[Question] What is an accurate meaning of "A server MAY cache a dead server indication"?

[Hideshi Enokihara <Hideshi.Enokihara@jp.yokogawa.com>]

Hi all,

I want to confirm regarding the following RFC2308's description.

---------
7.2 Dead / Unreachable Server (OPTIONAL)

   Dead / Unreachable servers are servers that fail to respond in any
   way to a query or where the transport layer has provided an
   indication that the server does not exist or is unreachable.  A
   server may be deemed to be dead or unreachable if it has not
   responded to an outstanding query within 120 seconds.

   Examples of transport layer indications are:

      ICMP error messages indicating host, net or port unreachable.
      TCP resets
      IP stack error messages providing similar indications to those above.

   A server MAY cache a dead server indication.  If it does so it MUST
   NOT be deemed dead for longer than five (5) minutes.  The indication
   MUST be stored against query tuple <query name, type, class, server
   IP address> unless there was a transport layer indication that the
   server does not exist, in which case it applies to all queries to
   that specific IP address.
-----------

Last sentence says, "A server MAY cache a dead server indication.".
I think that "server" should be "resolver"(This "resolver" include a client that have caching function.) in this sentence.

Because section 7.1 says,
-----------

7.1 Server Failure (OPTIONAL)

   Server failures fall into two major classes.  The first is where a
   server can determine that it has been misconfigured for a zone.  This
   may be where it has been listed as a server, but not configured to be
   a server for the zone, or where it has been configured to be a server
   for the zone, but cannot obtain the zone data for some reason.  This
   can occur either because the zone file does not exist or contains
   errors, or because another server from which the zone should have
   been available either did not respond or was unable or unwilling to
   supply the zone.

   The second class is where the server needs to obtain an answer from
   elsewhere, but is unable to do so, due to network failures, other
   servers that don't reply, or return server failure errors, or
   similar.

   In either case a resolver MAY cache a server failure response.  If it
   does so it MUST NOT cache it for longer than five (5) minutes, and it
   MUST be cached against the specific query tuple <query name, type,
   class, server IP address>.
-------------

Last sentence use "a resolver".
This sentence indicate a server and a client with the caching function may cache a server failure response, right?

Is my understanding right?

Best Regards,
-- 
*************************************
Hideshi Enokihara
IPv6 Business
Network & Software Development Dept.
Yokogawa Electric Corporation

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