+<sect>Routing and Filtering
+
+<sect1>Introduction
+
+<P>
+From DXSpider version 1.48, major changes were introduced to the way
+node connections are treated. This is part of an ongoing process to
+remove problems with loops and to enable talk and other functions to
+propagate across the whole of the worldwide cluster network. In fact,
+in a Spider network, it would be useful, perhaps even necessary to
+have loops. This would give real resilience to the network, meaning
+that if a link dropped, the information flow would simply come in and
+go out via a different route. Of course, we do not have a complete
+network of Spider nodes, there are other programs out there. Some of
+these do not have any protection from loops. Certainly AK1A does not
+handle loops well at all. It is therefore necessary to have some form
+of protection for these nodes.
+
+<P>
+In fact DXSpider has had a simple system for some time which is called
+<it>isolation</it>. This is similar to what in other systems such as
+<bf>clx</bf>, is called <it>passive mode</it>. A more detailed explanation
+of <it>isolation</it> is given further below. This system is still available
+and, for simple networks, is probably all that you need.
+
+<P>
+The new functionality introduced in version 1.48 allows filtering the node
+and user protocol frames on a "per interface" basis. We call this
+<it>route filtering</it>. This is used <bf>instead of</bf>
+<it>isolation</it>.
+
+<p>
+What this really means is that you can control more or less completely
+which user and node management PC protocol frames pass to each of your
+partner nodes. You can also limit what comes into your node from your
+partners. It is even possible to control the settings that your partner
+node has for the routing information that it sends to you
+(using the <it>rcmd</it> command).
+
+<sect1>Route Filters
+
+<p>
+Initially when route filters were being tested we generated a
+"default" filter. Unfortunately it quickly became apparent that this
+might suit the UK cluster network but didn't really fit anybody else.
+However using a default filter is an appropriate thing to do. How, is
+explained further on.
+
+<p>
+The first thing that you must do is determine whether you need to use
+route filtering <bf>at all</bf>. If you are a "normal" node with two or
+three partners and you arranged in an "official" non-looping tree type
+network, then <bf>you do not need to do route filtering</bf> and you will
+feel a lot better for not getting involved. If you are successfully using
+<it>isolation</it> then you also probably don't need to use route filtering.
+
+<p>
+To put it simply, you should not mix Isolation and Route Filtering. It
+will work, of sorts, but you will not get the expected results. If you
+are using Isolation sucessfully at the moment, do not get involved in
+Route Filtering unless you have a good supply of aspirin! Once you have
+started down the road of Route Filtering, do not use Isolation either.
+Use one or the other, not both.
+
+<p>
+You will only require this functionality if you are "well-connected". What
+that means is that you are connected to several different parts of (say)
+the EU cluster and, at the same time, also connected to two or three places
+in the US which, in turn are connected back to the EU. This is called a
+"loop" and if you are seriously looped then you need filtering.
+
+<P>
+I should at this stage give a little bit of background on filters. All
+the filters in Spider work in basically the same way. You can either
+accept or reject various options in order to create the filter rules
+you wish to achieve. Some filters are user settable, others can only
+be altered by the sysop. Route filtering can only be done by the sysop.
+
+<P>
+Anyway, without further discouragement, let me start the process
+of explanation.
+
+<sect1>The node_default filter
+
+<P>
+All normal systems should have a default routing filter and it should
+usually be set to send only the normal, unlooped, view of your
+"national" network. Here in the UK that means nodes from the UK and
+Eire, in EU it is more complex as the networks there grew up in a more
+intertwined way.
+
+<p>
+The generic commands are:-