+<sect1>Basic hop control
+
+<P>
+In /spider/data you will find a file called hop_table.pl. This is the file
+that controls your hop count settings. It has a set of default hops on the
+various PC frames and also a set for each node you want to alter the hops for.
+You may be happy with the default settings of course, but this powerful tool
+can help to protect and improve the network. The file will look something
+like this ...
+
+<tscreen><verb>
+#
+# hop table construction
+#
+
+package DXProt;
+
+# default hopcount to use
+$def_hopcount = 5;
+
+# some variable hop counts based on message type
+%hopcount =
+(
+ 11 => 10,
+ 16 => 10,
+ 17 => 10,
+ 19 => 10,
+ 21 => 10,
+);
+
+
+# the per node hop control thingy
+
+
+%nodehops =
+
+ GB7ADX => { 11 => 8,
+ 12 => 8,
+ 16 => 8,
+ 17 => 8,
+ 19 => 8,
+ 21 => 8,
+ },
+
+ GB7UDX => { 11 => 8,
+ 12 => 8,
+ 16 => 8,
+ 17 => 8,
+ 19 => 8,
+ 21 => 8,
+ },
+ GB7BAA => {
+ 11 => 5,
+ 12 => 8,
+ 16 => 8,
+ 17 => 8,
+ 19 => 8,
+ 21 => 8,
+ },
+};
+</verb></tscreen>
+
+<P>
+Each set of hops is contained within a pair of curly braces and contains a
+series of PC frame types. PC11 for example is a DX spot. The figures here
+are not exhaustive but should give you a good idea of how the file works.
+
+<P>
+You can alter this file at any time, including whilst the cluster is running.
+If you alter the file during runtime, the command <em>load/hops</em> will
+bring your changes into effect.
+
+<sect1>Isolating networks
+
+<P>
+It is possible to isolate networks from each other on a "gateway" node using the
+ <em>set/isolate <node_call></em> command.
+
+<P>
+The effect of this is to partition an isolated network completely from another
+node connected to your node. Your node will appear on and otherwise behave
+normally on every network to which you are connected, but data from an isolated
+network will not cross onto any other network or vice versa. However all the
+spot, announce and WWV traffic and personal messages will still be handled
+locally (because you are a real node on all connected networks), that is locally
+connected users will appear on all networks and will be able to access and
+receive information from all networks transparently. All routed messages will
+be sent as normal, so if a user on one network knows that you are a gateway for
+another network, he can still still send a talk/announce etc message via your
+node and it will be routed across.
+
+<P>
+The only limitation currently is that non-private messages cannot be passed down
+isolated links regardless of whether they are generated locally. This will change
+when the bulletin routing facility is added.
+
+<P>
+If you use isolate on a node connection you will continue to receive all
+information from the isolated partner, however you will not pass any information
+back to the isolated node. There are times when you would like to forward only
+spots across a link (maybe during a contest for example). To do this, isolate
+the node in the normal way and put in a filter in the /spider/filter/spots
+directory to override the isolate. This filter can be very simple and consists
+of just one line ....
+
+<tscreen><verb>
+$in = [
+ [ 1, 0, 'd', 0, 3] # The last figure (3) is the hop count
+];
+</verb></tscreen>