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>

20 files changed, 90 insertions, 258 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index cd288e208c..118e5f97ea 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -879,9 +879,8 @@ if(HAVE_LIBCARES)
 	set(HAVE_C_ARES 1)
 endif()
 if(NOT HAVE_LIBCARES)
-	# We should make this an error at some point.
 	message(WARNING "Not using c-ares.")
-	message(WARNING "Synchronous name resolution can seriously degrade performance.")
+	message(WARNING "DNS name resolution for captures will be disabled.")
 endif()
 if(HAVE_LIBNL AND HAVE_AIRPCAP)
 	message(ERROR "Airpcap and Libnl support are mutually exclusive")
diff --git a/ConfigureChecks.cmake b/ConfigureChecks.cmake
index be9511e85b..d04c61b17a 100644
--- a/ConfigureChecks.cmake
+++ b/ConfigureChecks.cmake
@@ -105,8 +105,7 @@ check_symbol_exists("lrint"  "math.h"    HAVE_LRINT)
 cmake_pop_check_state()
 
 check_function_exists("getaddrinfo"      HAVE_GETADDRINFO)
-check_function_exists("gethostbyname"    HAVE_GETHOSTBYNAME)
-check_function_exists("gethostbyname2"   HAVE_GETHOSTBYNAME2)
+
 check_function_exists("getopt_long"      HAVE_GETOPT_LONG)
 if(HAVE_GETOPT_LONG)
 	if(HAVE_GETOPT_H)
diff --git a/cmakeconfig.h.in b/cmakeconfig.h.in
index b979bfca89..70601cc4f9 100644
--- a/cmakeconfig.h.in
+++ b/cmakeconfig.h.in
@@ -88,12 +88,6 @@
 /* Define to 1 if you have the `getaddrinfo' function. */
 #cmakedefine HAVE_GETADDRINFO 1
 
-/* Define to 1 if you have the `gethostbyname' function. */
-#cmakedefine HAVE_GETHOSTBYNAME 1
-
-/* Define to 1 if you have the `gethostbyname2' function. */
-#cmakedefine HAVE_GETHOSTBYNAME2 1
-
 /* Define to 1 if you have the getopt_long function. */
 #cmakedefine HAVE_GETOPT_LONG 1
 
diff --git a/configure.ac b/configure.ac
index 4217f29ec6..b83db53280 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2628,9 +2628,6 @@ else
 fi
 AC_SUBST(C_ARES_LIBS)
 
-# Check for synchronous name resolvers
-AC_CHECK_FUNCS([getaddrinfo gethostbyname gethostbyname2])
-
 dnl GEOIP Check
 GEOIP_LIBS=''
 AC_MSG_CHECKING(whether to use the GeoIP IP address mapping library if available)
@@ -2715,6 +2712,8 @@ AC_C_BIGENDIAN
 # XXX - do we need this?
 AC_PROG_GCC_TRADITIONAL
 
+AC_CHECK_FUNCS([getaddrinfo])
+
 AC_CHECK_FUNC(getopt_long,
   [
     GETOPT_LO=""
@@ -3354,8 +3353,7 @@ fi
 if test "x$have_good_c_ares" = "xyes" ; then
 	c_ares_message="yes"
 else
-	# We should make this an error at some point.
-	c_ares_message="no. This can cause serious performance issues."
+	c_ares_message="no (name resolution will be disabled)"
 fi
 
 if test "x$have_good_libcap" = "xyes" ; then
diff --git a/doc/rawshark.pod b/doc/rawshark.pod
index be8f680c17..75c93b918e 100644
--- a/doc/rawshark.pod
+++ b/doc/rawshark.pod
@@ -170,8 +170,6 @@ resolution
 
 B<t> to enable transport-layer port number resolution
 
-B<C> to enable concurrent (asynchronous) DNS lookups
-
 B<d> to enable resolution from captured DNS packets
 
 =item -o  E<lt>preferenceE<gt>:E<lt>valueE<gt>
diff --git a/doc/tshark.pod b/doc/tshark.pod
index 0ba3743461..fb88d53d9a 100644
--- a/doc/tshark.pod
+++ b/doc/tshark.pod
@@ -575,8 +575,6 @@ are turned on.
 
