frr: add basic multipath support

Using the new nexthop type group, allow multiple nexthop
as a gateway from frr.

The following zebra conf:
!
ip route 192.168.1.20/32 cv0
ip route 192.168.1.20/32 192.168.210.3
ip route 192.168.1.20/32 192.168.210.254
!

translates into these rib nexthops:
ID: 35 (zebra)
     RefCnt: 2
     Uptime: 00:00:07
     VRF: default(No AFI)
     Nexthop Count: 3
     Valid, Installed
     Depends: (20) (24) (30)
           is directly connected, cv0 (vrf default), weight 1
           via 192.168.210.3, cv0 (vrf default), weight 1
           via 192.168.210.254, cv0 (vrf default), weight 1

With grout displays the proper NHs:
grout# nexthop type group
VRF  ID  ORIGIN  IFACE  TYPE   INFO
0    35  user           group  id(20/1) id(24/1) id(30/1)

Signed-off-by: Christophe Fontaine <[email protected]>

Author: christophefontaine

frr/rt_grout.c

@@ -289,6 +289,12 @@ static int grout_gr_nexthop_to_frr_nexthop(
 		nexthop_add_srv6_seg6(nh, (void *)sr6->seglist, sr6->n_seglist, encap_behavior);
 		break;
 	}
+	case GR_NH_T_GROUP:
+		nh->ifindex = gr_nh->iface_id;
+		nh->vrf_id = gr_nh->vrf_id;
+		*nh_family = AF_UNSPEC;
+		nh->weight = 1;
+		break;
 	default:
 		gr_log_err(
 			"sync %s nexthops from grout not supported", gr_nh_type_name(gr_nh->type)
@@ -572,12 +578,42 @@ enum zebra_dplane_result grout_add_del_route(struct zebra_dplane_ctx *ctx) {
 	return ZEBRA_DPLANE_REQUEST_SUCCESS;
 }
 
+static enum zebra_dplane_result grout_add_nexthop_group(struct zebra_dplane_ctx *ctx) {
+	uint32_t nh_id = dplane_ctx_get_nhe_id(ctx);
+	struct gr_nexthop_info_group *group;
+	struct gr_nh_add_req *req = NULL;
+	size_t len;
+
+	len = sizeof(*req) + sizeof(*group)
+		+ dplane_ctx_get_nhe_nh_grp_count(ctx) * sizeof(group->members[0]);
+	if ((req = calloc(1, len)) == NULL)
+		return ZEBRA_DPLANE_REQUEST_FAILURE;
+
+	group = (struct gr_nexthop_info_group *)req->nh.info;
+	group->n_members = dplane_ctx_get_nhe_nh_grp_count(ctx);
+
+	req->exist_ok = true;
+	req->nh.nh_id = nh_id;
+	req->nh.type = GR_NH_T_GROUP;
+	req->nh.origin = zebra2origin(dplane_ctx_get_nhe_type(ctx));
+
+	const struct nh_grp *nhs = dplane_ctx_get_nhe_nh_grp(ctx);
+	for (size_t i = 0; i < group->n_members; i++) {
+		group->members[i].nh_id = nhs[i].id;
+		group->members[i].weight = nhs[i].weight;
+	}
+
+	if (grout_client_send_recv(GR_NH_ADD, len, req, NULL) < 0)
+		return ZEBRA_DPLANE_REQUEST_FAILURE;
+
+	return ZEBRA_DPLANE_REQUEST_SUCCESS;
+}
+
 static enum zebra_dplane_result grout_del_nexthop(uint32_t nh_id) {
 	struct gr_nh_del_req req = {.missing_ok = true, .nh_id = nh_id};
 
 	if (grout_client_send_recv(GR_NH_DEL, sizeof(req), &req, NULL) < 0)
 		return ZEBRA_DPLANE_REQUEST_FAILURE;
-
 	return ZEBRA_DPLANE_REQUEST_SUCCESS;
 }
 
@@ -762,15 +798,12 @@ enum zebra_dplane_result grout_add_del_nexthop(struct zebra_dplane_ctx *ctx) {
 		return ZEBRA_DPLANE_REQUEST_FAILURE;
 	}
 
