BGP: Add option 'next hop prefer global'

Add BGP channel option 'next hop prefer global' that modifies BGP
recursive next hop resolution to use global next hop IPv6 address instead
of link-local next hop IPv6 address for immediate next hop of received
routes.

4 files changed, 13 insertions, 2 deletions

diff --git a/proto/bgp/bgp.c b/proto/bgp/bgp.c
index e1e0d796..ad78d5e5 100644
--- a/proto/bgp/bgp.c
+++ b/proto/bgp/bgp.c
@@ -2037,6 +2037,10 @@ bgp_postconfig(struct proto_config *CF)
     if (!cc->gw_mode)
       cc->gw_mode = cf->multihop ? GW_RECURSIVE : GW_DIRECT;
 
+    /* Different default for next_hop_prefer */
+    if (!cc->next_hop_prefer)
+      cc->next_hop_prefer = (cc->gw_mode == GW_DIRECT) ? NHP_GLOBAL : NHP_LOCAL;
+
     /* Defaults based on proto config */
     if (cc->gr_able == 0xff)
       cc->gr_able = (cf->gr_mode == BGP_GR_ABLE);
@@ -2167,6 +2171,7 @@ bgp_channel_reconfigure(struct channel *C, struct channel_config *CC, int *impor
     return 0;
 
   if ((new->gw_mode != old->gw_mode) ||
+      (new->next_hop_prefer != old->next_hop_prefer) ||
       (new->aigp != old->aigp) ||
       (new->cost != old->cost))
   {
diff --git a/proto/bgp/bgp.h b/proto/bgp/bgp.h
index 5d0e9791..eda5d229 100644
--- a/proto/bgp/bgp.h
+++ b/proto/bgp/bgp.h
@@ -145,6 +145,7 @@ struct bgp_channel_config {
   ip_addr next_hop_addr;		/* Local address for NEXT_HOP attribute */
   u8 next_hop_self;			/* Always set next hop to local IP address (NH_*) */
   u8 next_hop_keep;			/* Do not modify next hop attribute (NH_*) */
+  u8 next_hop_prefer;			/* Prefer global or link-local next hop (NHP_*) */
   u8 mandatory;				/* Channel is mandatory in capability negotiation */
   u8 gw_mode;				/* How we compute route gateway from next_hop attr, see GW_* */
   u8 secondary;				/* Accept also non-best routes (i.e. RA_ACCEPTED) */
@@ -187,6 +188,9 @@ struct bgp_channel_config {
 #define GW_DIRECT		1
 #define GW_RECURSIVE		2
 
+#define NHP_GLOBAL		1
+#define NHP_LOCAL		2
+
 #define BGP_ADD_PATH_RX		1
 #define BGP_ADD_PATH_TX		2
 #define BGP_ADD_PATH_FULL	3
diff --git a/proto/bgp/config.Y b/proto/bgp/config.Y
index cb410a5e..2294119e 100644
--- a/proto/bgp/config.Y
+++ b/proto/bgp/config.Y
@@ -32,7 +32,7 @@ CF_KEYWORDS(BGP, LOCAL, NEIGHBOR, AS, HOLD, TIME, CONNECT, RETRY, KEEPALIVE,
 	LIVED, STALE, IMPORT, IBGP, EBGP, MANDATORY, INTERNAL, EXTERNAL, SETS,
 	DYNAMIC, RANGE, NAME, DIGITS, BGP_AIGP, AIGP, ORIGINATE, COST, ENFORCE,
 	FIRST, FREE, VALIDATE, BASE, ROLE, ROLES, PEER, PROVIDER, CUSTOMER,
-	RS_SERVER, RS_CLIENT, REQUIRE, BGP_OTC)
+	RS_SERVER, RS_CLIENT, REQUIRE, BGP_OTC, PREFER, GLOBAL)
 
 %type <i> bgp_nh
 %type <i32> bgp_afi
@@ -263,6 +263,7 @@ bgp_channel_item:
  | NEXT HOP ADDRESS ipa { BGP_CC->next_hop_addr = $4; }
  | NEXT HOP SELF bgp_nh { BGP_CC->next_hop_self = $4; }
  | NEXT HOP KEEP bgp_nh { BGP_CC->next_hop_keep = $4; }
+ | NEXT HOP PREFER GLOBAL { BGP_CC->next_hop_prefer = NHP_GLOBAL; }
  | MANDATORY bool { BGP_CC->mandatory = $2; }
  | MISSING LLADDR bgp_lladdr { log(L_WARN "%s.%s: Missing lladdr option is deprecated and ignored, remove it", this_proto->name, this_channel->name); }
  | GATEWAY DIRECT { BGP_CC->gw_mode = GW_DIRECT; }
diff --git a/proto/bgp/packets.c b/proto/bgp/packets.c
index 8087608a..c464e9c7 100644
--- a/proto/bgp/packets.c
+++ b/proto/bgp/packets.c
@@ -1020,7 +1020,8 @@ bgp_apply_next_hop(struct bgp_parse_state *s, rta *a, ip_addr gw, ip_addr ll)
       WITHDRAW(BAD_NEXT_HOP " - zero address");
 
     rtable *tab = ipa_is_ip4(gw) ? c->igp_table_ip4 : c->igp_table_ip6;
-    s->hostentry = rt_get_hostentry(tab, gw, ll, c->c.table);
+    ip_addr lla = (c->cf->next_hop_prefer == NHP_LOCAL) ? ll : IPA_NONE;
+    s->hostentry = rt_get_hostentry(tab, gw, lla, c->c.table);
 
     if (!s->mpls)
       rta_apply_hostentry(a, s->hostentry, NULL);