# HG changeset patch
# User Roy Marples <roy@marples.name>
# Date 1603711194 0
# Node ID 8c0e5dc3482466871890796e68aa02a2c9094cfa
# Parent  357fddea93659cefdd23633dea8e90d711c5b3aa
DHCP: Implement IPv6-Only Preferred option, RFC 8925.

Enable it like so in dhcpcd.conf:
option ipv6_only_preferred

diff -r 357fddea9365 -r 8c0e5dc34824 src/dhcp.c
--- a/src/dhcp.c	Sun Oct 25 15:30:13 2020 +0000
+++ b/src/dhcp.c	Mon Oct 26 11:19:54 2020 +0000
@@ -2926,6 +2926,8 @@
 	unsigned int i;
 	char *msg;
 	bool bootp_copied;
+	uint32_t v6only_time = 0;
+	bool use_v6only = false;
 #ifdef AUTH
 	const uint8_t *auth;
 	size_t auth_len;
@@ -3143,6 +3145,23 @@
 		}
 	}
 
+	if (has_option_mask(ifo->requestmask, DHO_IPV6_PREFERRED_ONLY)) {
+		if (get_option_uint32(ifp->ctx, &v6only_time, bootp, bootp_len,
+		    DHO_IPV6_PREFERRED_ONLY) == 0 &&
+		    (state->state == DHS_DISCOVER || state->state == DHS_REBOOT))
+		{
+			char v6msg[128];
+
+			use_v6only = true;
+			if (v6only_time < MIN_V6ONLY_WAIT)
+				v6only_time = MIN_V6ONLY_WAIT;
+			snprintf(v6msg, sizeof(v6msg),
+			    "IPv6-Only Preferred received (%u seconds)",
+			    v6only_time);
+			LOGDHCP(LOG_INFO, v6msg);
+		}
+	}
+
 	/* DHCP Auto-Configure, RFC 2563 */
 	if (type == DHCP_OFFER && bootp->yiaddr == 0) {
 		LOGDHCP(LOG_WARNING, "no address given");
@@ -3177,12 +3196,22 @@
 			}
 			eloop_timeout_delete(ifp->ctx->eloop, NULL, ifp);
 			eloop_timeout_add_sec(ifp->ctx->eloop,
-			    DHCP_MAX, dhcp_discover, ifp);
+			    use_v6only ? v6only_time : DHCP_MAX,
+			    dhcp_discover, ifp);
 		}
 #endif
 		return;
 	}
 
+	if (use_v6only) {
+		dhcp_drop(ifp, "EXPIRE");
+		dhcp_unlink(ifp->ctx, state->leasefile);
+		eloop_timeout_delete(ifp->ctx->eloop, NULL, ifp);
+		eloop_timeout_add_sec(ifp->ctx->eloop, v6only_time,
+		    dhcp_discover, ifp);
+		return;
+	}
+
 	/* Ensure that the address offered is valid */
 	if ((type == 0 || type == DHCP_OFFER || type == DHCP_ACK) &&
 	    (bootp->ciaddr == INADDR_ANY || bootp->ciaddr == INADDR_BROADCAST)
diff -r 357fddea9365 -r 8c0e5dc34824 src/dhcp.h
--- a/src/dhcp.h	Sun Oct 25 15:30:13 2020 +0000
+++ b/src/dhcp.h	Mon Oct 26 11:19:54 2020 +0000
@@ -116,6 +116,7 @@
 	DHO_RAPIDCOMMIT            = 80,  /* RFC 4039 */
 	DHO_FQDN                   = 81,
 	DHO_AUTHENTICATION         = 90,  /* RFC 3118 */
+	DHO_IPV6_PREFERRED_ONLY    = 108, /* RFC 8925 */
 	DHO_AUTOCONFIGURE          = 116, /* RFC 2563 */
 	DHO_DNSSEARCH              = 119, /* RFC 3397 */
 	DHO_CSR                    = 121, /* RFC 3442 */
@@ -139,6 +140,8 @@
 	FQDN_BOTH       = 0x31
 };
 
+#define	MIN_V6ONLY_WAIT		300 /* seconds, RFC 8925 */
+
 /* Sizes for BOOTP options */
 #define	BOOTP_CHADDR_LEN	 16
 #define	BOOTP_SNAME_LEN		 64
diff -r 357fddea9365 -r 8c0e5dc34824 src/dhcpcd-definitions.conf
--- a/src/dhcpcd-definitions.conf	Sun Oct 25 15:30:13 2020 +0000
+++ b/src/dhcpcd-definitions.conf	Mon Oct 26 11:19:54 2020 +0000
@@ -172,6 +172,9 @@
 
 # Options 102-115 are unused, RFC3679
 
+# DHCP IPv6-Only Preferred, RFC8925
+define 108	uint32			ipv6_only_preferred
+
 # DHCP Auto-Configuration, RFC2563
 define 116	byte			auto_configure