 The argument is a string that may contain the letters:
 
-B<C> to enable concurrent (asynchronous) DNS lookups
-
 B<d> to enable resolution from captured DNS packets
 
 B<m> to enable MAC address resolution
diff --git a/doc/wireshark.pod.template b/doc/wireshark.pod.template
index aebb2daf95..90f11dffe6 100644
--- a/doc/wireshark.pod.template
+++ b/doc/wireshark.pod.template
@@ -475,8 +475,6 @@ resolution
 
 B<t> to enable transport-layer port number resolution
 
-B<C> to enable concurrent (asynchronous) DNS lookups
-
 B<d> to enable resolution from captured DNS packets
 
 =item -o  E<lt>preference/recent settingE<gt>
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>::
 
diff --git a/epan/addr_resolv.c b/epan/addr_resolv.c
index ec3a7df9b3..7d541c29d2 100644
--- a/epan/addr_resolv.c
+++ b/epan/addr_resolv.c
@@ -284,7 +284,6 @@ e_addr_resolve gbl_resolv_flags = {
     TRUE,   /* mac_name */
     FALSE,  /* network_name */
     FALSE,  /* transport_name */
-    TRUE,   /* concurrent_dns */
     TRUE,   /* dns_pkt_addr_resolution */
     TRUE,   /* use_external_net_name_resolver */
     FALSE,  /* load_hosts_file_from_profile_only */
@@ -318,7 +317,6 @@ gchar *g_pvlan_path     = NULL;     /* personal vlans file    */
  * ares_gethostbyaddr().
  * The callback processes the response, then frees the request.
  */
-#define ASYNC_DNS
 typedef struct _async_dns_queue_msg
 {
     union {
@@ -343,9 +341,7 @@ static void c_ares_ghba_cb(void *arg, int status, int timeouts _U_, struct hoste
 
 ares_channel ghba_chan; /* ares_gethostbyaddr -- Usually non-interactive, no timeout */
 ares_channel ghbn_chan; /* ares_gethostbyname -- Usually interactive, timeout */
-#endif /* HAVE_C_ARES */
 
-#ifdef ASYNC_DNS
 static  gboolean  async_dns_initialized = FALSE;
 static  guint       async_dns_in_flight = 0;
 static  GList    *async_dns_queue_head = NULL;
@@ -361,7 +357,7 @@ add_async_dns_ipv4(int type, guint32 addr)
     msg->addr.ip4 = addr;
     async_dns_queue_head = g_list_append(async_dns_queue_head, (gpointer) msg);
 }
-#endif /* ASYNC_DNS */
+#endif /* HAVE_C_ARES */
 
 typedef struct {
     guint32      mask;
@@ -798,69 +794,29 @@ host_lookup(const guint addr)
          */
         tp = new_ipv4(addr);
         g_hash_table_insert(ipv4_hash_table, GUINT_TO_POINTER(addr), tp);
-    } else {
-        if ((tp->flags & DUMMY_AND_RESOLVE_FLGS) == DUMMY_ADDRESS_ENTRY) {
-            /*
-             * This hasn't been resolved yet, and we haven't tried to
-             * resolve it already, so try.
-             */
-            goto try_resolv;
-        }
+    } else if ((tp->flags & DUMMY_AND_RESOLVE_FLGS) != DUMMY_ADDRESS_ENTRY) {
         return tp;
     }
 
-try_resolv:
-    if (gbl_resolv_flags.network_name && gbl_resolv_flags.use_external_net_name_resolver) {
-        tp->flags |= TRIED_RESOLVE_ADDRESS;
-
-#ifdef ASYNC_DNS
-        if (gbl_resolv_flags.concurrent_dns &&
-                name_resolve_concurrency > 0 &&
-                async_dns_initialized) {
-            add_async_dns_ipv4(AF_INET, addr);
-            fill_dummy_ip4(addr, tp);
-            return tp;
-        }
+    /*
+     * This hasn't been resolved yet, and we haven't tried to
+     * resolve it already.
+     */
 
-        /*
-         * The Windows "gethostbyaddr()" insists on translating 0.0.0.0 to
-         * the name of the host on which it's running; to work around that
-         * botch, we don't try to translate an all-zero IP address to a host
-         * name.
-         *
-         * Presumably getaddrinfo() behaves the same way.  Anyway, we should
-         * never get to this code on Windows since those builds include c-ares.
-         */
-#elif defined(HAVE_GETADDRINFO)
-        if (addr != 0) {
-            struct sockaddr_in sin;
-
-            memset(&sin, 0, sizeof(sin));
-            sin.sin_family      = AF_INET;
-            sin.sin_addr.s_addr = addr;
-            if (getnameinfo((struct sockaddr *)&sin, sizeof(sin),
-                            tp->name, sizeof(tp->name),
-                            NULL, 0, NI_NAMEREQD) == 0) {
-                return tp;
-            }
-        }
-#elif defined(HAVE_GETHOSTBYNAME)
-        if (addr != 0) {
-            struct hostent *hostp;
+    fill_dummy_ip4(addr, tp);
+    if (!gbl_resolv_flags.network_name)
+        return tp;
 
