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No-IP has a fixed TTL of 60 seconds for dynamic DNS host records set, DynDNS has a default TTL value of 60 seconds, changeip uses 30 seconds. However our DSL modem gets a DHCP lease time of 7200 seconds (2 hours):

DHCP WAN Client: bound, IP: 92.254.x.x, GW: 92.254.48.1, lease time: 7200

Why not have a larger TTL and preferable sync the remaining DHCP lease time value with the DynDNS TTL value. The No-IP updater protocol doesn't even allow to specify a TTL anywhere in a the update command. The Bind nsupdate9 on the contrary allows to specify a TTL on creating a new record (update add command).

Which are the free dynamic DNS services that allow updating the TTL in the the update command?

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You can't sync the DNS TTL value to anything, because DNS is typically employed in a tiered structure. Each DNS server starts its own TTL countdown after successfully querying upstream. That's why DDNS services usually use very short TTL values.

For n levels of DNS servers, the "worst overall TTL" is n * TTL. This happens when each server queries upstream at the very last moment of the upstream server's TTL countdown.

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  • This is a very old thread, but -- the TTL countdown is not restarted if the server responds from cache. Only the "authoritative" servers (tier 0) always reply with the full TTL value, but all "caching" tiers only reply with the remaining TTL since the record was entered to their local cache. So a record will never be cached for more than 1xTTL.
    – u1686_grawity
    Apr 14, 2020 at 13:26

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