Propogation and Nameserver Management

Jeff Lasman blists at
Wed Jan 7 00:58:53 UTC 2004

On Tuesday 06 January 2004 02:15 pm, DiLu790 wrote:

> 1- If say I make the initial change one day, thus we can figure the
> propogation will take place 72 hours later or less.

"72 hours" was the name of a movie.  It's also based on some fact, 
though it's certainly not cut in stone.

What really happens is when you register a new nameserver (some 
registrars still call them 'hosts') the registrar takes anywhere from 
moments to hours to send the information to the top-level domain 
servers.  My guess is they do it sooner than later as there's no real 
reason for the information to sit around.

The top-level domain servers are reloaded on regular schedules; if my 
recollection is right it's at either 5pm or 5am (or both) either local 
time or GMT.  So all the changes wait until the reload.

If recollection serves the TTL on NS records is 2 days.  So the worst 
case will be about 72 hours, if the nameserver information is already 
in a cache on the local server looking it up.

If you're registering new nameservers, the 48 hours (2 days, or 172800 
seconds) doesn't matter, because there's nothing in the cache.

> BUT, what if
> during that time, I simply added an additional set of nameservers
> without changing what I have as the Primary and Secondary? Would that
> mean that my 72 hours begins from any point I update the infor
> regardless of whether the Primary and Secondary indicated remained
> the same?

You'll have four nameservers for the domain (they don't really come in 
sets).  Two of them will be giving out the old information, so anyone 
who uses them will see the old information and will look at the old 
IP#.  The other two will be giving out the new information, so anyone 
who uses them will see the new information and will end up using the 
new IP#.

The only way you can make the old nameservers not answer is to turn them 
off or if you can get the authoritative information removed from them.  
If you can turn them off or get the authoritative information removed 
from them, then you'll have reached your goal within 24 hours instead 
of within 72 hours.

However, the TTL on your own A records may also be set for two days or 

> 2- In #1 above, I make the assumption that you CAN have two sets of
> nameservers. One set being where your site was at previously and the
> other where you want your site to go (so's to avoid downtime).
> Would I be correct in my assumption.

You can have as many nameservers as you want.

When a system looks for an IP# for a site that's not already in it's 
cache, it first checks the top-level domain servers for all available 
nameservers.  It queries all of them.  It uses the first information it 
gets back and considers that nameserver as authoritative for the domain 
as long as the TTL isn't expired.

Jeff Lasman,, P. O. Box 52672, Riverside, CA  92517 US
Professional Internet Services & Support / Consulting / Colocation
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