3 ms·

> If a server can ping, it can update its DNS record Isn't there a significant delay for this to propagate? > consumer WAN access can't be 5 nines guaranteed

by flukus 7y ago

> If a server can ping, it can update its DNS record Isn't there a significant delay for this to propagate? > consumer WAN access can't be 5 nines guaranteed 2 nines are more than sufficient, plus the occasional longer term outage for various network outages. Even for most business 5 nines isn't that important. > practical problem no 2 is that if your residential ISP sees activity on the standard SMTP ports Weirdly enough this isn't a problem for my ISP, I couldn't buy a static IP but they're happy to open any ports I want. YMMV.

Symbiote 7y ago
You set the DNS TTL to 30 or 60 seconds, then there's no problem with caching the old IP. Email is extremely tolerant of downtime. There are also commercial backup mail servers (these accept and cache the email until your server is back up), which can be used as the only public way to receive email. Some will deliver it to a non-standard port.
- krageon 7y ago
  > You set the DNS TTL to 30 or 60 seconds, then there's no problem with caching the old IP. This will not work. Most of your visitors will depend on some upstream resolver (for example google's resolver), which will cache you for 24h (you can explicitly request a flush - but the whole point of this system is that it's automated). AFAIK (which is a year or two out of date), every big DNS resolver that you might expect someone to use does this, to prevent the enormous performance issues from people setting their TTL to anything less than that. Edit: Of course if you use a good relay server that isn't owned by you you can mitigate this, because they'll keep the emails in a queue for you until you can be found again.
  - Symbiote 7y ago
    I haven't generally seen evidence of this when I've changed the IP address of websites. After the TTL expires, the only hits left on the old IP are from China (Great Firewall?).
  - jjeaff 7y ago
    Years ago, 24 to 48 hrs was the case for a DNS resolution update. But I have redirected DNS many times over the last few years and it resolves correctly, worldwide within a few minutes. Almost everytime. Occasionally, I will see a few locations in India or China cache for longer than the ttl but never longer than 4 to 6 hours. And this isn't just a record cache. Even a nameserver change seems to get picked up in less than 15 minutes worldwide.

by flukus 7y ago

Symbiote 7y ago

You set the DNS TTL to 30 or 60 seconds, then there's no problem with caching the old IP. Email is extremely tolerant of downtime. There are also commercial backup mail servers (these accept and cache the email until your server is back up), which can be used as the only public way to receive email. Some will deliver it to a non-standard port.

krageon 7y ago
> You set the DNS TTL to 30 or 60 seconds, then there's no problem with caching the old IP. This will not work. Most of your visitors will depend on some upstream resolver (for example google's resolver), which will cache you for 24h (you can explicitly request a flush - but the whole point of this system is that it's automated). AFAIK (which is a year or two out of date), every big DNS resolver that you might expect someone to use does this, to prevent the enormous performance issues from people setting their TTL to anything less than that. Edit: Of course if you use a good relay server that isn't owned by you you can mitigate this, because they'll keep the emails in a queue for you until you can be found again.
- Symbiote 7y ago
  I haven't generally seen evidence of this when I've changed the IP address of websites. After the TTL expires, the only hits left on the old IP are from China (Great Firewall?).
- jjeaff 7y ago
  Years ago, 24 to 48 hrs was the case for a DNS resolution update. But I have redirected DNS many times over the last few years and it resolves correctly, worldwide within a few minutes. Almost everytime. Occasionally, I will see a few locations in India or China cache for longer than the ttl but never longer than 4 to 6 hours. And this isn't just a record cache. Even a nameserver change seems to get picked up in less than 15 minutes worldwide.