycast provider for SMTP? Jon Lewis (Jun 16)
- Re: Anycast provider for SMTP? James Hartig (Jun 19)
- Re: Anycast provider for SMTP? Christopher Morrow (Jun 19)
- Re: Anycast provider for SMTP? Joe Abley (Jun 19)
- Re: Anycast provider for SMTP? Christopher Morrow (Jun 19)
- Re: Anycast provider for SMTP? Rob Seastrom (Jun 20)