Caching-Only Name Server down

[Barry Margolin]

In article <9n95hv$9up at pub3.rc.vix.com>,  <amran at isp.time.net.my> wrote:
>I'm deciding to add a Caching-Only Name Server. 
>All the Primary and Secondary servers then will point to the Caching-Only
>Name Server.
>The purpose is to improve the resolving processes for the remote domains. 

It's not too clear what you mean by this.  "Primary and secondary servers"
usually refer to different types of authoritative servers, these days
called master and slave servers.

It sounds like you're using these terms to refer to the servers that users
put in their /etc/resolv.conf or DNS Search Order; these should *also* be
caching servers.  And you're going to configure them all to use a
"forwarders" statement that points to a central caching-only server.  Is
this what you mean?

>Questions :
>1) If the Caching-Only server down, what will happened to my Primary and
>Secondary servers?
>Are they still can do the resolving processes? Can all the DNS clients which
>point to the these Primary/Secondary servers surf the Internet ?

It depends on whether you configure the servers with "forward first" (the
default) or "forward only".  If you use "forward first", then if the
central server is down they'll perform the query themselves.  However, this
will cause a delay in *every* lookup for an uncached name until the central
server is fixed, because they only know that the central server is down by
timing out waiting for a reply.  In the mean time the client may time out
and try his secondary server, which will then query the central server, and
then wait for a timeout.

For this reason, using a hierarchy of forwarders is generally not
recommended.  The benefit of the central cache is not very great, and the
problems caused by this single point of failure can be severe.

-- 
Barry Margolin, barmar at genuity.net
Genuity, Woburn, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.