-            hostp = gethostbyaddr((const char *)&addr, 4, AF_INET);
+    if (gbl_resolv_flags.use_external_net_name_resolver) {
+        tp->flags |= TRIED_RESOLVE_ADDRESS;
 
-            if (hostp != NULL && hostp->h_name[0] != '\0') {
-                g_strlcpy(tp->name, hostp->h_name, MAXNAMELEN);
-                return tp;
-            }
+#ifdef HAVE_C_ARES
+        if (async_dns_initialized && name_resolve_concurrency > 0) {
+            add_async_dns_ipv4(AF_INET, addr);
         }
 #endif
-
-        /* unknown host or DNS timeout */
     }
 
-    fill_dummy_ip4(addr, tp);
     return tp;
 
 } /* host_lookup */
@@ -884,10 +840,6 @@ host_lookup6(const struct e_in6_addr *addr)
     hashipv6_t * volatile tp;
 #ifdef HAVE_C_ARES
     async_dns_queue_msg_t *caqm;
-#elif defined(HAVE_GETADDRINFO)
-    struct sockaddr_in6 sin6;
-#elif defined(HAVE_GETHOSTBYNAME)
-    struct hostent *hostp;
 #endif
 
     tp = (hashipv6_t *)g_hash_table_lookup(ipv6_hash_table, addr);
@@ -902,54 +854,31 @@ host_lookup6(const struct e_in6_addr *addr)
         tp = new_ipv6(addr);
         memcpy(addr_key, addr, 16);
         g_hash_table_insert(ipv6_hash_table, addr_key, tp);
-    } else {
-        if ((tp->flags & DUMMY_AND_RESOLVE_FLGS) == DUMMY_ADDRESS_ENTRY) {
-            /*
-             * This hasn't been resolved yet, and we haven't tried to
-             * resolve it already, so try.
-             */
-            goto try_resolv;
-        }
+    } else if ((tp->flags & DUMMY_AND_RESOLVE_FLGS) != DUMMY_ADDRESS_ENTRY) {
         return tp;
     }
 
-try_resolv:
-    if (gbl_resolv_flags.network_name &&
-            gbl_resolv_flags.use_external_net_name_resolver) {
+    /*
+     * This hasn't been resolved yet, and we haven't tried to
+     * resolve it already.
+     */
+
+    fill_dummy_ip6(tp);
+    if (!gbl_resolv_flags.network_name)
+        return tp;
+
+    if (gbl_resolv_flags.use_external_net_name_resolver) {
         tp->flags |= TRIED_RESOLVE_ADDRESS;
 #ifdef HAVE_C_ARES
-        if ((gbl_resolv_flags.concurrent_dns) &&
-                name_resolve_concurrency > 0 &&
-                async_dns_initialized) {
+        if (async_dns_initialized && name_resolve_concurrency > 0) {
             caqm = g_new(async_dns_queue_msg_t,1);
             caqm->family = AF_INET6;
             memcpy(&caqm->addr.ip6, addr, sizeof(caqm->addr.ip6));
             async_dns_queue_head = g_list_append(async_dns_queue_head, (gpointer) caqm);
-            fill_dummy_ip6(tp);
-            return tp;
-        }
-#elif defined(HAVE_GETADDRINFO)
-        memset(&sin6, 0, sizeof(sin6));
-        sin6.sin6_family      = AF_INET6;
-        memcpy(sin6.sin6_addr.s6_addr, addr, sizeof(*addr));
-        if (getnameinfo((struct sockaddr *)&sin6, sizeof(sin6),
-                        tp->name, sizeof(tp->name),
-                        NULL, 0, NI_NAMEREQD) == 0) {
-            return tp;
-        }
-#elif defined(HAVE_GETHOSTBYNAME)
-        /* Quick hack to avoid DNS/YP timeout */
-        hostp = gethostbyaddr((const char *)addr, sizeof(*addr), AF_INET6);
-
-        if (hostp != NULL && hostp->h_name[0] != '\0') {
-            g_strlcpy(tp->name, hostp->h_name, MAXNAMELEN);
-            return tp;
         }
 #endif
     }
 
-    /* unknown host or DNS timeout */
-    fill_dummy_ip6(tp);
     return tp;
 
