Remove synchronous DNS name resolution

Change-Id: Ie5e670b769eb0674950f3679ef511047641c2873
Reviewed-on: https://code.wireshark.org/review/14751
Petri-Dish: João Valverde <j@v6e.pt>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Reviewed-by: Anders Broman <a.broman58@gmail.com>

3 files changed, 25 insertions, 25 deletions

diff --git a/docbook/release-notes.asciidoc b/docbook/release-notes.asciidoc
index 820959af91..f6f313326d 100644
--- a/docbook/release-notes.asciidoc
+++ b/docbook/release-notes.asciidoc
@@ -29,6 +29,11 @@ since version 2.0.0:
 the current capture file via the View menu in the Qt GUI.
 ** You can now show selected packet bytes as ASCII, HTML, Image, ISO 8859-1, Raw or UTF-8.
 ** You can now use regular expressions in Find Packet.
+** Name resolution for packet capture now supports asynchronous DNS lookups only. Therefore the
+"concurrent DNS resolution" preference has been deprecated and is a no-op. To enable DNS name
+resolution some build dependencies must be present (currently c-ares). If that is not the case DNS
+name resolution will be disabled (but other name resolution mechanisms, such as host files,
+are still available).
 
 //=== Removed Dissectors
 
diff --git a/docbook/wsug_src/WSUG_chapter_advanced.asciidoc b/docbook/wsug_src/WSUG_chapter_advanced.asciidoc
index 54ea191e4b..93e94b6c80 100644
--- a/docbook/wsug_src/WSUG_chapter_advanced.asciidoc
+++ b/docbook/wsug_src/WSUG_chapter_advanced.asciidoc
@@ -700,34 +700,30 @@ an abbreviated manufacturer name, which has been assigned by the IEEE (e.g.
 Try to resolve an IP address (e.g. 216.239.37.99) to something more ``human
 readable''.
 
-__DNS/concurrent DNS name resolution (system/library service)__: Wireshark will
-ask the operating system (or the concurrent DNS library), to convert an IP
-address to the hostname associated with it (e.g. 216.239.37.99 ->
-www.1.google.com). The DNS service is using synchronous calls to the DNS server.
-So Wireshark will stop responding until a response to a DNS request is returned.
-If possible, you might consider using the concurrent DNS library (which won't
-wait for a name server response).
+__DNS name resolution (system/library service)__: Wireshark will use a name
+resolver to convert an IP address to the hostname associated with it
+(e.g. 216.239.37.99 -> www.1.google.com).
+
+DNS name resolution can generally be performed synchronously or asynchronously.
+Both mechanisms can be used to convert an IP address to some human readable
+(domain) name. A system call like gethostname() will try to convert the address
+to a name. To do this, it will first ask the systems hosts file
+(e.g. __/etc/hosts__) if it finds a matching entry. If that fails, it will ask
+the configured DNS server(s) about the name.
+
+So the real difference between synchronous DNS and asynchronous DNS comes when
+the system has to wait for the DNS server about a name resolution. The system call
+gethostname() will wait until a name is resolved or an error occurs. If the DNS
+server is unavailable, this might take quite a while (several seconds).
 
 [WARNING]
 ====
-Enabling network name resolution when your name server is unavailable may
-significantly slow down Wireshark while it waits for all of the name server
-requests to time out. Always use concurrent DNS resolution.
+To provide acceptable performance Wireshark depends on
+an asynchronous DNS library to do name resolution. If one isn't available
+during compilation the feature will be unavailable.
 ====
 
-__DNS vs. concurrent DNS__: here's a short comparison: Both mechanisms are used
-to convert an IP address to some human readable (domain) name. The usual DNS
-call gethostname() will try to convert the address to a name. To do this, it
-will first ask the systems hosts file (e.g. __/etc/hosts__) if it finds a
-matching entry. If that fails, it will ask the configured DNS server(s) about
-the name.
-
-So the real difference between DNS and concurrent DNS comes when the system has
-to wait for the DNS server about a name resolution. The system call
-gethostname() will wait until a name is resolved or an error occurs. If the DNS
-server is unavailable, this might take quite a while (several seconds).
-
-The concurrent DNS service works a bit differently. It will also ask the DNS
+The asynchronous DNS service works a bit differently. It will also ask the DNS
 server, but it won't wait for the answer. It will just return to Wireshark in a
 very short amount of time. The actual (and the following) address fields won't
 show the resolved name until the DNS server returns an answer. As mentioned
diff --git a/docbook/wsug_src/WSUG_chapter_customize.asciidoc b/docbook/wsug_src/WSUG_chapter_customize.asciidoc
index 2abcfaab8b..9e0dd1a89f 100644
--- a/docbook/wsug_src/WSUG_chapter_customize.asciidoc
+++ b/docbook/wsug_src/WSUG_chapter_customize.asciidoc
@@ -287,8 +287,7 @@ Turns on name resolving for particular types of addresses and port numbers. The
 argument is a string that may contain the letters `m` to enable MAC address
 resolution, `n` to enable network address resolution, and `t` to enable
 transport-layer port number resolution. This overrides `-n` if both `-N` and
-`-n` are present. The letter `C` enables concurrent (asynchronous) DNS lookups.
-The letter `d` enables resolution from captured DNS packets.
+`-n` are present. The letter `d` enables resolution from captured DNS packets.
 
 -o <preference or recent settings>::