Create bird.

docs/configs/bird.

@@ -0,0 +1,59 @@
+Bird configuration
+==================
+
+Neil Alexander has provided his Bird config for those who want to run a CRXN router using enterprise software.
+
+```bird
+filter crxn4 {
+    if source = RTS_STATIC then accept;
+    if net ~ [ 10.0.0.0/8+ ] then accept;
+    reject;
+};
+
+filter crxn6 {
+    if source = RTS_STATIC then accept;
+    if net ~ [ fd8a:6111:3b1a::/48+ ] then accept;
+    reject;
+};
+
+protocol static {
+    ipv4;
+    route 10.4.3.0/24 blackhole;
+}
+
+protocol static {
+    ipv6;
+    route fd8a:6111:3b1a:eeee::/64 blackhole;
+}
+
+protocol babel {
+    randomize router id yes;
+    ipv4 {
+        import filter crxn4;
+        export filter crxn4;
+    };
+    ipv6 {
+        import filter crxn6;
+        export filter crxn6;
+    };
+    interface "crxn*" {
+        type wired;
+    };
+}
+
+protocol device {
+    scan time 60;
+}
+
+protocol direct {
+    ipv4;
+    ipv6;
+}
+
+protocol kernel {
+    ipv4 {
+        export all;
+        import none;
+    };
+}
+```