 } /* host_lookup6 */
@@ -2461,6 +2390,7 @@ addr_resolve_pref_init(module_t *nameres)
             "Whether address/name pairs found in captured DNS packets should be used by Wireshark for name resolution.",
             &gbl_resolv_flags.dns_pkt_addr_resolution);
 
+#ifdef HAVE_C_ARES
     prefs_register_bool_preference(nameres, "use_external_name_resolver",
             "Use an external network name resolver",
             "Use your system's configured name resolver"
@@ -2469,13 +2399,7 @@ addr_resolve_pref_init(module_t *nameres)
             " is enabled.",
             &gbl_resolv_flags.use_external_net_name_resolver);
 
-#ifdef HAVE_C_ARES
-    prefs_register_bool_preference(nameres, "concurrent_dns",
-            "Enable concurrent DNS name resolution",
-            "Enable concurrent DNS name resolution. Only"
-            " applies when network name resolution is"
-            " enabled. You probably want to enable this.",
-            &gbl_resolv_flags.concurrent_dns);
+    prefs_register_obsolete_preference(nameres, "concurrent_dns");
 
     prefs_register_uint_preference(nameres, "name_resolve_concurrency",
             "Maximum concurrent requests",
@@ -2486,9 +2410,9 @@ addr_resolve_pref_init(module_t *nameres)
             10,
             &name_resolve_concurrency);
 #else
-    prefs_register_static_text_preference(nameres, "concurrent_dns",
-            "Enable concurrent DNS name resolution: N/A",
-            "Support for concurrent DNS name resolution was not"
+    prefs_register_static_text_preference(nameres, "use_external_name_resolver",
+            "Use an external network name resolver: N/A",
+            "Support for using a concurrent external name resolver was not"
             " compiled into this version of Wireshark");
 #endif
 
@@ -2514,7 +2438,6 @@ disable_name_resolution(void) {
     gbl_resolv_flags.mac_name                           = FALSE;
     gbl_resolv_flags.network_name                       = FALSE;
     gbl_resolv_flags.transport_name                     = FALSE;
-    gbl_resolv_flags.concurrent_dns                     = FALSE;
     gbl_resolv_flags.dns_pkt_addr_resolution            = FALSE;
     gbl_resolv_flags.use_external_net_name_resolver     = FALSE;
     gbl_resolv_flags.vlan_name                          = FALSE;
@@ -2758,17 +2681,15 @@ host_name_lookup_init(void)
     }
     g_free(hostspath);
 #ifdef HAVE_C_ARES
-    if (gbl_resolv_flags.concurrent_dns) {
 #ifdef CARES_HAVE_ARES_LIBRARY_INIT
-        if (ares_library_init(ARES_LIB_INIT_ALL) == ARES_SUCCESS) {
+    if (ares_library_init(ARES_LIB_INIT_ALL) == ARES_SUCCESS) {
 #endif
-            if (ares_init(&ghba_chan) == ARES_SUCCESS && ares_init(&ghbn_chan) == ARES_SUCCESS) {
-                async_dns_initialized = TRUE;
-            }
-#ifdef CARES_HAVE_ARES_LIBRARY_INIT
+        if (ares_init(&ghba_chan) == ARES_SUCCESS && ares_init(&ghbn_chan) == ARES_SUCCESS) {
+            async_dns_initialized = TRUE;
         }
-#endif
+#ifdef CARES_HAVE_ARES_LIBRARY_INIT
     }
+#endif
 #else
 #endif /* HAVE_C_ARES */
 
@@ -3195,10 +3116,6 @@ get_host_ipaddr(const char *host, guint32 *addrp)
     int nfds;
     fd_set rfds, wfds;
     async_hostent_t ahe;
-#elif defined(HAVE_GETADDRINFO)
-    struct addrinfo hint, *result = NULL;
-#elif defined(HAVE_GETHOSTBYNAME)
-    struct hostent *hp;
 #endif
 
     /*
@@ -3221,9 +3138,7 @@ get_host_ipaddr(const char *host, guint32 *addrp)
         }
 
