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15 <H2><A NAME="s4">4. Hop control</A></H2>
17 <P>Starting with version 1.13 there is simple hop control available on a per
18 node basis. Also it is possible to isolate a network completely so that you
19 get all the benefits of being on that network, but can't pass on information
20 from it to any other networks you may be connected to (or vice versa).
22 <H2><A NAME="ss4.1">4.1 Basic hop control</A>
25 <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 ...
30 # hop table construction
35 # default hopcount to use
38 # some variable hop counts based on message type
49 # the per node hop control thingy
81 <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.
83 <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.
85 <H2><A NAME="ss4.2">4.2 Isolating networks</A>
88 <P>It is possible to isolate networks from each other on a "gateway" node using the
89 <EM>set/isolate <node_call></EM> command.
91 <P>The effect of this is to partition an isolated network completely from another
92 nodes connected to your node. Your node will appear on and otherwise behave
93 normally on every network to which you are connected, but data from an isolated
94 network will not cross onto any other network or vice versa. However all the
95 spot, announce and WWV traffic and personal messages will still be handled
96 locally (because you are a real node on all connected networks), that is locally
97 connected users will appear on all networks and will be able to access and
98 receive information from all networks transparently. All routed messages will
99 be sent as normal, so if a user on one network knows that you are a gateway for
100 another network, he can still still send a talk/announce etc message via your
101 node and it will be routed across.
103 <P>The only limitation currently is that non-private messages cannot be passed down
104 isolated links regardless of whether they are generated locally. This will change
105 when the bulletin routing facility is added.
107 <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 ....
112 [ 1, 0, 'd', 0, 3] # The last figure (3) is the hop count
117 <P>There is a lot more on filtering in the next section.
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