BGP_example_2.md

+# BGP example 2
+
+Here is an example of a gateway router for a leaf AS with several upstreams (multihoming). This config is an extension of [BGP example 1](BGP_example_1). We cannot use the default route locally, we import routes from BGP and use BGP to choose between upstreams for each prefix - some networks are closer using bgp_abc, other using bgp_def. But we don't want all these routes received from BGP (cca 300k routes) export to the OSPF. Therefore, we propagate the default route (from static_ospf protocol) to the OSPF protocol (it does not matter that the default route is an unreachable route, other OSPF routers that receive it will compute _via_ according to the shortest path to this gateway).
+
+This config should be extended to contain proper import filters for bgp protocols to prevent upstreams to send us some bogus routes. For details see the [BGP filtering](BGP_filtering) for more examples.
+
+    log syslog all;
+    
+    router id A.B.C.D;
+    
+    protocol device {
+            scan time 10;
+    }
+    
+    protocol kernel {
+            export all;
+            scan time 15;
+    }
+    
+    protocol static static_bgp { 
+            import all;
+    
+            route A.B.C.0/24 reject;
+            route D.E.F.0/24 reject;
+    }
+    
+    protocol static static_ospf {
+            import all;
+    
+            route 0.0.0.0/0 reject;
+    }
+    
+    protocol bgp bgp_abc {
+            import all;
+            export where proto = "static_bgp";
+    
+            local as XXXX;
+            neighbor W1.X1.Y1.Z1 as YYYY;
+    }
+    
+    protocol bgp bgp_def {
+            import all;
+            export where proto = "static_bgp";
+    
+            local as XXXX;
+            neighbor W2.X2.Y2.Z2 as ZZZZ;
+    }
+    
+    protocol ospf {
+            import all;
+            export where proto = "static_ospf";
+    
+            ...
+    }