Added table config, filter config for Bird configuration tutorial

docs/bird_config.md

@@ -1,6 +1,10 @@
 Configuring Bird
 ================
 
+This document aims to provide the configuration file template required
+for CRXN and along with a description of what parameters need to be set
+for your node specifically.
+
 ## Bird 1.6 and 2.0 differences
 
 Bird 1.6's bird6 (which is what we will use) doesn't prefix anything
@@ -42,3 +46,106 @@ ipv6 {
 };
 ```
 
+---
+
+## Configuration
+
+The configuration template is constructed out of the following files:
+
+1. `filters.conf`
+	* Filter functions and the filter itself
+2. `networks.conf` (TODO: Add at a later stage)
+3. `tables.conf`
+	* The table definitions
+
+#### `filters.conf`
+
+This file holds all the required functions for subnet matching and also
+filters that match to the specific prefix aggregates (regional subnets)
+that CRXN uses.
+
+```
+# Given prefix `in` and `check` see whether or not
+# the `in` is withint `check`
+function rangeCheck (prefix inPrefix; prefix rangePrefix)
+int ourNetworkLen;
+ip ourNetworkID;
+ip inPrefixMasked;
+{
+        # Get the length of our range
+        ourNetworkLen=rangePrefix.len;
+
+        # Get out network ID
+        ourNetworkID=rangePrefix.ip;
+
+        # Mask the inPrefix to that length
+        inPrefixMasked=inPrefix.ip.mask(ourNetworkLen);
+
+        # Check if the masks match
+        if(inPrefixMasked = ourNetworkID)
+        then
+                return true;
+        else
+                return false;
+}
+
+# CRXN Route filter based on regions
+filter crxn6
+{
+        # Allowed ranges (CRXN ranges)
+        # European CRXN: fd8a:6111:3b1a::/48
+        # Souther African CRXN: fded:4178:23fe::/48
+        # Indian: fdfa:1685:3d1::/48
+        # Russian: fda1:8885:300d::/48
+        # American: fd68:b488:442c::/48
+        # Freeloader's IPv6: 2a04:5b81:2050::/44
+        if (rangeCheck(net, fd8a:6111:3b1a::/48) = true)
+        then
+                accept;
+
+        if (rangeCheck(net, fded:4178:23fe::/48) = true)
+        then
+                accept;
+
+        if (rangeCheck(net, fdfa:1685:3d1::/48) = true)
+        then
+                accept;
+
+        if (rangeCheck(net, fda1:8885:300d::/48) = true)
+        then
+                accept;
+
+        if (rangeCheck(net, fd68:b488:442c::/48) = true)
+        then
+                accept;
+
+        if (rangeCheck(net, 2a04:5b81:2050::/44) = true)
+        then
+                accept;
+
+
+
+        # No matches, reject
+        reject;
+}
+```
+
+#### `tables.conf`
+
+This file holds all table definitions. There are only two actually.
+The table `crxn` is the one we actually use, `master` is optional
+and is only present because if one uses `bird-lg-go` (the looking glass
+we use) then it, by default, only shows routes in the `master` table.
+It is meant to have the same routes as the `crxn` table.
+
+```
+# CRXN table
+table crxn;
+
+# master table
+
+# This is the default table, I only use this as the looking glass defaults to looking at it
+
+table master;
+```
+