 #ifdef HAVE_C_ARES
-        if (! (gbl_resolv_flags.concurrent_dns) ||
-                name_resolve_concurrency < 1 ||
-                ! async_dns_initialized) {
+        if (!async_dns_initialized || name_resolve_concurrency < 1) {
             return FALSE;
         }
         ahe.addr_size = (int) sizeof (struct in_addr);
@@ -3246,37 +3161,6 @@ get_host_ipaddr(const char *host, guint32 *addrp)
             return TRUE;
         }
         return FALSE;
-#elif defined(HAVE_GETADDRINFO)
-        /*
-         * This can be slow, particularly for capture files with lots of
-         * addresses. Should we just return FALSE instead?
-         */
-        memset(&hint, 0, sizeof(hint));
-        hint.ai_family = AF_INET;
-        if (getaddrinfo(host, NULL, &hint, &result) == 0) {
-            /* Probably more checks than necessary */
-            if (result != NULL) {
-                gboolean ret_val = FALSE;
-                if (result->ai_family == AF_INET && result->ai_addrlen == 4) {
-                    memcpy(&ipaddr, result->ai_addr->sa_data, result->ai_addrlen);
-                    ret_val = TRUE;
-                }
-                freeaddrinfo(result);
-                return ret_val;
-            }
-        }
-#elif defined(HAVE_GETHOSTBYNAME)
-        hp = gethostbyname(host);
-        if (hp == NULL) {
-            /* No. */
-            return FALSE;
-            /* Apparently, some versions of gethostbyaddr can
-             * return IPv6 addresses. */
-         } else if (hp->h_length <= (int) sizeof (struct in_addr)) {
-             memcpy(&ipaddr, hp->h_addr, hp->h_length);
-         } else {
-             return FALSE;
-         }
 #endif
     } else {
         /* Does the string really contain dotted-quad IP?
@@ -3306,10 +3190,6 @@ get_host_ipaddr6(const char *host, struct e_in6_addr *addrp)
     int nfds;
     fd_set rfds, wfds;
     async_hostent_t ahe;
-#elif defined(HAVE_GETADDRINFO)
-    struct addrinfo hint, *result = NULL;
-#elif defined(HAVE_GETHOSTBYNAME2)
-    struct hostent *hp;
 #endif /* HAVE_C_ARES */
 
     if (str_to_ip6(host, addrp))
@@ -3329,9 +3209,7 @@ get_host_ipaddr6(const char *host, struct e_in6_addr *addrp)
 
     /* try FQDN */
 #ifdef HAVE_C_ARES
-    if (! (gbl_resolv_flags.concurrent_dns) ||
-            name_resolve_concurrency < 1 ||
-            ! async_dns_initialized) {
+    if (!async_dns_initialized || name_resolve_concurrency < 1) {
         return FALSE;
     }
     ahe.addr_size = (int) sizeof (struct e_in6_addr);
@@ -3353,31 +3231,6 @@ get_host_ipaddr6(const char *host, struct e_in6_addr *addrp)
     if (ahe.addr_size == ahe.copied) {
         return TRUE;
     }
-#elif defined(HAVE_GETADDRINFO)
-    /*
-     * This can be slow, particularly for capture files with lots of
-     * addresses. Should we just return FALSE instead?
-     */
-    memset(&hint, 0, sizeof(hint));
-    hint.ai_family = AF_INET6;
-    if (getaddrinfo(host, NULL, &hint, &result) == 0) {
-        /* Probably more checks than necessary */
-        if (result != NULL) {
-            gboolean ret_val = FALSE;
-            if (result->ai_family == AF_INET6 && result->ai_addrlen == sizeof(struct e_in6_addr)) {
-                memcpy(addrp, result->ai_addr->sa_data, result->ai_addrlen);
-                ret_val = TRUE;
-            }
-            freeaddrinfo(result);
-            return ret_val;
-        }
-    }
-#elif defined(HAVE_GETHOSTBYNAME2)
-    hp = gethostbyname2(host, AF_INET6);
-    if (hp != NULL && hp->h_length == sizeof(struct e_in6_addr)) {
-        memcpy(addrp, hp->h_addr, hp->h_length);
-        return TRUE;
-    }
 #endif
 
