Remove policy scripts

Rhai made a decision about a route cost one to three microseconds,
some two hundred times what the same costs in Rust. That was bearable
where a function is asked once for an UPDATE, and is not where every
route is weighed against every peer, as it is when routes are passed
on. What is wanted of a policy (mark routes by where they came from,
mark what is announced, let communities say who is told what) needs no
language; it is to be configuration, done natively.

Kept from that work: route selection goes by a LOCAL_PREF that policy
set on a route from an external peer, and the lab's configuration can
be added to by a phase.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

testdata/policy.rhai

@@ -1,61 +0,0 @@
-// An example policy script; see "Policy scripts" in bin/bgp/README.md for
-// everything a function can read and change.
-//
-// A function is given a route and the peer it comes from (or goes to). It
-// may change the route, and returns whether the route is taken (or
-// announced). Which function is for which peer is said in the
-// configuration: import { function: "from_peer" }.
-//
-// Constants defined here are for every function below.
-
-// Where a route was learned: what the rules for announcing it go by.
-const LEARNED_FROM = #{
-    customer: "65000:1000",
-    peer: "65000:2000",
-    provider: "65000:3000",
-    route_server: "65000:2000",
-};
-
-// A customer's route is preferred to a peer's, and that to a provider's:
-// the first earns money, the last costs it.
-const PREFERENCE = #{ customer: 300, peer: 200, route_server: 200, provider: 100 };
-
-const BLACKHOLE = "65535:666";
-const NO_EXPORT = "65535:65281";
-
-// Routes on their way in.
-fn from_peer(route, peer) {
-    // Not ours to act on, from just anyone.
-    if route.has_community(BLACKHOLE) { return false; }
-
-    // Marks in our own range mean something here: nobody else's word for
-    // them is taken.
-    route.remove_community("65000:*");
-    if peer.role in LEARNED_FROM {
-        route.add_community(LEARNED_FROM[peer.role]);
-        route.local_pref = PREFERENCE[peer.role];
-    }
-
-    // A peer can ask to be a last resort: 65000:80 on a route of its own.
-    if route.has_community(peer.asn % 65536, 80) {
-        route.local_pref = 80;
-    }
-    true
-}
-
-// Routes on their way out.
-fn to_peer(route, peer) {
-    if route.has_community(NO_EXPORT) { return false; }
-
-    // Only customers are told what we learned from peers and providers.
-    let from_above = route.has_community("65000:2000") || route.has_community("65000:3000");
-    if from_above && peer.role != "customer" { return false; }
-
-    // Our marks are our own business.
-    route.remove_community("65000:*");
-
-    // Traffic from this one is wanted by another way: the path looks
-    // longer to it.
-    if peer.name == "backup-transit" { route.prepend(2); }
-    true
-}

testdata/server.textpb

@@ -48,13 +48,7 @@ peers {
         # as generated from the routing registries.
         # prefixes { prefix: "193.0.0.0/21" max_length: 24 }
         # origin_asns: 3333
-        # And then the operator's own rules: a function of the policy
-        # script (see `policy` below), which may refuse the route or mark
-        # and rank it.
-        # function: "from_peer"
     }
-    # What the peer is told also goes through a function of the script.
-    # export { function: "to_peer" }
 }
 connect_retry_seconds: 5
 
@@ -71,11 +65,6 @@ originate {
     large_communities: "65000:1:2"
 }
 
-# The operator's own rules for routes, as a script beside this file; see
-# policy.rhai here for an example, and "Policy scripts" in
-# bin/bgp/README.md. `bgp --check` reads it and says what is wrong.
-# policy { path: "policy.rhai" }
-
 # Validation with the RPKI: refuse routes whose origin AS is not the one the
 # holder of the addresses authorised, and, from peers with a role, routes
 # whose AS path is a leak. Point it at a validator's RTR server.