From dff90f5889fe8e7e01cb3d5b20adca13dafe9f89 Mon Sep 17 00:00:00 2001
From: Igor Putovny <igor.putovny@nic.cz>
Date: Tue, 4 Nov 2025 15:15:54 +0100
Subject: [PATCH] RAdv: Add P-flag to prefer prefix delegation in DHCPv6

---
 doc/bird.sgml        | 5 +++++
 proto/radv/config.Y  | 3 ++-
 proto/radv/packets.c | 8 +++++---
 proto/radv/radv.h    | 1 +
 4 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/doc/bird.sgml b/doc/bird.sgml
index a61400ef8..68229cb9d 100644
--- a/doc/bird.sgml
+++ b/doc/bird.sgml
@@ -5741,6 +5741,11 @@ custom option type 38 value hex:0e:10:20:01:0d:b8:00:0a:00:0b:00:00:00:00;
 	This option specifies whether hosts may use the advertised prefix for
 	stateless autoconfiguration. Default: yes
 
+	<tag><label id="radv-prefix-pd-preferred">pd preferred<m/switch/</tag>
+	This option specifies whether hosts should use prefix delegation in DHCPv6
+	instead of using stateless address autoconfiguration (SLAAC).
+	Default: no.
+
 	<tag><label id="radv-prefix-valid-lifetime">valid lifetime <m/expr/ [sensitive <m/switch/]</tag>
 	This option specifies the time (in seconds) how long (after the
 	receipt of RA) the prefix information is valid, i.e., autoconfigured
diff --git a/proto/radv/config.Y b/proto/radv/config.Y
index 045675b11..cd54f10cc 100644
--- a/proto/radv/config.Y
+++ b/proto/radv/config.Y
@@ -42,7 +42,7 @@ CF_KEYWORDS(RADV, PREFIX, INTERFACE, MIN, MAX, RA, DELAY, INTERVAL, SOLICITED,
 	RETRANS, TIMER, CURRENT, HOP, LIMIT, DEFAULT, VALID, PREFERRED, MULT,
 	LIFETIME, SKIP, ONLINK, AUTONOMOUS, RDNSS, DNSSL, NS, DOMAIN, LOCAL,
 	TRIGGER, SENSITIVE, PREFERENCE, LOW, MEDIUM, HIGH, PROPAGATE, ROUTE,
-	ROUTES, RA_PREFERENCE, RA_LIFETIME, CUSTOM, OPTION, TYPE, VALUE)
+	ROUTES, RA_PREFERENCE, RA_LIFETIME, CUSTOM, OPTION, TYPE, VALUE, PD)
 
 CF_ENUM(T_ENUM_RA_PREFERENCE, RA_PREF_, LOW, MEDIUM, HIGH)
 
@@ -215,6 +215,7 @@ radv_prefix_item:
    SKIP bool { RADV_PREFIX->skip = $2; }
  | ONLINK bool { RADV_PREFIX->onlink = $2; }
  | AUTONOMOUS bool { RADV_PREFIX->autonomous = $2; }
+ | PD PREFERRED bool { RADV_PREFIX->pd_preferred = $3; }
  | VALID LIFETIME expr radv_sensitive {
      RADV_PREFIX->valid_lifetime = $3;
      if ($4 != (uint) -1) RADV_PREFIX->valid_lifetime_sensitive = $4;
diff --git a/proto/radv/packets.c b/proto/radv/packets.c
index 77c987949..25f43b1a3 100644
--- a/proto/radv/packets.c
+++ b/proto/radv/packets.c
@@ -44,8 +44,9 @@ struct radv_opt_prefix
   ip6_addr prefix;
 };
 
-#define OPT_PX_ONLINK 0x80
-#define OPT_PX_AUTONOMOUS 0x40
+#define OPT_PX_ONLINK		  0x80
+#define OPT_PX_AUTONOMOUS	  0x40
+#define OPT_PX_PD_PREFERRED	  0x10
 
 struct radv_opt_mtu
 {
@@ -307,7 +308,8 @@ radv_prepare_prefix(struct radv_iface *ifa, struct radv_prefix *px,
   op->length = 4;
   op->pxlen = px->prefix.pxlen;
   op->flags = (pc->onlink ? OPT_PX_ONLINK : 0) |
-    (pc->autonomous ? OPT_PX_AUTONOMOUS : 0);
+	      (pc->autonomous ? OPT_PX_AUTONOMOUS : 0) |
+	      (pc->pd_preferred ? OPT_PX_PD_PREFERRED : 0);
   op->valid_lifetime = (ifa->ra->active || !pc->valid_lifetime_sensitive) ?
     htonl(pc->valid_lifetime) : 0;
   op->preferred_lifetime = (ifa->ra->active || !pc->preferred_lifetime_sensitive) ?
diff --git a/proto/radv/radv.h b/proto/radv/radv.h
index ba4a1b6c7..83491f47e 100644
--- a/proto/radv/radv.h
+++ b/proto/radv/radv.h
@@ -101,6 +101,7 @@ struct radv_prefix_config
   u8 skip;			/* Do not include this prefix to RA */
   u8 onlink;			/* Standard options from RFC 4861 */
   u8 autonomous;
+  u8 pd_preferred;
   u32 valid_lifetime;
   u32 preferred_lifetime;
   u8 valid_lifetime_sensitive;	 /* Whether valid_lifetime depends on trigger */
-- 
2.47.3