bgpd: add 'set as-path exclude all' command

It is not possible to flush all the incoming as-path list
from a given BGP update.

Add a route-map set command to remove all as-paths
from a given AS path. Add the necessary tests.

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>

bgpd/bgp_aspath.c

@@ -1598,6 +1598,24 @@ struct aspath *aspath_filter_exclude(struct aspath *source,
 	return newpath;
 }
 
+struct aspath *aspath_filter_exclude_all(struct aspath *source)
+{
+	struct aspath *newpath;
+
+	newpath = aspath_new(source->asnotation);
+
+	aspath_str_update(newpath, false);
+	/* We are happy returning even an empty AS_PATH, because the
+	 * administrator
+	 * might expect this very behaviour. There's a mean to avoid this, if
+	 * necessary,
+	 * by having a match rule against certain AS_PATH regexps in the
+	 * route-map index.
+	 */
+	aspath_free(source);
+	return newpath;
+}
+
 /* Add specified AS to the leftmost of aspath. */
 static struct aspath *aspath_add_asns(struct aspath *aspath, as_t asno,
 				      uint8_t type, unsigned num)

bgpd/bgp_aspath.h

@@ -76,6 +76,7 @@ extern struct aspath *aspath_aggregate(struct aspath *as1, struct aspath *as2);
 extern struct aspath *aspath_prepend(struct aspath *as1, struct aspath *as2);
 extern struct aspath *aspath_filter_exclude(struct aspath *source,
 					    struct aspath *exclude_list);
+extern struct aspath *aspath_filter_exclude_all(struct aspath *source);
 extern struct aspath *aspath_add_seq_n(struct aspath *aspath, as_t asno,
 				       unsigned num);
 extern struct aspath *aspath_add_seq(struct aspath *aspath, as_t asno);

bgpd/bgp_routemap.c

@@ -2300,6 +2300,31 @@ static const struct route_map_rule_cmd route_set_aspath_prepend_cmd = {
 };
 
 /* `set as-path exclude ASn' */
+struct aspath_exclude {
+	struct aspath *aspath;
+	bool exclude_all;
+};
+
+static void *route_aspath_exclude_compile(const char *arg)
+{
+	struct aspath_exclude *ase;
+	const char *str = arg;
+
+	ase = XCALLOC(MTYPE_ROUTE_MAP_COMPILED, sizeof(struct aspath_exclude));
+	if (!strmatch(str, "all"))
+		ase->aspath = aspath_str2aspath(str, bgp_get_asnotation(NULL));
+	else
+		ase->exclude_all = true;
+	return ase;
+}
+
+static void route_aspath_exclude_free(void *rule)
+{
+	struct aspath_exclude *ase = rule;
+
+	aspath_free(ase->aspath);
+	XFREE(MTYPE_ROUTE_MAP_COMPILED, ase);
+}
 
 /* For ASN exclude mechanism.
  * Iterate over ASns requested and filter them from the given AS_PATH one by
@@ -2309,16 +2334,28 @@ static const struct route_map_rule_cmd route_set_aspath_prepend_cmd = {
 static enum route_map_cmd_result_t
 route_set_aspath_exclude(void *rule, const struct prefix *dummy, void *object)
 {
-	struct aspath *new_path, *exclude_path;
+	struct aspath *new_path;
 	struct bgp_path_info *path;
+	struct aspath_exclude *ase = rule;
 
-	exclude_path = rule;
 	path = object;
+
+	if (path->peer->sort != BGP_PEER_EBGP) {
+		zlog_warn(
+			"`set as-path exclude` is supported only for EBGP peers");
+		return RMAP_NOOP;
+	}
+
 	if (path->attr->aspath->refcnt)
 		new_path = aspath_dup(path->attr->aspath);
 	else
 		new_path = path->attr->aspath;
-	path->attr->aspath = aspath_filter_exclude(new_path, exclude_path);
+
+	if (ase->aspath)
+		path->attr->aspath =
+			aspath_filter_exclude(new_path, ase->aspath);
+	else if (ase->exclude_all)
+		path->attr->aspath = aspath_filter_exclude_all(new_path);
 
 	return RMAP_OKAY;
 }
@@ -2327,8 +2364,8 @@ route_set_aspath_exclude(void *rule, const struct prefix *dummy, void *object)
 static const struct route_map_rule_cmd route_set_aspath_exclude_cmd = {
 	"as-path exclude",
 	route_set_aspath_exclude,
-	route_aspath_compile,
-	route_aspath_free,
+	route_aspath_exclude_compile,
+	route_aspath_exclude_free,
 };
 
