2002-02-06 2025-03-28 The Internet Group Message Protocol (IGMP) has many messages that are identified by a "type" field. Note that the original definition of IGMP in divided this field into two 4-bit values, "version" and "type". This was decided to be too restrictive, so the fields were combined into a single 8-bit type space. Standards Action 0x00 Reserved 0x01-0x08 Reserved (Obsolete) 0x09-0x10 Unassigned 0x11 IGMP Membership Query 0x12 IGMPv1 Membership Report 0x13 DVMRP 0x14 PIM version 1 0x15 Cisco Trace Messages 0x16 IGMPv2 Membership Report 0x17 IGMPv2 Leave Group 0x1e Multicast Traceroute Response 0x1f Multicast Traceroute 0x22 IGMPv3 Membership Report 0x30 Multicast Router Advertisement 0x31 Multicast Router Solicitation 0x32 Multicast Router Termination 0xf0-0xff Reserved for experimentation Standards Action Many of these IGMP types have a "code" field. Here we list the types again with their assigned code fields. 0 IGMP Version 1 1-255 IGMP Version 2 or above Max Response Time 1 Probe 2 Route Report 3 Old Ask Neighbors 4 Old Neighbors Reply 5 Ask Neighbors 6 Neighbors Reply 7 Prune 8 Graft 9 Graft Ack 0 Query 1 Register 2 Register-Stop 3 Join/Prune 4 RP-Reachable 5 Assert 6 Graft 7 Graft Ack 8 Mode 0-65533 IETF Review 65534-65535 Experimental Use 0 variable No-op 1-65533 Unassigned 65534-65535 variable Reserved for Experimental Use Standards Action 0 E Extension 1-3 Unassigned Standards Action 0 E Extension 1-15 Unassigned Bill Fenner mailto:fenner&research.att.com