     return FALSE;
@@ -3389,13 +3242,14 @@ get_host_ipaddr6(const char *host, struct e_in6_addr *addrp)
  * that we don't know)
  */
 const char *
-host_ip_af(const char *host
-#if !defined(HAVE_GETADDRINFO) || !defined(HAVE_GETHOSTBYNAME2)
-        _U_
+#ifdef HAVE_GETADDRINFO
+host_ip_af(const char *host)
+#else
+host_ip_af(const char *host _U_)
 #endif
-        )
 {
     const char *af = "ip";
+
 #ifdef HAVE_GETADDRINFO
     struct addrinfo hint, *result = NULL;
     memset(&hint, 0, sizeof(hint));
@@ -3406,9 +3260,6 @@ host_ip_af(const char *host
         }
         freeaddrinfo(result);
     }
-#elif defined(HAVE_GETHOSTBYNAME2)
-    struct hostent *h;
-    return (h = gethostbyname2(host, AF_INET6)) && h->h_addrtype == AF_INET6 ? "ip6" : "ip";
 #endif
     return af;
 }
diff --git a/epan/addr_resolv.h b/epan/addr_resolv.h
index e1b49cdce8..678dd8d9d5 100644
--- a/epan/addr_resolv.h
+++ b/epan/addr_resolv.h
@@ -58,7 +58,6 @@ typedef struct _e_addr_resolve {
   gboolean mac_name;                          /**< Whether to resolve Ethernet MAC to manufacturer names */
   gboolean network_name;                      /**< Whether to resolve IPv4, IPv6, and IPX addresses into host names */
   gboolean transport_name;                    /**< Whether to resolve TCP/UDP/DCCP/SCTP ports into service names */
-  gboolean concurrent_dns;                    /**< Whether to use concurrent DNS name resolution */
   gboolean dns_pkt_addr_resolution;           /**< Whether to resolve addresses using captured DNS packets */
   gboolean use_external_net_name_resolver;    /**< Whether to system's configured DNS server to resolve names */
   gboolean load_hosts_file_from_profile_only; /**< Whether to only load the hosts in the current profile, not hosts files */
diff --git a/epan/ipproto.c b/epan/ipproto.c
index 4b1814ea88..f328bf504a 100644
--- a/epan/ipproto.c
+++ b/epan/ipproto.c
@@ -282,7 +282,7 @@ const char *ipprotostr(const int proto) {
      * protocol names?
      */
     if (gbl_resolv_flags.mac_name || gbl_resolv_flags.network_name ||
-        gbl_resolv_flags.transport_name || gbl_resolv_flags.concurrent_dns) {
+        gbl_resolv_flags.transport_name) {
         static char buf[128];
         struct protoent *pe;
 
diff --git a/epan/prefs.c b/epan/prefs.c
index fb99675ba0..c7d7a2b906 100644
--- a/epan/prefs.c
+++ b/epan/prefs.c
@@ -3909,7 +3909,8 @@ string_to_name_resolve(const char *string, e_addr_resolve *name_resolve)
             name_resolve->transport_name = TRUE;
             break;
         case 'C':
-            name_resolve->concurrent_dns = TRUE;
+            /* DEPRECATED */
+            /* name_resolve->concurrent_dns */
             break;
         case 'd':
             name_resolve->dns_pkt_addr_resolution = TRUE;
@@ -4067,7 +4068,6 @@ set_pref(gchar *pref_name, const gchar *value, void *private_data _U_,
             gbl_resolv_flags.mac_name = TRUE;
             gbl_resolv_flags.network_name = TRUE;
             gbl_resolv_flags.transport_name = TRUE;
-            gbl_resolv_flags.concurrent_dns = TRUE;
         }
         else if (g_ascii_strcasecmp(value, "false") == 0) {
             disable_name_resolution();
diff --git a/rawshark.c b/rawshark.c
index 8fe77133cf..df5a622e3b 100644
--- a/rawshark.c
+++ b/rawshark.c
@@ -189,7 +189,7 @@ print_usage(FILE *output)
     fprintf(output, "                           packet encapsulation or protocol\n");
     fprintf(output, "  -F <field>               field to display\n");
     fprintf(output, "  -n                       disable all name resolution (def: all enabled)\n");
-    fprintf(output, "  -N <name resolve flags>  enable specific name resolution(s): \"mnNtCd\"\n");
+    fprintf(output, "  -N <name resolve flags>  enable specific name resolution(s): \"mnNtd\"\n");
     fprintf(output, "  -p                       use the system's packet header format\n");
     fprintf(output, "                           (which may have 64-bit timestamps)\n");
     fprintf(output, "  -R <read filter>         packet filter in Wireshark display filter syntax\n");
@@ -629,7 +629,7 @@ main(int argc, char *argv[])
             case 'N':        /* Select what types of addresses/port #s to resolve */
                 badopt = string_to_name_resolve(optarg, &gbl_resolv_flags);
                 if (badopt != '\0') {
-                    cmdarg_err("-N specifies unknown resolving option '%c'; valid options are 'C', 'd', m', 'n', 'N', and 't'",
+                    cmdarg_err("-N specifies unknown resolving option '%c'; valid options are 'd', m', 'n', 'N', and 't'",
                                badopt);
                     exit(1);
                 }
diff --git a/tshark.c b/tshark.c
index 7407e82ea8..3a2949390d 100644
--- a/tshark.c
+++ b/tshark.c
@@ -1531,8 +1531,7 @@ main(int argc, char *argv[])
       if (badopt != '\0') {
         cmdarg_err("-N specifies unknown resolving option '%c'; valid options are:",
                    badopt);
-        cmdarg_err_cont("\t'C' to enable concurrent (asynchronous) DNS lookups\n"
-                        "\t'd' to enable address resolution from captured DNS packets\n"
+        cmdarg_err_cont("\t'd' to enable address resolution from captured DNS packets\n"
                         "\t'm' to enable MAC address resolution\n"
                         "\t'n' to enable network address resolution\n"
                         "\t'N' to enable using external resolvers (e.g., DNS)\n"
@@ -2984,7 +2983,7 @@ process_packet_first_pass(capture_file *cf, epan_dissect_t *edt,
      do a dissection and do so. */
   if (edt) {
     if (gbl_resolv_flags.mac_name || gbl_resolv_flags.network_name ||
-        gbl_resolv_flags.transport_name || gbl_resolv_flags.concurrent_dns)
+        gbl_resolv_flags.transport_name)
       /* Grab any resolved addresses */
       host_name_lookup_process();
 
