Does Fastmail use a child sticky resolver?

sebwills · 28 Feb 2016, 06:15 PM

Does anyone know whether the DNS resolver used by Fastmail's servers has 'child sticky' behaviour, as described here?

In other words, if I have changed the nameservers for a domain, but the old nameserver still claims to be authoritative (i.e. publishes NS records pointing to itself), when the appropriate TTL expires will Fastmail go back to the TLD nameserver and find the new nameserver for the domain, or will it go back to the old nameserver and keep using that since it still claims to be authoritative? (The latter is what 'child sticky' resolvers do)

BritTim · 28 Feb 2016, 07:11 PM

My understanding is that this behavior is not decided at the Fastmail end. It is the decision of the system doing the lookup as to which zone to query for the up to date records. IMHO, whatever the RFCs might say, to assume the name servers for a domain have not changed, and just to go to old ones willy-nilly just to avoid an extra lookup, goes against the spirit of domain resolution.

robn · 28 Feb 2016, 07:29 PM

I'd not heard of "child sticky" before. But no, we don't do that. Our DNS behaviour is entirely standard - if we have a cached record that hasn't expired yet (by time-to-live) we use it, otherwise we go looking for it. We'll use an NS record if we have it cached and it hasn't expired, but worst case, if everything has expired (or we never had it), we'll start at the root servers and work our way down.

sebwills · 29 Feb 2016, 12:34 AM

Thanks for the quick reply, Rob!

28 Feb 2016, 06:15 PM	#1
sebwills Junior Member Join Date: Jan 2015 Posts: 11	Does Fastmail use a child sticky resolver? Does anyone know whether the DNS resolver used by Fastmail's servers has 'child sticky' behaviour, as described here? In other words, if I have changed the nameservers for a domain, but the old nameserver still claims to be authoritative (i.e. publishes NS records pointing to itself), when the appropriate TTL expires will Fastmail go back to the TLD nameserver and find the new nameserver for the domain, or will it go back to the old nameserver and keep using that since it still claims to be authoritative? (The latter is what 'child sticky' resolvers do)

28 Feb 2016, 07:11 PM	#2
BritTim The "e" in e-mail Join Date: May 2003 Location: mostly in Thailand Posts: 3,095	My understanding is that this behavior is not decided at the Fastmail end. It is the decision of the system doing the lookup as to which zone to query for the up to date records. IMHO, whatever the RFCs might say, to assume the name servers for a domain have not changed, and just to go to old ones willy-nilly just to avoid an extra lookup, goes against the spirit of domain resolution.

28 Feb 2016, 07:29 PM	#3
robn Master of the @ Join Date: May 2012 Location: Melbourne, Australia Posts: 1,007 Representative of: Fastmail.fm	I'd not heard of "child sticky" before. But no, we don't do that. Our DNS behaviour is entirely standard - if we have a cached record that hasn't expired yet (by time-to-live) we use it, otherwise we go looking for it. We'll use an NS record if we have it cached and it hasn't expired, but worst case, if everything has expired (or we never had it), we'll start at the root servers and work our way down.

29 Feb 2016, 12:34 AM	#4
sebwills Junior Member Join Date: Jan 2015 Posts: 11	Thanks for the quick reply, Rob!