-	if (dplane_ctx_get_nhe_nh_grp_count(ctx)) {
-		// next group are not supported in grout
-		gr_log_err("impossible to add/del nexthop grout %u (nhg not supported)", nh_id);
-		return ZEBRA_DPLANE_REQUEST_FAILURE;
-	}
-
 	if (dplane_ctx_get_op(ctx) == DPLANE_OP_NH_DELETE)
 		return grout_del_nexthop(nh_id);
 
+	if (dplane_ctx_get_nhe_nh_grp_count(ctx))
+		return grout_add_nexthop_group(ctx);
+
 	return grout_add_nexthop(nh_id, origin, dplane_ctx_get_nhe_ng(ctx)->nexthop);
 }
 

smoke/ip_loadbalance_frr_test.sh

@@ -0,0 +1,60 @@
+#!/bin/bash
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright (c) 2025 Christophe Fontaine
+
+#
+#                         |   p1 (.1.2)
+#  [p0 ns0] --- grout --- | ns1          lo
+#                         |   p2 (.2.2)
+#
+#
+#
+. $(dirname $0)/_init_frr.sh
+
+p0=${run_id}0
+p1=${run_id}1
+p2=${run_id}2
+
+create_interface $p0 f0:0d:ac:dc:00:00
+create_interface $p1 f0:0d:ac:dc:00:01
+create_interface $p2 f0:0d:ac:dc:00:02
+
+netns_add n-$p0
+	ip l set $p0 netns n-$p0
+	ip -n n-$p0 link set $p0 address ba:d0:ca:ca:00:00
+	ip -n n-$p0 link set $p0 up
+	ip -n n-$p0 link set lo up
+	ip -n n-$p0 addr add 172.16.0.2/24 dev $p0
+	ip -n n-$p0 route add default via 172.16.0.1
+
+netns_add n-$p1
+	ip l set $p1 netns n-$p1
+	ip l set $p2 netns n-$p1
+	ip -n n-$p1 link set lo up
+	ip -n n-$p1 addr add 192.0.0.2/32 dev lo
+	ip -n n-$p1 link set $p1 address ba:d0:ca:ca:00:01
+	ip -n n-$p1 link set $p1 up
+	ip -n n-$p1 addr add 172.16.1.2/24 dev $p1
+	ip -n n-$p1 link set $p2 address ba:d0:ca:ca:00:02
+	ip -n n-$p1 link set $p2 up
+	ip -n n-$p1 addr add 172.16.2.2/24 dev $p2
+
+set_ip_address $p0 172.16.0.1/24
+set_ip_address $p1 172.16.1.1/24
+set_ip_address $p2 172.16.2.1/24
+
+set_ip_route 192.0.0.0/24 172.16.1.2
+# Can't use set_ip_route a second time
+# as the helper will look for the route
+# --> Configure it manually
+vtysh <<-EOF
+	configure terminal
+	ip route 192.0.0.0/24 172.16.2.2
+EOF
+
+ip -n n-$p1 route add default via 172.16.1.1
+ip netns exec n-$p0  ping 192.0.0.2 -c 4
+
+ip -n n-$p1 route del default
+ip -n n-$p1 route add default via 172.16.2.1
+ip netns exec n-$p0  ping 192.0.0.2 -c 4

subprojects/packagefiles/frr/meson-add-dependency-definition.patch

@@ -103,7 +103,7 @@ index 0000000..d26e979
 +    '"' + srcdir + '/configure" ' +
 +    '--prefix="' + prefix + '" ' +
 +    '--with-moduledir="' + moduledir + '" ' +
-+    '--disable-doc --enable-multipath=1 ' +
++    '--disable-doc --enable-multipath=128 ' +
 +    '--disable-ripd --disable-ripngd --disable-ospfd --disable-ospf6d ' +
 +    '--disable-ldpd --disable-nhrpd --disable-eigrpd --disable-babeld  ' +
 +    '--disable-isisd --disable-pimd --disable-pim6d --disable-pbrd --disable-fabricd ' +