 /* `set as-path replace AS-PATH` */
@@ -5910,6 +5947,32 @@ DEFUN_YANG (set_aspath_exclude,
 	return ret;
 }
 
+DEFPY_YANG(set_aspath_exclude_all, set_aspath_exclude_all_cmd,
+	   "[no$no] set as-path exclude all$all",
+	   NO_STR SET_STR
+	   "Transform BGP AS-path attribute\n"
+	   "Exclude from the as-path\n"
+	   "Exclude all AS numbers from the as-path\n")
+{
+	int ret;
+	const char *xpath =
+		"./set-action[action='frr-bgp-route-map:as-path-exclude']";
+	char xpath_value[XPATH_MAXLEN];
+
+	if (no)
+		nb_cli_enqueue_change(vty, xpath, NB_OP_DESTROY, NULL);
+	else {
+		nb_cli_enqueue_change(vty, xpath, NB_OP_CREATE, NULL);
+		snprintf(xpath_value, sizeof(xpath_value),
+			 "%s/rmap-set-action/frr-bgp-route-map:exclude-as-path",
+			 xpath);
+		nb_cli_enqueue_change(vty, xpath_value, NB_OP_MODIFY, all);
+	}
+	ret = nb_cli_apply_changes(vty, NULL);
+
+	return ret;
+}
+
 DEFUN_YANG (no_set_aspath_exclude,
 	    no_set_aspath_exclude_cmd,
 	    "no set as-path exclude ASNUM...",
@@ -7436,6 +7499,7 @@ void bgp_route_map_init(void)
 	install_element(RMAP_NODE, &set_aspath_prepend_asn_cmd);
 	install_element(RMAP_NODE, &set_aspath_prepend_lastas_cmd);
 	install_element(RMAP_NODE, &set_aspath_exclude_cmd);
+	install_element(RMAP_NODE, &set_aspath_exclude_all_cmd);
 	install_element(RMAP_NODE, &set_aspath_replace_asn_cmd);
 	install_element(RMAP_NODE, &no_set_aspath_prepend_cmd);
 	install_element(RMAP_NODE, &no_set_aspath_prepend_lastas_cmd);

doc/user/bgp.rst

@@ -2106,6 +2106,11 @@ Using AS Path in Route Map
    Replace a specific AS number to local AS number. ``any`` replaces each
    AS number in the AS-PATH with the local AS number.
 
+.. clicmd:: set as-path exclude all
+
+   Remove all AS numbers from the AS_PATH of the BGP path's NLRI. The no form of
+   this command removes this set operation from the route-map.
+
 .. _bgp-communities-attribute:
 
 Communities Attribute

tests/topotests/bgp_set_aspath_exclude/r1/bgpd.conf

@@ -0,0 +1,17 @@
+!
+router bgp 65001
+ no bgp ebgp-requires-policy
+ neighbor 192.168.1.2 remote-as external
+ neighbor 192.168.1.2 timers 3 10
+ address-family ipv4 unicast
+  neighbor 192.168.1.2 route-map r2 in
+ exit-address-family
+!
+ip prefix-list p1 seq 5 permit 172.16.255.31/32
+!
+route-map r2 permit 10
+ match ip address prefix-list p1
+ set as-path exclude 65003
+route-map r2 permit 20
+ set as-path exclude all
+!

tests/topotests/bgp_set_aspath_exclude/r1/zebra.conf

@@ -0,0 +1,6 @@
+!
+interface r1-eth0
+ ip address 192.168.1.1/24
+!
+ip forwarding
+!

