BGP: Implement BGP roles

Implement BGP roles as described in RFC 9234. It is  a mechanism for
route leak prevention and automatic route filtering based on common BGP
topology relationships. It defines role capability (controlled by 'local
role' option) and OTC route attribute, which is used for automatic route
filtering and leak detection.

Minor changes done by commiter.

1 files changed, 45 insertions, 1 deletions

diff --git a/proto/bgp/packets.c b/proto/bgp/packets.c
index f13625e2..54423a1a 100644
--- a/proto/bgp/packets.c
+++ b/proto/bgp/packets.c
@@ -238,6 +238,7 @@ bgp_prepare_capabilities(struct bgp_conn *conn)
   caps->ext_messages = p->cf->enable_extended_messages;
   caps->route_refresh = p->cf->enable_refresh;
   caps->enhanced_refresh = p->cf->enable_refresh;
+  caps->role = p->cf->local_role;
 
   if (caps->as4_support)
     caps->as4_number = p->public_as;
@@ -350,6 +351,13 @@ bgp_write_capabilities(struct bgp_conn *conn, byte *buf)
     *buf++ = 0;			/* Capability data length */
   }
 
+  if (caps->role != BGP_ROLE_UNDEFINED)
+  {
+    *buf++ = 9;			/* Capability 9: Announce chosen BGP role */
+    *buf++ = 1;			/* Capability data length */
+    *buf++ = caps->role;
+  }
+
   if (caps->gr_aware)
   {
     *buf++ = 64;		/* Capability 64: Support for graceful restart */
@@ -449,11 +457,15 @@ bgp_read_capabilities(struct bgp_conn *conn, byte *pos, int len)
   struct bgp_proto *p = conn->bgp;
   struct bgp_caps *caps;
   struct bgp_af_caps *ac;
+  uint err_subcode = 0;
   int i, cl;
   u32 af;
 
   if (!conn->remote_caps)
+  {
     caps = mb_allocz(p->p.pool, sizeof(struct bgp_caps) + sizeof(struct bgp_af_caps));
+    caps->role = BGP_ROLE_UNDEFINED;
+  }
   else
   {
     caps = conn->remote_caps;
@@ -513,6 +525,21 @@ bgp_read_capabilities(struct bgp_conn *conn, byte *pos, int len)
       caps->ext_messages = 1;
       break;
 
+    case  9: /* BGP role capability, RFC 9234 */
+      if (cl != 1)
+        goto err;
+
+      /* Reserved value */
+      if (pos[2] == BGP_ROLE_UNDEFINED)
+      { err_subcode = 11; goto err; }
+
+      /* Multiple inconsistent values */
+      if ((caps->role != BGP_ROLE_UNDEFINED) && (caps->role != pos[2]))
+      { err_subcode = 11; goto err; }
+
+      caps->role = pos[2];
+      break;
+
     case 64: /* Graceful restart capability, RFC 4724 */
       if (cl % 4 != 2)
 	goto err;
@@ -638,7 +665,7 @@ bgp_read_capabilities(struct bgp_conn *conn, byte *pos, int len)
 
 err:
   mb_free(caps);
-  bgp_error(conn, 2, 0, NULL, 0);
+  bgp_error(conn, 2, err_subcode, NULL, 0);
   return -1;
 }
 
@@ -854,6 +881,22 @@ bgp_rx_open(struct bgp_conn *conn, byte *pkt, uint len)
     conn->received_as = asn;
   }
 
+  /* RFC 9234 4.2 - check role agreement */
+  u8 local_role = p->cf->local_role;
+  u8 neigh_role = caps->role;
+
+  if ((local_role != BGP_ROLE_UNDEFINED) &&
+      (neigh_role != BGP_ROLE_UNDEFINED) &&
+      !((local_role == BGP_ROLE_PEER && neigh_role == BGP_ROLE_PEER) ||
+	(local_role == BGP_ROLE_CUSTOMER && neigh_role == BGP_ROLE_PROVIDER) ||
+	(local_role == BGP_ROLE_PROVIDER && neigh_role == BGP_ROLE_CUSTOMER) ||
+	(local_role == BGP_ROLE_RS_CLIENT && neigh_role == BGP_ROLE_RS_SERVER) ||
+	(local_role == BGP_ROLE_RS_SERVER && neigh_role == BGP_ROLE_RS_CLIENT)))
+  { bgp_error(conn, 2, 11, NULL, 0); return; }
+
+  if ((p->cf->require_roles) && (neigh_role == BGP_ROLE_UNDEFINED))
+  { bgp_error(conn, 2, 11, NULL, 0); return; }
+
   /* Check the other connection */
   other = (conn == &p->outgoing_conn) ? &p->incoming_conn : &p->outgoing_conn;
   switch (other->state)
@@ -2984,6 +3027,7 @@ static struct {
   { 2, 6, "Unacceptable hold time" },
   { 2, 7, "Required capability missing" }, /* [RFC5492] */
   { 2, 8, "No supported AFI/SAFI" }, /* This error msg is nonstandard */
+  { 2,11, "Role mismatch" }, /* From Open Policy, RFC 9234 */
   { 3, 0, "Invalid UPDATE message" },
   { 3, 1, "Malformed attribute list" },
   { 3, 2, "Unrecognized well-known attribute" },