Multicast statistics

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The Multicast module analyzes IGMP and MLD multicast management packets and shows detailed information about multicast groups and their members. IGMPv1, v2, v3 for IPv4 and ICMPv6 sub-protocols MLDv1 and v2 for IPv6 are supported.


Multicast group management message types


Several types of multicast group management messages exist:

  • Join: A member joins a multicast group and is interested in receiving all traffic for that group.
It is sent as a reply to a query or as soon as the member joins the group. For IGMPv3 and MLDv2, a join is a membership report with either an empty exclude list or a non-empty include list of sources that send packets to that multicast group.


  • Leave: A member is no longer interested in receiving traffic for that group and sends a leave message (IGMPv2 and MLDv1) or a membership report (IGMPv3 and MLDv2).
For IGMPv3 and MLDv2, a leave is a membership report with either an empty include list or a non-empty exclude list of sources that send packets to that multicast group.


  • Allow new source: A member adds new sources that send packets to a multicast group by sending a membership report.
If these sources are added in include mode, the member is interested in receiving packets from them and adds them to the include list. If these sources are added in exclude mode, the member deletes them from the exclude list. Source lists were introduced with IGMPv3 and MLDv2.


  • Block old source: A member blocks sources that send packets to a multicast group by sending a membership report.
If these sources are blocked in include mode, the member does not want receiving packets from them and deletes them from the include list. If these sources are blocked in exclude mode, the member adds them to the exclude list. Source lists were introduced with IGMPv3 and MLDv2.


  • Query: An IP multicast router queries the multicast reception state of neighbours with this message.
Active multicast members will reply to the membership query with a proper membership report. Queries may be general, for a specific group or for a specific group with a specific source list.


IGMPv1 supports membership queries and membership reports (joins). IGMPv2 and MLDv1 support membership queries, membership reports (joins) and leaves/dones. IGMPv3 and MLDv2 support membership queries and membership reports with source include and exclude lists.


Fast leave

Fast or immediate leave is a feature of the IP multicast router to allow reducing the amount of time to stop forwarding multicast traffic. When active, the router will track all members of all multicast groups of the neighbour interfaces and stop forwarding multicast traffic immediately as soon as the last member of an interface leaves the group. When not active, upon a leave of a member, the router will send a membership query and stop forwarding traffic if it doesn’t receive a proper membership report within a timeout. This feature only works starting with IGMPv2 and MLDv1.


Multicast IP address

A multicast IP address may be in the range between 224.0.0.0 and 239.255.255.255 (IPv4) or every address starting with ff00::/8 (IPv6).


Web interface


Overall multicast negotiations

The overall multicast activity graph shows all IGMP and MLD messages over time. As IGMPv3 and MLDv2 membership queries may contain a list of actions, this graph may show more messages than packets.

The PCAP button allows capturing all IGMP and MLD related traffic.


Groups

The group section shows all multicast groups.

  • Group IP: The IP address of the multicast group.
  • Last multicast negotiation: The last seen IGMP or MLD message related to that group.
  • Last traffic: The time of the last packet destinated to the multicast group. IGMP or MLD packets are excluded from the traffic.
  • Number of members: Number of unique members that sent IGMP or MLD messages related to that group.
This may be empty in case traffic for a multicast group has been seen, but no IGMP or MLD packets.
  • Graph: The history graph shows IGMP and MLD messages over time.
  • PCAP: The PCAP button allows capturing all IGMP and MLD messages related to that specific group.
By clicking on the IP address of the group or on the member count, a group specific statistics page is shown.


Overall multicast negotiations for group

The overall multicast activity graph shows all IGMP and MLD messages over time for that specific multicast group. The PCAP button allows capturing all IGMP and MLD messages related to that specific group.


Overall traffic for group

The overall traffic history graph shows all traffic for the specific multicast group. This graph may be useful to analyse fast leave support of the router. After the last leave for that group, the router should stop forwarding multicast traffic.


Group members

This list shows all member of the specific multicast group.

  • Member IP: The IP address of the member.
  • Protocol: The used protocol for multicast negotiations.
  • Last multicast negotiation: The last seen IGMP or MLD message related to that member.
  • Last join: The time of the join or allow new source of the current session.
As those messages are repeated by the member, only the time of the first occurence of that message belonging to a session is shown.
In case a new session starts, the leave time of an earlier session is not shown any longer.
  • Last join duration: The duration between the first join message and the first traffic for that multicast group address.
IGMP/MLD messages for that group are not counted as traffic. If there is no traffic for that group after the join and a leave, a - sign is shown.
  • Average join duration: The average of all join durations.
  • Last leave: The time of the leave or block old source of the last session.
As those messages are repeated by the member, only the time of the first occurrence of that message belonging to a session is shown.
  • Last leave duration: The duration between the first leave message and the last traffic for that multicast group. IGMP/MLD messages for that group are not counted as traffic.
If there is traffic for that multicast group, the duration is calculated and refreshed. After a timeout of 60 seconds, if there is still traffic, the measurement is stopped and a duration of >60 seconds is displayed. This is quite common for e.g. Multicast DNS (group 224.0.0.251 and ff02::fb) or time synchronisation services such as PTP with lots of members. If there is no traffic for that group after the leave att all, a - sign is displayed.
  • Average leave duration: The average of all leave durations.
  • Graph: The history graph shows IGMP and MLD messages over time.
  • PCAP: The PCAP button allows capturing all IGMP and MLD messages related to that specific member.