tests/topotests/bgp_set_aspath_exclude/r2/bgpd.conf

@@ -0,0 +1,8 @@
+!
+router bgp 65002
+ no bgp ebgp-requires-policy
+ neighbor 192.168.1.1 remote-as external
+ neighbor 192.168.1.1 timers 3 10
+ neighbor 192.168.2.1 remote-as external
+ neighbor 192.168.2.1 timers 3 10
+!

tests/topotests/bgp_set_aspath_exclude/r2/zebra.conf

@@ -0,0 +1,9 @@
+!
+interface r2-eth0
+ ip address 192.168.1.2/24
+!
+interface r2-eth1
+ ip address 192.168.2.2/24
+!
+ip forwarding
+!

tests/topotests/bgp_set_aspath_exclude/r3/bgpd.conf

@@ -0,0 +1,9 @@
+!
+router bgp 65003
+ no bgp ebgp-requires-policy
+ neighbor 192.168.2.2 remote-as external
+ neighbor 192.168.2.2 timers 3 10
+ address-family ipv4 unicast
+  redistribute connected
+ exit-address-family
+!

tests/topotests/bgp_set_aspath_exclude/r3/zebra.conf

@@ -0,0 +1,10 @@
+!
+int lo
+ ip address 172.16.255.31/32
+ ip address 172.16.255.32/32
+!
+interface r3-eth0
+ ip address 192.168.2.1/24
+!
+ip forwarding
+!

tests/topotests/bgp_set_aspath_exclude/test_bgp_set_aspath_exclude.py

@@ -0,0 +1,89 @@
+#!/usr/bin/env python
+# SPDX-License-Identifier: ISC
+#
+# test_bgp_set_aspath_exclude.py
+#
+# Copyright 2023 by 6WIND S.A.
+#
+
+"""
+Test if `set as-path exclude` is working correctly for route-maps.
+"""
+
+import os
+import sys
+import json
+import pytest
+import functools
+
+CWD = os.path.dirname(os.path.realpath(__file__))
+sys.path.append(os.path.join(CWD, "../"))
+
+# pylint: disable=C0413
+from lib import topotest
+from lib.topogen import Topogen, TopoRouter, get_topogen
+
+
+pytestmark = [pytest.mark.bgpd]
+
+
+def build_topo(tgen):
+    for routern in range(1, 5):
+        tgen.add_router("r{}".format(routern))
+
+    switch = tgen.add_switch("s1")
+    switch.add_link(tgen.gears["r1"])
+    switch.add_link(tgen.gears["r2"])
+
+    switch = tgen.add_switch("s2")
+    switch.add_link(tgen.gears["r2"])
+    switch.add_link(tgen.gears["r3"])
+
+
+def setup_module(mod):
+    tgen = Topogen(build_topo, mod.__name__)
+    tgen.start_topology()
+
+    router_list = tgen.routers()
+
+    for i, (rname, router) in enumerate(router_list.items(), 1):
+        router.load_config(
+            TopoRouter.RD_ZEBRA, os.path.join(CWD, "{}/zebra.conf".format(rname))
+        )
+        router.load_config(
+            TopoRouter.RD_BGP, os.path.join(CWD, "{}/bgpd.conf".format(rname))
+        )
+
+    tgen.start_router()
+
+
+def teardown_module(mod):
+    tgen = get_topogen()
+    tgen.stop_topology()
+
+
+def test_bgp_set_aspath_exclude():
+    tgen = get_topogen()
+
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    def _bgp_converge(router):
+        output = json.loads(router.vtysh_cmd("show bgp ipv4 unicast json"))
+        expected = {
+            "routes": {
+                "172.16.255.31/32": [{"path": "65002"}],
+                "172.16.255.32/32": [{"path": ""}],
+            }
+        }
+        return topotest.json_cmp(output, expected)
+
+    test_func = functools.partial(_bgp_converge, tgen.gears["r1"])
+    _, result = topotest.run_and_expect(test_func, None, count=30, wait=0.5)
+
+    assert result is None, "Failed overriding incoming AS-PATH with route-map"
+
+
+if __name__ == "__main__":
+    args = ["-s"] + sys.argv[1:]
+    sys.exit(pytest.main(args))