Add text describing the changes done in the MR in more detail

diff --git a/CHANGES b/CHANGES
index e355fb9b829b6039965b2bd047f1cc2c36bc8fea..4c53f9985277ed2d40cc0309d61c68f9a90ec8c7 100644 (file)
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,8 @@
+5516.  [func]          The default EDNS buffer size has been changed from 4096
+                       to 1232, the EDNS buffer size probing has been removed
+                       and ``named`` now sets the DON'T FRAGMENT flag on
+                       outgoing UDP packets. [GL #2183]
+
 5515.  [func]          Add 'rndc dnssec -rollover' command to trigger a
                        manual rollover for a specific key. [GL #1749]
 

diff --git a/doc/arm/reference.rst b/doc/arm/reference.rst
index 349de3220c72f8d9119db8f1b2c7bdb67a6eb434..f72c4c2f38797b2c930a792a852b6dc1d1645b56 100644 (file)
--- a/doc/arm/reference.rst
+++ b/doc/arm/reference.rst
@@ -3414,6 +3414,16 @@ Tuning
    dropping patterns, the query is retried over TCP.  Per-server EDNS statistics
    are only retained in memory for the lifetime of a given server's ADB entry.
 
+   The ``named`` now sets the DON'T FRAGMENT flag on outgoing UDP packets.
+   According to the measurements done by multiple parties this should not be
+   causing any operational problems as most of the Internet "core" is able to
+   cope with IP message sizes between 1400-1500 bytes, the 1232 size was picked
+   as a conservative minimal number that could be changed by the DNS operator to
+   a estimated path MTU minus the estimated header space. In practice, the
+   smallest MTU witnessed in the operational DNS community is 1500 octets, the
+   Ethernet maximum payload size, so a a useful default for maximum DNS/UDP
+   payload size on **reliable** networks would be 1400.
+
    Any server-specific ``edns-udp-size`` setting has precedence over all
    the above rules.
 

diff --git a/doc/notes/notes-current.rst b/doc/notes/notes-current.rst
index 03baa1660a2e197764c7c40e7622adda06bdfe3f..aa3f0b3a4612164997ae051bf34dc28caed741d1 100644 (file)
--- a/doc/notes/notes-current.rst
+++ b/doc/notes/notes-current.rst
@@ -24,8 +24,6 @@ Known Issues
 New Features
 ~~~~~~~~~~~~
 
-- None.
-
 - Add a new ``rndc`` command, ``rndc dnssec -rollover``, which triggers
   a manual rollover for a specific key. [GL #1749]
 
@@ -42,7 +40,17 @@ Removed Features
 Feature Changes
 ~~~~~~~~~~~~~~~
 
-- None.
+- [DNS Flag Day 2020]: The default EDNS buffer size has been changed from 4096
+  to 1232, the EDNS buffer size probing has been removed and ``named`` now sets
+  the DON'T FRAGMENT flag on outgoing UDP packets.  According to the
+  measurements done by multiple parties this should not be causing any
+  operational problems as most of the Internet "core" is able to cope with IP
+  message sizes between 1400-1500 bytes, the 1232 size was picked as a
+  conservative minimal number that could be changed by the DNS operator to a
+  estimated path MTU minus the estimated header space. In practice, the smallest
+  MTU witnessed in the operational DNS community is 1500 octets, the Ethernet
+  maximum payload size, so a a useful default for maximum DNS/UDP payload size
+  on reliable networks would be 1400. [GL #2183]
 
 Bug Fixes
 ~~~~~~~~~