Netgear router not honoring DNS TTL?

Discussion in 'OT Technology' started by mdaniel, Apr 20, 2006.

  1. mdaniel

    mdaniel S is for Shiksa

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    I just worked on a project that required a hosting company to change a host (a) record to point to a different IP address. They use a TTL of 3600. Isn't that supposed to mean that DNS clients and servers won't cache it for more than an hour? Hours later, my router was still pointing me to the old IP address. For some reason I had my router listed as my 1st DNS sever. I rebooted it and it resolved the updated IP address. I did flush my PC's dns cache so I know its the router that was giving out the old IP address. Am I missing something or did Netgear just ignore the TTL?
     
  2. EvilSS

    EvilSS New Member

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    I assume the TTL was on the record before the change, yes?

    I would not be shocked if they were ignoring it. They (consumer router manufactures) don't always put a lot of thought into their design sometimes.
     
  3. P07r0457

    P07r0457 New Member

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    This *could* be the router, or it *could* be your ISP. Your client machines are querying the router for DNS records. The router is then querying your ISPs DNS servers as specified by DHCP. One of those two devices are "OVERthought" (unlike being not-so-thought-out, as someone mentioned)... One of those devices is ignoring the TTL, and this is why:

    Many ISPs and consumer routers are ignoring TTLs at the request of the industry. There are a lot of BAD admins out there, and they are abusing the TTL system. It used to be that you had a long TTL most of the time, then shortened it up a cycle before making a change to DNS, then once the change was made, the short TTL would mandate a refresh of their cache quickly, meaning less downtime. Once you changed the record(s) you would up the TTL back to it's normal value. People wern't doing this... And as a result, the DNS system became strained.

    If I had to guess, I'd say that it's your ISP that is the culprit. Your router is probably just acting as a "passthru".

    AOL was the first ISP to do this, that I know of... However it has filtered down to many other ISPs. Earthlink was infamous for this, as well.
     
  4. mdaniel

    mdaniel S is for Shiksa

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    As soon as I restarted the router and flushed my own cache, my ping resolved the correct IP address. Flushing my cache alone didn't change it. Also, when I reconfigured TCP/IP to hit the ISPs DNS servers instead of the router, I got the right IP.
     

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