6 ms·

TL;DR: You have a fine point to test a new domain's resolving status using dig +trace to not poison your cache. Existing domains need not apply. You may need

• rawrly 15y ago
  This is actually sadly exactly what the author missed in their article. DNS propagation is directly controlled by the TTL setting on a domain entry. TTL stands for Time To Live, this is the number (in seconds) that the DNS entry tells people to keep it active in the DNS server cache's (presuming the DNS server will not over-ride this for either a higher or lower number, which is entirely their choice but not common.) This is done so that any request to adomain.com will not have to require a DNS lookup to the main serve for every page request. It is true that if you have not done a lookup on the domain, then your computer and DNS servers would presumably not have any active DNS records for the domain. So you can make a change and "viola" within 5 minutes (the next time you visit the site) you will have the updated record. However, if you had recently done a DNS inquiry and eceived the record for the old DNS entry, you will need to wait for the old DNS entry to expire before the DNS server you are using will choose to look it up again. This doesn't go into any of the fun of what happens when you have 2 or more DNS servers setup, but ultimately what people are seeing is that the "48 hour" waiting period is substantially less, however most ISPs will stick to this default number to reduce worrisome support from their clients who think otherwise but don't know anything about how DNS works so support will never be able to explain this in laymen terms (or wait, did I just do that?)
  • seanp2k2 15y ago
    me: web hosting sysadmin also dealing with clients. Yes, people really do freak out about DNS problems, and we quote 72 hours because we have clients on 6 continents. Realistically, it takes 30 minutes - 4 hours for DNS updates to stick. Use http://host-tracker.com/ http://host-tracker.com/ to check the IP of your site -- that's what we do. It tests something like 80 locations, and the results show the IP returned. You are absolutely correct regarding the TTLs, and although I've seen well-intentioned help articles suggesting things like setting your TTL to 10-300 seconds...most "big" recursive resolvers will ignore TTLs below 3600 seconds (1 hour), so this doesn't really help. Props to anyone who knows what RFC covers this behaviour and cites a minimum valid TTL. I'm not aware of any, but I'm not totally up on my RFCs :)
    • rada 15y ago
      http://www.ietf.org/rfc/rfc1034.txt http://www.ietf.org/rfc/rfc1034.txt: The TTL is assigned by the administrator for the zone where the data originates. While short TTLs can be used to minimize caching, and a zero TTL prohibits caching, the realities of Internet performance suggest that these times should be on the order of days for the typical host. If a change can be anticipated, the TTL can be reduced prior to the change to minimize inconsistency during the change, and then increased back to its former value following the change. and http://www.ietf.org/rfc/rfc1912.txt http://www.ietf.org/rfc/rfc1912.txt: 1-5 days are typical values.
    • fuddie 15y ago
      Please provide further detail on these '"big" recursive resolvers' that ignore TTLs. I'm yet to see one in the wild and so I'm somewhat dubious of the claim. (Please don't be vague - post the addresses of the resolvers in question.)
      • jaylevitt 15y ago
        We just moved our DNS from Network Solutions to Route 53 this month, and I can verify that there are indeed resolvers that'll ignore TTLs. Ours were 3-6 hours, but it took some sites about 24 hours to pick up our new SOA. Which would have been fine - the A records were the same - but no, NetSol instantly starts serving a blank "Business Profile" landing page A-record. Thanks, people who used to run the Internet. I know one such caching server was ns1.dns.rcn.net. (But only from inside RCN; querying it from Comcast gave different results. Same IP address, so I'm assuming it's anycast.) whatsmydns.net reported others as "Bell South" and "Cox" (I can't recall the locations, I think one was in Georgia).
• SLuijk 15y ago
  I was not expecting so much traffic. I kicked in a few more gunicorn instances. Hope that helps. Well thats the point of using the -trace option. It makes dig act as the resolver bypassing all of the caches.
  • LogicX 15y ago
    My apologies - I glossed over your explanation of trace, as I've used it for years for other purposes, without the primary intention being this. expunging my other resolver rants from my OP