Scope of multicast forwarding

• TTL-based scoping:

  • Each multicast router has a configured TTL threshold
  • It does not forward multicast datagram if TTL <= TTL-threshold
  • Useful at edges of a large intranet as a blanket parameter.

• Administrative scoping:

  • Use a portion of class D address space (239.0.0.0 thru 239.255.255.255)
  • Truly local to admin domain; address reuse possible.
  • In IPv6 scoping is an internal attribute of an an IPv6 multicast address

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