D-Link DES-3828 Product Manual - Page 195

xStack DES-3800 Series Layer 3 Stackable Fast Ethernet Managed Switch CLI Manual 27 IGMP COMMANDS IGMP or Internet Group Management Protocol is a protocol implemented by systems utilizing IPv4 to collect the membership information needed by the multicast routing protocol through various query messages sent out from the router or switch. Computers and network devices that want to receive multicast transmissions need to inform nearby routers that they will become members of a multicast group. The Internet Group Management Protocol (IGMP) is used to communicate this information. IGMP is also used to periodically check the multicast group for members that are no longer active. In the case where there is more than one multicast router on a subnetwork, one router is elected as the 'querier'. This router then keeps track of the membership of the multicast groups that have active members. The information received from IGMP is then used to determine if multicast packets should be forwarded to a given subnetwork or not. The router can check, using IGMP, to see if there is at least one member of a multicast group on a given subnetwork. If there are no members on a subnetwork, packets will not be forwarded to that subnetwork. The current release of the xStack DES-3800 Series switches now implements IGMPv3. Improvements of IGMPv3 over version 2 include: • The introduction of the SSM or Source Specific Multicast. In previous versions of IGMP, the host would receive all packets sent to the multicast group. Now, a host will receive packets only from a specific source or sources. This is done through the implementation of include and exclude filters used to accept or deny traffic from these specific sources. • In IGMPv2, Membership reports could contain only one multicast group whereas in v3, these reports can contain multiple multicast groups. • Leaving a multicast group could only be accomplished using a specific leave message in v2. In v3, leaving a multicast group is done through a Membership report which includes a block message in the group report packet. • For version 2, the host could respond to either a group query but in version 3, the host is now capable to answer queries specific to the group and the source. IGMPv3 is backwards compatible with other versions of IGMP and all IGMP protocols must be used in conjunction with PIM-DM or DVMRP for optimal use. The IGMP commands in the Command Line Interface (CLI) are listed (along with the appropriate parameters) in the following table. Command config igmp show igmp show igmp group Parameters [ipif | all] {version | query_interval | max_response_time | robustness_variable | last_member_query_interval | state [enable | disable]} {ipif } {group | ipif } Each command is listed, in detail, in the following sections. 191