Host Extensions for IP Multicasting

Deering

network routing multicast

@misc{deering:ietf-1989,
  author={S. E. Deering},
  title={Host Extensions for {IP} Multicasting},
  series={Request for Comments},
  number={1112},
  howpublished={{RFC} 1112 (Proposed Standard)},
  publisher={IETF},
  organization={Internet Engineering Task Force},
  year={1989},
  month={August},
  url={\url{http://www.ietf.org/rfc/rfc1112.txt}},
  note={Updated by RFC 2236}
}

Host Extensions for IP Multicasting. Deering. RFC 1112

• Coordination and forwarding between routers is not addressed in this RFC, just host requirements.
• Multicast groups are identified by Class D IP addresses, those with 1110 as their high order bits
  • This ranges from 224.0.0.0 to 239.255.255.255
  • 224.0.0.0 is guaranteed to not be assigned
  • 224.0.0.1 is assigned to all IP hosts, including gateways
• pg 3, interesting figure, note placement of IP-to-local mapping:

         |                                                          |
         |              Upper-Layer Protocol Modules                |
         |__________________________________________________________|

      --------------------- IP Service Interface -----------------------
          __________________________________________________________
         |                            |              |              |
         |                            |     ICMP     |     IGMP     |
         |             IP             |______________|______________|
         |           Module                                         |
         |                                                          |
         |__________________________________________________________|

      ---------------- Local Network Service Interface -----------------
          __________________________________________________________
         |                            |                             |
         |           Local            | IP-to-local address mapping |
         |          Network           |         (e.g., ARP)         |
         |          Modules           |_____________________________|
         |      (e.g., Ethernet)                                    |
         |                                                          |

• Multicast datagrams sent using same "Send IP" operation as unicast
  • Desirable but not necessary extensions for sending: Multicast TTL, identification of interface to use, inhibit local delivery of datagram
  • Must recognize group IP addresses and route out interfaces appropriately
• "The IP source address of the outgoing datagram must be one of the individual addresses corresponding to the outgoing interface."
  • And it only goes out one interface
• To receive, must provide join & leave group functions
• Host components of IGMP version 1:
  • Routers issue Host Membership Query messages to the all-hosts group
  • For each group it belongs to, the host sets a timer for a random interval; when that timer expires, it issues a Host Membership Report for that group
  • Membership reports are addressed to the group being reported; if a host overhears a membership report for one of its groups, it kills that timer and squelches its own report
  • Hosts also generate membership reports upon joining a group (actually, one, two, or more reports, in case some are dropped)
  • This is clearly all messier on a MANET