@@ -3057,7 +3056,7 @@ process_packet_second_pass(capture_file *cf, epan_dissect_t *edt, frame_data *fd
      do a dissection and do so. */
   if (edt) {
     if (gbl_resolv_flags.mac_name || gbl_resolv_flags.network_name ||
-        gbl_resolv_flags.transport_name || gbl_resolv_flags.concurrent_dns)
+        gbl_resolv_flags.transport_name)
       /* Grab any resolved addresses */
       host_name_lookup_process();
 
@@ -3696,7 +3695,7 @@ process_packet(capture_file *cf, epan_dissect_t *edt, gint64 offset, struct wtap
      do a dissection and do so. */
   if (edt) {
     if (print_packet_info && (gbl_resolv_flags.mac_name || gbl_resolv_flags.network_name ||
-        gbl_resolv_flags.transport_name || gbl_resolv_flags.concurrent_dns))
+        gbl_resolv_flags.transport_name))
       /* Grab any resolved addresses */
       host_name_lookup_process();
 
diff --git a/ui/gtk/main.c b/ui/gtk/main.c
index efd56f7748..15f713ccb1 100644
--- a/ui/gtk/main.c
+++ b/ui/gtk/main.c
@@ -929,7 +929,6 @@ void resolve_name_cb(GtkWidget *widget _U_, gpointer data _U_)
         TRUE,   /* mac_name */
         TRUE,   /* network_name */
         TRUE,   /* transport_name */
-        TRUE,   /* concurrent_dns */
         TRUE,   /* dns_pkt_addr_resolution */
         TRUE,   /* use_external_net_name_resolver */
         FALSE,  /* load_hosts_file_from_profile_only */
@@ -1213,7 +1212,7 @@ print_usage(gboolean for_help_option) {
     fprintf(output, "Processing:\n");
     fprintf(output, "  -R <read filter>         packet filter in Wireshark display filter syntax\n");
     fprintf(output, "  -n                       disable all name resolutions (def: all enabled)\n");
-    fprintf(output, "  -N <name resolve flags>  enable specific name resolution(s): \"mnNtCd\"\n");
+    fprintf(output, "  -N <name resolve flags>  enable specific name resolution(s): \"mnNtd\"\n");
     fprintf(output, "  --disable-protocol <proto_name>\n");
     fprintf(output, "                           disable dissection of proto_name\n");
     fprintf(output, "  --enable-heuristic <short_name>\n");
@@ -2712,7 +2711,7 @@ main(int argc, char *argv[])
             case 'N':        /* Select what types of addresses/port #s to resolve */
                 badopt = string_to_name_resolve(optarg, &gbl_resolv_flags);
                 if (badopt != '\0') {
-                    cmdarg_err("-N specifies unknown resolving option '%c'; valid options are 'C', 'd', m', 'n', 'N', and 't'",
+                    cmdarg_err("-N specifies unknown resolving option '%c'; valid options are 'd', m', 'n', 'N', and 't'",
                                badopt);
                     exit(1);
                 }
diff --git a/ui/gtk/main_menubar.c b/ui/gtk/main_menubar.c
index bcd9024806..751b7db862 100644
--- a/ui/gtk/main_menubar.c
+++ b/ui/gtk/main_menubar.c
@@ -4703,7 +4703,7 @@ set_menus_for_selected_packet(capture_file *cf)
                          frame_selected);
     set_menu_sensitivity(ui_manager_tree_view_menu, "/TreeViewPopup/ResolveName",
                          frame_selected && (gbl_resolv_flags.mac_name || gbl_resolv_flags.network_name ||
-                                            gbl_resolv_flags.transport_name || gbl_resolv_flags.concurrent_dns));
+                                            gbl_resolv_flags.transport_name));
     set_menu_sensitivity(ui_manager_main_menubar, "/Menubar/AnalyzeMenu/FollowTCPStream",
                          is_tcp);
     set_menu_sensitivity(ui_manager_main_menubar, "/Menubar/AnalyzeMenu/FollowUDPStream",
@@ -4716,7 +4716,7 @@ set_menus_for_selected_packet(capture_file *cf)
                          frame_selected && decode_as_ok());
     set_menu_sensitivity(ui_manager_main_menubar, "/Menubar/ViewMenu/NameResolution/ResolveName",
                          frame_selected && (gbl_resolv_flags.mac_name || gbl_resolv_flags.network_name ||
-                                            gbl_resolv_flags.transport_name || gbl_resolv_flags.concurrent_dns));
+                                            gbl_resolv_flags.transport_name));
     set_menu_sensitivity(ui_manager_main_menubar, "/Menubar/ToolsMenu/FirewallACLRules",
                          frame_selected);
     set_menu_sensitivity(ui_manager_main_menubar, "/Menubar/StatisticsMenu/TCPStreamGraphMenu",
diff --git a/ui/qt/main_window_slots.cpp b/ui/qt/main_window_slots.cpp
index f543890d04..33ffcd4169 100644
--- a/ui/qt/main_window_slots.cpp
+++ b/ui/qt/main_window_slots.cpp
@@ -1169,7 +1169,7 @@ void MainWindow::setMenusForSelectedPacket()
 
