Index: openacs-4/packages/acs-tcl/tcl/00-icanuse-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-tcl/tcl/00-icanuse-procs.tcl,v
diff -u -r1.1.2.23 -r1.1.2.24
--- openacs-4/packages/acs-tcl/tcl/00-icanuse-procs.tcl	14 Jan 2021 21:35:43 -0000	1.1.2.23
+++ openacs-4/packages/acs-tcl/tcl/00-icanuse-procs.tcl	17 Feb 2021 20:51:42 -0000	1.1.2.24
@@ -110,11 +110,14 @@
 ::acs::register_icanuse "ns_writer"                 {[info commands ::ns_writer] ne ""}
 ::acs::register_icanuse "nsv_dict"                  [acs::cmd_error_contains {nsv_dict get ""} -varname]
 
-# The feature NaviServer to return a dict as result of "ns_http run"
-# came at the same time, when "ns_http stats" was introduced.
+#
+# The following commands check indirectly the availability, since the
+# commands require connections etc.  These features were introduced
+# after the queried functionality was introduced.
+#
 ::acs::register_icanuse "ns_http results dict"      [acs::cmd_has_subcommand ns_http stats]
+::acs::register_icanuse "ns_conn peeraddr -source"  [acs::cmd_has_subcommand ns_connchan status]
 
-
 #
 # Add some compatibility procs for AOLserver or older NaviServer versions
 #
Index: openacs-4/packages/acs-tcl/tcl/request-processor-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-tcl/tcl/request-processor-procs.tcl,v
diff -u -r1.153.2.30 -r1.153.2.31
--- openacs-4/packages/acs-tcl/tcl/request-processor-procs.tcl	1 Feb 2021 10:51:09 -0000	1.153.2.30
+++ openacs-4/packages/acs-tcl/tcl/request-processor-procs.tcl	17 Feb 2021 20:51:42 -0000	1.153.2.31
@@ -1636,18 +1636,26 @@
                             return 0
                         }
                         peeraddr {
-                            if {[ns_config "ns/parameters" ReverseProxyMode false]} {
+                            #
+                            # Newer versions of NaviServer (4.99.20)
+                            # handle already ReverseProxyMode
+                            # internally.
+                            #
+                            if {![acs::icanuse "ns_conn peeraddr -source"]
+                                && [ns_config "ns/parameters" ReverseProxyMode false]
+                            } {
+                                #
                                 # Try to get the address provided by a
                                 # reverse proxy such as NGINX via
-                                # X-Forwarded-For, if available
+                                # X-Forwarded-For, if available.
+                                #
                                 set headers [ns_conn headers]
                                 set i [ns_set ifind $headers "X-Forwarded-For"]
                                 if {$i > -1 } {
                                     return [ns_set value $headers $i]
                                 }
                             }
-                            # return the physical peer address
-                            return [ns_conn $var]
+                            return [set ad_conn(peeraddr) [ns_conn peeraddr]]
                         }
 
                         mobile_p {