add NGX_ENETDOWN, NGX_ENETUNREACH, and NGX_EHOSTDOWN

src/core/ngx_connection.c

diff --git a/src/core/ngx_connection.c b/src/core/ngx_connection.c
index e0a6ba2..b31daaa 100644
--- a/src/core/ngx_connection.c
+++ b/src/core/ngx_connection.c
@@ -767,6 +767,9 @@
         || err == NGX_ENOTCONN
         || err == NGX_ETIMEDOUT
         || err == NGX_ECONNREFUSED
+        || err == NGX_ENETDOWN
+        || err == NGX_ENETUNREACH
+        || err == NGX_EHOSTDOWN
         || err == NGX_EHOSTUNREACH)
     {
         switch (c->log_error) {

src/event/ngx_event_connect.c

diff --git a/src/event/ngx_event_connect.c b/src/event/ngx_event_connect.c
index d8bd7f4..5ae7b23 100644
--- a/src/event/ngx_event_connect.c
+++ b/src/event/ngx_event_connect.c
@@ -143,8 +143,14 @@
 
         if (err != NGX_EINPROGRESS && err != NGX_EAGAIN) {
 
-            if (err == NGX_ECONNREFUSED || err == NGX_EHOSTUNREACH) {
+            if (err == NGX_ECONNREFUSED
+                || err == NGX_ENETDOWN
+                || err == NGX_ENETUNREACH
+                || err == NGX_EHOSTDOWN
+                || err == NGX_EHOSTUNREACH)
+            {
                 level = NGX_LOG_ERR;
+
             } else {
                 level = NGX_LOG_CRIT;
             }

src/event/ngx_event_openssl.c

diff --git a/src/event/ngx_event_openssl.c b/src/event/ngx_event_openssl.c
index 6de7742..edbb16f 100644
--- a/src/event/ngx_event_openssl.c
+++ b/src/event/ngx_event_openssl.c
@@ -1121,6 +1121,9 @@
             || err == NGX_ETIMEDOUT
 #endif
             || err == NGX_ECONNREFUSED
+            || err == NGX_ENETDOWN
+            || err == NGX_ENETUNREACH
+            || err == NGX_EHOSTDOWN
             || err == NGX_EHOSTUNREACH)
         {
             switch (c->log_error) {

src/os/unix/ngx_errno.h

diff --git a/src/os/unix/ngx_errno.h b/src/os/unix/ngx_errno.h
index b941a43..c50d787 100644
--- a/src/os/unix/ngx_errno.h
+++ b/src/os/unix/ngx_errno.h
@@ -37,6 +37,9 @@
 #define NGX_ETIMEDOUT     ETIMEDOUT
 #define NGX_ECONNREFUSED  ECONNREFUSED
 #define NGX_ENAMETOOLONG  ENAMETOOLONG
+#define NGX_ENETDOWN      ENETDOWN
+#define NGX_ENETUNREACH   ENETUNREACH
+#define NGX_EHOSTDOWN     EHOSTDOWN
 #define NGX_EHOSTUNREACH  EHOSTUNREACH
 #define NGX_ENOSYS        ENOSYS
 #define NGX_ECANCELED     ECANCELED

src/os/win32/ngx_errno.h

diff --git a/src/os/win32/ngx_errno.h b/src/os/win32/ngx_errno.h
index 588d288..52d04bc 100644
--- a/src/os/win32/ngx_errno.h
+++ b/src/os/win32/ngx_errno.h
@@ -40,6 +40,9 @@
 #define NGX_ETIMEDOUT              WSAETIMEDOUT
 #define NGX_ECONNREFUSED           WSAECONNREFUSED
 #define NGX_ENAMETOOLONG           ERROR_BAD_PATHNAME
+#define NGX_ENETDOWN               WSAENETDOWN
+#define NGX_ENETUNREACH            WSAENETUNREACH
+#define NGX_EHOSTDOWN              WSAEHOSTDOWN
 #define NGX_EHOSTUNREACH           WSAEHOSTUNREACH
 #define NGX_ENOMOREFILES           ERROR_NO_MORE_FILES