clarify slip doc

3643.	[doc]		Clarify RRL "slip" documentation.
(cherry picked from commit 2bae76022cbdf8a207d4c3982b589156e1a09e09)

diff --git a/CHANGES b/CHANGES
index 448c57ad8f4605fedbe199452058d03925d9449c..45582730ce5fedde666f962aae9c4d35fe13fabf 100644 (file)
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,5 @@
+3643.  [doc]           Clarify RRL "slip" documentation.
+
 3638.  [cleanup]       Add the ability to handle ENOPROTOOPT in case it is 
                        encountered. [RT #34668]
 

diff --git a/doc/arm/Bv9ARM-book.xml b/doc/arm/Bv9ARM-book.xml
index 219c505025c4b1a09e63de697ea2aec7dc593228..7a9619b26c89284009a5f5c782afef8d0912997e 100644 (file)
--- a/doc/arm/Bv9ARM-book.xml
+++ b/doc/arm/Bv9ARM-book.xml
@@ -9535,13 +9535,30 @@ ns.domain.com.rpz-nsdname   CNAME   .
            amplification, of "slipped" responses make them unattractive
            for reflection DoS attacks.
            <command>slip</command> must be between 0 and 10.
-           A value of 0 does not "slip";
-           no truncated responses are sent due to rate limiting.
+           A value of 0 does not "slip":
+           no truncated responses are sent due to rate limiting,
+           all responses are dropped.
+           A value of 1 causes every response to slip;
+           values between 2 and 10 cause every n'th response to slip.
            Some error responses including REFUSED and SERVFAIL
            cannot be replaced with truncated responses and are instead
            leaked at the <command>slip</command> rate.
          </para>
 
+         <para>
+           (NOTE: Dropped responses from an authoritative server may
+           reduce the difficulty of a third party successfully forging
+           a response to a recursive resolver. The best security
+           against forged responses is for authoritative operators
+           to sign their zones using DNSSEC and for resolver operators
+           to validate the responses. When this is not an option,
+           operators who are more concerned with response integrity
+           than with flood mitigation may consider setting
+           <command>slip</command> to 1, causing all rate-limited
+           responses to be truncated rather than dropped.  This reduces
+           the effectiveness of rate-limiting against reflection attacks.)
+         </para>
+
          <para>
            When the approximate query per second rate exceeds
            the <command>qps-scale</command> value,