[PATCH v2 1/2] Babel: Add option to support ecmp routes
Daniel Gröber
dxld at darkboxed.org
Mon May 9 14:38:59 CEST 2022
---
doc/bird.sgml | 25 ++++++++++++++++
proto/babel/babel.c | 70 +++++++++++++++++++++++++++++++++++++-------
proto/babel/babel.h | 5 ++++
proto/babel/config.Y | 3 ++
4 files changed, 92 insertions(+), 11 deletions(-)
diff --git a/doc/bird.sgml b/doc/bird.sgml
index 1580facd..d1e6376b 100644
--- a/doc/bird.sgml
+++ b/doc/bird.sgml
@@ -1865,6 +1865,7 @@ protocol babel [<name>] {
ipv4 { <channel config> };
ipv6 [sadr] { <channel config> };
randomize router id <switch>;
+ ecmp <switch> [limit <num>];
interface <interface pattern> {
type <wired|wireless>;
rxcost <number>;
@@ -1909,6 +1910,18 @@ protocol babel [<name>] {
router ID every time it starts up, which avoids this problem at the cost
of not having stable router IDs in the network. Default: no.
+ <tag><label id="babel-ecmp">ecmp <m>switch</m> [limit <m>number</m>]</tag>
+
+ Determines whether babel will emit ECMP (equal-cost multipath)
+ routes, allowing to load-balancing traffic across multiple paths. If
+ enabled the maximum number of next-hops to allow can be specified,
+ defaulting to 16.
+
+ When neibours are using a dynamic link-quality metric this is
+ unlikely to be useful. For best results <ref id="babel-type"
+ name="type wired"> should be used throughout the network to get what
+ amounts to a hop count metric.
+
<tag><label id="babel-type">type wired|wireless </tag>
This option specifies the interface type: Wired or wireless. On wired
interfaces a neighbor is considered unreachable after a small number of
@@ -1928,6 +1941,18 @@ protocol babel [<name>] {
selection and not local route selection. Default: 96 for wired interfaces,
256 for wireless.
+ <tag><label id="babel-ecmp">ecmp <m>switch</m> [limit <m>number</m>]</tag>
+
+ Determines whether babel will emit ECMP (equal-cost multipath)
+ routes, allowing to load-balancing traffic across multiple paths. If
+ enabled the maximum number of next-hops to allow can be specified,
+ defaulting to 16.
+
+ When neibours are using a dynamic link-quality metric this is
+ unlikely to be useful. For best results <ref id="babel-type"
+ name="type wired"> should be used throughout the network to get what
+ amounts to a hop count metric.
+
<tag><label id="babel-limit">limit <m/num/</tag>
BIRD keeps track of received Hello messages from each neighbor to
establish neighbor reachability. For wired type interfaces, this option
diff --git a/proto/babel/babel.c b/proto/babel/babel.c
index 4a7d550f..01ea3a44 100644
--- a/proto/babel/babel.c
+++ b/proto/babel/babel.c
@@ -623,6 +623,34 @@ done:
}
}
+/**
+ * babel_nexthop_insert - add next_hop of route to nexthop list
+ * @p: Babel protocol instance
+ * @r: Babel route
+ * @nhs: nexthop list head to append onto
+ * @nh: freshly allocated buffer to fill
+ */
+static void
+babel_nexthop_insert(
+ struct babel_proto *p,
+ struct babel_route *r,
+ struct nexthop **nhs,
+ struct nexthop *nh)
+{
+ nh->gw = r->next_hop;
+ nh->iface = r->neigh->ifa->iface;
+
+ /*
+ * If we cannot find a reachable neighbour, set the entry to be onlink. This
+ * makes it possible to, e.g., assign /32 addresses on a mesh interface and
+ * have routing work.
+ */
+ if (!neigh_find(&p->p, r->next_hop, r->neigh->ifa->iface, 0))
+ nh->flags = RNF_ONLINK;
+
+ nexthop_insert(nhs, nh);
+}
+
/**
* babel_announce_rte - announce selected route to the core
* @p: Babel protocol instance
@@ -635,6 +663,7 @@ done:
static void
babel_announce_rte(struct babel_proto *p, struct babel_entry *e)
{
+ struct babel_config *cf = (void *) p->p.cf;
struct babel_route *r = e->selected;
struct channel *c = (e->n.addr->type == NET_IP4) ? p->ip4_channel : p->ip6_channel;
@@ -645,18 +674,24 @@ babel_announce_rte(struct babel_proto *p, struct babel_entry *e)
.source = RTS_BABEL,
.scope = SCOPE_UNIVERSE,
.dest = RTD_UNICAST,
- .from = r->neigh->addr,
- .nh.gw = r->next_hop,
- .nh.iface = r->neigh->ifa->iface,
};
- /*
- * If we cannot find a reachable neighbour, set the entry to be onlink. This
- * makes it possible to, e.g., assign /32 addresses on a mesh interface and
- * have routing work.