 //    set_menu_sensitivity(ui_manager_main_menubar, "/Menubar/ViewMenu/NameResolution/ResolveName",
 //                         frame_selected && (gbl_resolv_flags.mac_name || gbl_resolv_flags.network_name ||
-//                                            gbl_resolv_flags.transport_name || gbl_resolv_flags.concurrent_dns));
+//                                            gbl_resolv_flags.transport_name));
 //    set_menu_sensitivity(ui_manager_main_menubar, "/Menubar/ToolsMenu/FirewallACLRules",
 //                         frame_selected);
     main_ui_->menuTcpStreamGraphs->setEnabled(is_tcp);
@@ -1266,7 +1266,7 @@ void MainWindow::setMenusForSelectedTreeRow(field_info *fi) {
 
 //    set_menu_sensitivity(ui_manager_tree_view_menu, "/TreeViewPopup/ResolveName",
 //                         frame_selected && (gbl_resolv_flags.mac_name || gbl_resolv_flags.network_name ||
-//                                            gbl_resolv_flags.transport_name || gbl_resolv_flags.concurrent_dns));
+//                                            gbl_resolv_flags.transport_name));
 
     main_ui_->actionAnalyzeAAFSelected->setEnabled(can_match_selected);
     main_ui_->actionAnalyzeAAFNotSelected->setEnabled(can_match_selected);
diff --git a/wireshark-qt.cpp b/wireshark-qt.cpp
index 5c474a69bc..7ba61381e7 100644
--- a/wireshark-qt.cpp
+++ b/wireshark-qt.cpp
@@ -215,7 +215,7 @@ print_usage(gboolean for_help_option) {
     fprintf(output, "Processing:\n");
     fprintf(output, "  -R <read filter>         packet filter in Wireshark display filter syntax\n");
     fprintf(output, "  -n                       disable all name resolutions (def: all enabled)\n");
-    fprintf(output, "  -N <name resolve flags>  enable specific name resolution(s): \"mnNtCd\"\n");
+    fprintf(output, "  -N <name resolve flags>  enable specific name resolution(s): \"mnNtd\"\n");
     fprintf(output, "  --disable-protocol <proto_name>\n");
     fprintf(output, "                           disable dissection of proto_name\n");
     fprintf(output, "  --enable-heuristic <short_name>\n");
@@ -948,7 +948,7 @@ int main(int argc, char *argv[])
         case 'N':        /* Select what types of addresses/port #s to resolve */
             badopt = string_to_name_resolve(optarg, &gbl_resolv_flags);
             if (badopt != '\0') {
-                cmdarg_err("-N specifies unknown resolving option '%c'; valid options are 'C', 'd', m', 'n', 'N', and 't'",
+                cmdarg_err("-N specifies unknown resolving option '%c'; valid options are 'd', m', 'n', 'N', and 't'",
                            badopt);
                 exit(1);
             }