diff --git a/lib/App/Netdisco/Transport/SNMP.pm b/lib/App/Netdisco/Transport/SNMP.pm
index 04f3b1a4..fa397c08 100644
--- a/lib/App/Netdisco/Transport/SNMP.pm
+++ b/lib/App/Netdisco/Transport/SNMP.pm
@@ -1,6 +1,8 @@
 package App::Netdisco::Transport::SNMP;
 
 use Dancer qw/:syntax :script/;
+use Dancer::Plugin::DBIC 'schema';
+
 use App::Netdisco::Util::SNMP 'get_communities';
 use App::Netdisco::Util::Device 'get_device';
 use App::Netdisco::Util::Permission ':all';
@@ -9,6 +11,7 @@ use SNMP::Info;
 use Try::Tiny;
 use Module::Load ();
 use Path::Class 'dir';
+use NetAddr::IP::Lite ':lower';
 
 use base 'Dancer::Object::Singleton';
 
@@ -61,6 +64,34 @@ sub reader_for {
     = _snmp_connect_generic('read', $device, $useclass));
 }
 
+=head1 test_connection( $ip )
+
+Similar to C<reader_for> but will use the literal IP address passed, and does
+not support specifying the device class. The purpose is to test the SNMP
+connectivity to the device before a renumber.
+
+Attempts to have no side effect, however there will be a stored SNMP
+authentication hint (tag) in the database if the connection is successful.
+
+Returns C<undef> if the connection fails.
+
+=cut
+
+sub test_connection {
+  my ($class, $ip) = @_;
+  my $addr = NetAddr::IP::Lite->new($ip) or return undef;
+  # avoid renumbering to localhost loopbacks
+  return undef if $addr->addr eq '0.0.0.0'
+                  or check_acl_no($addr->addr, 'group:__LOCAL_ADDRESSES__');
+  my $device = schema('netdisco')->resultset('Device')
+    ->new_result({ ip => $addr->addr }) or return undef;
+  my $readers = $class->instance->readers or return undef;
+  return $readers->{$device->ip} if exists $readers->{$device->ip};
+  debug sprintf 'snmp reader cache warm: [%s]', $device->ip;
+  return ($readers->{$device->ip}
+    = _snmp_connect_generic('read', $device, $useclass));
+}
+
 =head1 writer_for( $ip, $useclass? )
 
 Same as C<reader_for> but uses the read-write community strings from the
diff --git a/lib/App/Netdisco/Util/SNMP.pm b/lib/App/Netdisco/Util/SNMP.pm
index 832cd958..f75dcf73 100644
--- a/lib/App/Netdisco/Util/SNMP.pm
+++ b/lib/App/Netdisco/Util/SNMP.pm
@@ -1,6 +1,7 @@
 package App::Netdisco::Util::SNMP;
 
 use Dancer qw/:syntax :script/;
+use App::Netdisco::Util::DNS 'hostname_from_ip';
 use App::Netdisco::Util::Permission ':all';
 
 use base 'Exporter';
@@ -138,7 +139,8 @@ sub get_communities {
 
   # clean the community table of obsolete tags
   eval { $device->community->update({$tag_name => undef}) }
-    if not $stored_tag or !exists $seen_tags->{ $stored_tag };
+    if $device->in_storage
+       and (not $stored_tag or !exists $seen_tags->{ $stored_tag });
 
   return ( @communities, @$config );
 }
@@ -147,7 +149,7 @@ sub _get_external_community {
   my ($device, $mode) = @_;
   my $cmd = setting('get_community');
   my $ip = $device->ip;
-  my $host = $device->dns || $ip;
+  my $host = ($device->dns || hostname_from_ip($ip) || $ip);
 
   if (defined $cmd and length $cmd) {
       # replace variables
diff --git a/lib/App/Netdisco/Worker/Plugin/Discover/CanonicalIP.pm b/lib/App/Netdisco/Worker/Plugin/Discover/CanonicalIP.pm
index f6b86d71..105f4185 100644
--- a/lib/App/Netdisco/Worker/Plugin/Discover/CanonicalIP.pm
+++ b/lib/App/Netdisco/Worker/Plugin/Discover/CanonicalIP.pm
@@ -22,7 +22,7 @@ register_worker({ phase => 'main', driver => 'snmp' }, sub {
   my $revofname = ipv4_from_hostname($snmp->name);
 
   if (setting('reverse_sysname') and $revofname) {
-    if ($snmp->snmp_connect_ip( $new_ip )) {
+    if (App::Netdisco::Transport::SNMP->test_connection( $new_ip )) {
       $new_ip = $revofname;
     }
     else {
@@ -46,8 +46,7 @@ register_worker({ phase => 'main', driver => 'snmp' }, sub {
           if (check_acl_only($device, $key)
                 and check_acl_only($alias, $map->{$key})) {
 
-            # if ($snmp->snmp_connect_ip( $alias->alias )) { FIXME
-            if (App::Netdisco::Transport::SNMP->reader_for( $alias->alias )) {
+            if (App::Netdisco::Transport::SNMP->test_connection( $alias->alias )) {
               $new_ip = $alias->alias;
               last ALIAS;
             }