DDNS and cache interval concern

  • Thread starter Thread starter Louis
  • Start date Start date
L

Louis

Hello,

How to deal with DNS cache issue when a server that a
client is communicating with is using DDNS? i.e if the DNS
TTL is 15min, it is possible the client cannot communicate
with the server up to 15min.

Reducing the TTL interval seems help but it would
introduce lots more DNS query.

Another related question... when a client cannot reach a
server using a cached DNS info, will the client query the
DNS server again and if yes, is it on by default?

Thank you in advance!
Louis
 
TTL is 15min, it is possible the client cannot communicate
with the server up to 15min.
Click to expand...
Simply, the first time the client queries for that record, the DNS server
will respond with the record AND a flag that says "don't ask me about this
same record for the next 15 minutes"
The client will cache that info and whenever it needs the record again, it
will look at its cache. If you want the client to ask the server again for
that same record BEFORE the 15 minutes expire, you will have to clear the
client's resolver cache (ipconfig /flushdns or Net stop dnscache/net start
dnscache
Another related question... when a client cannot reach a
server using a cached DNS info, will the client query the
DNS server again and if yes, is it on by default?
Click to expand...
IF the client can not reach the DNS server, it will try another DNS server
(if multiple DNS servers are configured on the client). If the other DNS
server responds, then the client will from then start using this one that
responded AND it will then blacklist (ignore) the other DNS server that it
could not reach. I am not sure how long this "ignore" lasts, but as long as
the second DNS server is responding, the client will have no need to look at
the first.

--
Sincerely,

Dèjì Akómöláfé, MCSE MCSA MCP+I
www.akomolafe.com
www.iyaburo.com
Do you now realize that Today is the Tomorrow you were worried about
Yesterday? -anon
 
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