- */
- if (!neigh_find(&p->p, r->next_hop, r->neigh->ifa->iface, 0))
- a0.nh.flags = RNF_ONLINK;
+ struct nexthop *nhs = NULL;
+ babel_nexthop_insert(p, r, &nhs, allocz(sizeof(struct nexthop)));
+ int num_nexthops = 1;
+
+ struct babel_route *cr;
+ WALK_LIST(cr, e->routes) {
+ if (cr == r || !cr->feasible || cr->metric != r->metric)
+ continue;
+
+ if (num_nexthops++ >= cf->max_nexthops)
+ break;
+
+ babel_nexthop_insert(p, cr, &nhs, allocz(sizeof(struct nexthop)));
+ }
+
+ a0.nh = *nhs;
rta *a = rta_lookup(&a0);
rte *rte = rte_get_temp(a);
@@ -736,6 +771,7 @@ babel_announce_retraction(struct babel_proto *p, struct babel_entry *e)
static void
babel_select_route(struct babel_proto *p, struct babel_entry *e, struct babel_route *mod)
{
+ struct babel_config *cf = (void *) p->p.cf;
struct babel_route *r, *best = e->selected;
/* Shortcut if only non-best was modified */
@@ -744,8 +780,10 @@ babel_select_route(struct babel_proto *p, struct babel_entry *e, struct babel_ro
/* Either select modified route, or keep old best route */
if ((mod->metric < (best ? best->metric : BABEL_INFINITY)) && mod->feasible)
best = mod;
- else
+ else if (cf->max_nexthops == 1)
return;
+ /* With ecmp one of the non-selected but equal metric routes might have
+ * changed so contine on with the announcement in that case. */
}
else
{
@@ -1879,6 +1917,16 @@ babel_reconfigure_iface(struct babel_proto *p, struct babel_iface *ifa, struct b
if (ifa->up)
babel_iface_kick_timer(ifa);
+ /* Update all routes to refresh ecmp settings. */
+ FIB_WALK(&p->ip6_rtable, struct babel_entry, e) {
+ babel_select_route(p, e, NULL);
+ }
+ FIB_WALK_END;
+ FIB_WALK(&p->ip4_rtable, struct babel_entry, e) {
+ babel_select_route(p, e, NULL);
+ }
+ FIB_WALK_END;
+
return 1;
}
diff --git a/proto/babel/babel.h b/proto/babel/babel.h
index 84feb085..46e268fd 100644
--- a/proto/babel/babel.h
+++ b/proto/babel/babel.h
@@ -62,6 +62,8 @@
#define BABEL_OVERHEAD (IP6_HEADER_LENGTH+UDP_HEADER_LENGTH)
#define BABEL_MIN_MTU (512 + BABEL_OVERHEAD)
+#define BABEL_DEFAULT_ECMP_LIMIT 16
+
#define BABEL_AUTH_NONE 0
#define BABEL_AUTH_MAC 1
@@ -120,6 +122,9 @@ struct babel_config {
list iface_list; /* List of iface configs (struct babel_iface_config) */
uint hold_time; /* Time to hold stale entries and unreachable routes */
u8 randomize_router_id;
+ u8 max_nexthops; /* Maximum number of nexthops to
+ install. Defaults to 1. It's >1 if
+ ECMP is enabled. */
struct channel_config *ip4_channel;
struct channel_config *ip6_channel;
diff --git a/proto/babel/config.Y b/proto/babel/config.Y
index 05210fa4..92e754cd 100644
--- a/proto/babel/config.Y
+++ b/proto/babel/config.Y
@@ -36,6 +36,7 @@ babel_proto_start: proto_start BABEL
this_proto = proto_config_new(&proto_babel, $1);
init_list(&BABEL_CFG->iface_list);
BABEL_CFG->hold_time = 1 S_;
+ BABEL_CFG->max_nexthops = 1;
};
babel_proto_item:
@@ -43,6 +44,8 @@ babel_proto_item:
| proto_channel
| INTERFACE babel_iface
| RANDOMIZE ROUTER ID bool { BABEL_CFG->randomize_router_id = $4; }
+ | ECMP bool { BABEL_CFG->max_nexthops = $2 ? BABEL_DEFAULT_ECMP_LIMIT : 1; }
+ | ECMP bool LIMIT expr { BABEL_CFG->max_nexthops = $2 ? $4 : 1; }
;
babel_proto_opts:
--
2.30.2
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