DHCP: Add support for option 108 "IPv6-Only Preferred" (RFC 8925)

Add a test file with DHCP option 108 in both the request and the reply,
provided by Bill.

Author: fxlb

print-bootp.c

@@ -183,6 +183,8 @@ struct bootp {
 /* RFC 2610 */
 #define	TAG_SLP_DA		((uint8_t)  78)
 #define	TAG_SLP_SCOPE		((uint8_t)  79)
+/* RFC 8925 */
+#define TAG_IPV6_ONLY_PREFERRED	((uint8_t) 108)
 /* RFC 2937 */
 #define	TAG_NS_SEARCH		((uint8_t) 117)
 /* RFC 3004 - The User Class Option for DHCP */
@@ -530,6 +532,7 @@ static const struct tok tag2str[] = {
 	{ TAG_NETINFO_PARENT_TAG, "aNITAG" },
 	{ TAG_URL,		"aURL" },
 	{ TAG_MUDURL,           "aMUD-URL" },
+	{ TAG_IPV6_ONLY_PREFERRED, "$IPv6-Only-Preferred" },
 	{ 0, NULL }
 };
 
@@ -1030,6 +1033,18 @@ rfc1048_print(netdissect_options *ndo,
 				}
 				break;
 
+			case TAG_IPV6_ONLY_PREFERRED:
+				/* this option should be 4 bytes long */
+				if (len != 4) {
+					ND_PRINT("[ERROR: length != 4 bytes]");
+					bp += len;
+					len = 0;
+				}
+				ND_PRINT("%u", GET_BE_U_4(bp));
+				bp += 4;
+				len -= 4;
+				break;
+
 			default:
 				ND_PRINT("[unknown special tag %u, size %u]",
 					  tag, len);

tests/TESTLIST

@@ -522,6 +522,7 @@ dhcp-rfc3004	dhcp-rfc3004.pcap	dhcp-rfc3004-v.out	-v
 dhcp-rfc4388	dhcp-rfc4388.pcap	dhcp-rfc4388.out	-v
 dhcp-rfc5859	dhcp-rfc5859.pcap	dhcp-rfc5859-v.out	-v
 dhcp-mud	dhcp-mud.pcap		dhcp-mud.out	-vv
+dhcp-option-108	dhcp-option-108.pcapng	dhcp-option-108.out	-v
 
 # VXLAN tests
 vxlan  vxlan.pcap  vxlan.out -e

tests/dhcp-option-108.out

@@ -0,0 +1,31 @@
+    1  2025-03-18 09:43:45.393317 IP (tos 0x0, ttl 255, id 50068, offset 0, flags [none], proto UDP (17), length 328)
+    0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 42:b4:44:b4:f0:ee, length 300, xid 0x9edf45b0, Flags [none]
+	  Client-Ethernet-Address 42:b4:44:b4:f0:ee
+	  Vendor-rfc1048 Extensions
+	    Magic Cookie 0x63825363
+	    DHCP-Message (53), length 1: Discover
+	    Parameter-Request (55), length 12: 
+	      Subnet-Mask (1), Classless-Static-Route (121), Default-Gateway (3), Domain-Name-Server (6)
+	      Domain-Name (15), IPv6-Only-Preferred (108), URL (114), Unknown (119)
+	      Unknown (252), LDAP (95), Netbios-Name-Server (44), Netbios-Node (46)
+	    MSZ (57), length 2: 1500
+	    Client-ID (61), length 7: ether 42:b4:44:b4:f0:ee
+	    Lease-Time (51), length 4: 7776000
+	    Hostname (12), length 10: "MacBookPro"
+    2  2025-03-18 09:43:45.399056 IP (tos 0x0, ttl 64, id 64867, offset 0, flags [none], proto UDP (17), length 351)
+    10.56.0.2.67 > 10.56.42.232.68: BOOTP/DHCP, Reply, length 323, hops 1, xid 0x9edf45b0, Flags [none]
+	  Your-IP 10.56.42.232
+	  Gateway-IP 10.56.0.2
+	  Client-Ethernet-Address 42:b4:44:b4:f0:ee
+	  Vendor-rfc1048 Extensions
+	    Magic Cookie 0x63825363
+	    DHCP-Message (53), length 1: Offer
+	    Subnet-Mask (1), length 4: 255.255.0.0
+	    Default-Gateway (3), length 4: 10.56.0.1
+	    Domain-Name-Server (6), length 8: 31.130.229.6,31.130.229.7
+	    Hostname (12), length 10: "macbookpro"
+	    Domain-Name (15), length 16: "meeting.ietf.org"
+	    Lease-Time (51), length 4: 3600
+	    Server-ID (54), length 4: 31.130.229.6
+	    Client-ID (61), length 7: ether 42:b4:44:b4:f0:ee
+	    IPv6-Only-Preferred (108), length 4: 900