+<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>
+<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.
+<P>
+<H2><A NAME="ss1.11">1.11 Isolating networks</A>
+</H2>
+
+<P>It is possible to isolate networks from each other on a "gateway" node using the
+<EM>set/isolate <node_call></EM> command.
+<P>
+<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>
+<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>
+<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 ....
+<P>
+<BLOCKQUOTE><CODE>
+<PRE>
+$in = [
+ [ 1, 0, 'd', 0, 3] # The last figure (3) is the hop count
+];
+</PRE>
+</CODE></BLOCKQUOTE>