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4. IGMP Questionnaire

As part of this work, the following questions were asked on the MAGMA discussion list and were sent to known switch vendors implementing IGMP snooping. The individual contributions have been anonymized upon request and do not necessarily apply to all of the vendors' products.

The questions were:

  • Q1: Do your switches perform IGMP Join aggregation? In other words, are IGMP joins intercepted, absorbed by the hardware/software so that only one Join is forwarded to the querier?
  • Q2: Is multicast forwarding based on MAC addresses? Would datagrams addressed to multicast IP addresses 224.1.2.3 and 239.129.2.3 be forwarded on the same ports-groups?
  • Q3: Is it possible to forward multicast datagrams based on IP addresses (not routed)? In other words, could 224.1.2.3 and 239.129.2.3 be forwarded on different port-groups with unaltered TTL?
  • Q4: Are multicast datagrams within the range 224.0.0.1 to 224.0.0.255 forwarded on all ports whether or not IGMP Joins have been sent?
  • Q5: Are multicast frames within the MAC address range 01:00:5E:00:00:01 to 01:00:5E:00:00:FF forwarded on all ports whether or not IGMP joins have been sent?
  • Q6: Does your switch support forwarding to ports on which IP multicast routers are attached in addition to the ports where IGMP Joins have been received?
  • Q7: Is your IGMP snooping functionality fully implemented in hardware?
  • Q8: Is your IGMP snooping functionality partly software implemented?
  • Q9: Can topology changes (for example spanning tree configuration changes) be detected by the IGMP snooping functionality so that for example new queries can be sent or tables can be updated to ensure robustness?

The answers were:

      ---------------------------+-----------------------+
                                 |     Switch Vendor     |
      ---------------------------+---+---+---+---+---+---+
                                 | 1 | 2 | 3 | 4 | 5 | 6 |
      ---------------------------+---+---+---+---+---+---+
      Q1 Join aggregation        | x | x | x |   | x | x |
      Q2 Layer-2 forwarding      | x | x | x | x |(1)|   |
      Q3 Layer-3 forwarding      |(1)|   |(1)|   |(1)| x |
      Q4 224.0.0.X aware         |(1)| x |(1)|(2)| x | x |
      Q5 01:00:5e:00:00:XX aware | x | x | x |(2)| x | x |
      Q6 Mcast router list       | x | x | x | x | x | x |
      Q7 Hardware implemented    |   |   |   |   |   |   |
      Q8 Software assisted       | x | x | x | x | x | x |
      Q9 Topology change aware   | x | x | x | x |   |(2)|
      ---------------------------+---+---+---+---+---+---+
                x  Means that the answer was Yes.
  (1) In some products (typically high-end) Yes; in others No.
  (2) Not at the time that the questionnaire was received
      but expected in the near future.