add prepend communities

natesales · Dec 8, 2020 · 0ba36dc · 0ba36dc
1 parent 0b000e6
commit 0ba36dc
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Showing 3 changed files with 25 additions and 19 deletions.
diff --git a/README.md b/README.md
@@ -96,7 +96,10 @@ bcg strips private ASNs before exporting to upstream sessions in range `[64512..
 | ASN,0,101 | Learned from upstream     |
 | ASN,0,102 | Learned from peer         |
 | ASN,0,103 | Learned from downstream   |
-| ASN,0,200 | Don't export to upstreams |
+| ASN,1,200 | Don't export to upstreams |
+| ASN,1,301 | Prepend once              |
+| ASN,1,302 | Prepend twice             |
+| ASN,1,303 | Prepend three times       |
 
 #### Global Configuration Options
 

diff --git a/templates/global.tmpl b/templates/global.tmpl
@@ -207,8 +207,8 @@ function reject_transit_paths() {
   if (bgp_path ~ TRANSIT_ASNS) then _reject("transit path");
 }
 
-function strip_communities() {
-  bgp_large_community.delete([(ASN, *, *)]);
+function strip_info_communities() {
+  bgp_large_community.delete([(ASN, 0, *)]);
 }
 
 function accept_local() {
@@ -228,22 +228,24 @@ function accept_local() {
 }
 
 function process_prepends() {
-  if ((ASN,0,401) ~ bgp_community) then {
-    print "Adding single prepend for ", net;
-    bgp_path.prepend(ASN);
-  }
+  if ((ASN,0,103) ~ bgp_community) then { # Learned from downstream
+    if ((ASN,1,401) ~ bgp_community) then {
+      print "Adding single prepend for ", net;
+      bgp_path.prepend(ASN);
+    }
 
-  if ((ASN,0,402) ~ bgp_community) then {
-    print "Adding double prepend for ", net;
-    bgp_path.prepend(ASN);
-    bgp_path.prepend(ASN);
-  }
+    if ((ASN,1,402) ~ bgp_community) then {
+      print "Adding double prepend for ", net;
+      bgp_path.prepend(ASN);
+      bgp_path.prepend(ASN);
+    }
 
-  if ((ASN,0,403) ~ bgp_community) then {
-    print "Adding triple prepend for ", net;
-    bgp_path.prepend(ASN);
-    bgp_path.prepend(ASN);
-    bgp_path.prepend(ASN);
+    if ((ASN,1,403) ~ bgp_community) then {
+      print "Adding triple prepend for ", net;
+      bgp_path.prepend(ASN);
+      bgp_path.prepend(ASN);
+      bgp_path.prepend(ASN);
+    }
   }
 }
 

diff --git a/templates/peer.tmpl b/templates/peer.tmpl
@@ -43,7 +43,7 @@ protocol bgp {{ $peer.Name }}v{{ $af }}_{{ $i }} {
         {{ if eq $peer.Asn $global.Asn }}next hop self;{{ end }}
         import filter {
             {{ if not $peer.SkipFilter }}reject_bogons();{{ end }}
-            strip_communities();
+            strip_info_communities();
             bgp_local_pref = {{ $peer.LocalPref }};
             honor_graceful_shutdown();
             {{ $peer.PreImport }}
@@ -80,9 +80,10 @@ protocol bgp {{ $peer.Name }}v{{ $af }}_{{ $i }} {
             {{ $peer.PreExport }}
             {{ if or $global.OriginSet4 $global.OriginSet6 -}}
             accept_local(); # Originated
+            process_prepends();
             {{ end -}}
             {{ if eq $peer.Type "upstream" -}}
-            if ((ASN,0,200) ~ bgp_large_community) then reject; # Don't export to upstreams
+            if ((ASN,1,200) ~ bgp_large_community) then reject; # Don't export to upstreams
             if ((ASN,0,103) ~ bgp_large_community) then accept; # Downstream
             {{ else if or (eq $peer.Type "peer") (eq $peer.Type "import-valid") -}}
             if ((ASN,0,103) ~ bgp_large_community) then accept; # Downstream