CCNP Practice Question: The default multicast group range for…

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  224.0.0.0/4

  Why it's wrong here

  224.0.0.0/4 is the entire IPv4 multicast address space, spanning from 224.0.0.0 through 239.255.255.255. It includes link-local (224.0.0.0/24), globally scoped, GLOP, and administratively scoped ranges, so it is far too broad to be specific to Source-Specific Multicast. SSM is only a small subset of this space, namely the 232.0.0.0/8 range. Thus, while this is a multicast prefix, it does not uniquely identify or define the SSM address range.

• ✓

  232.0.0.0/8

  Why this is correct

  232.0.0.0/8 is the default and IANA-assigned range for Source-Specific Multicast (SSM), as defined in RFC 4607. In SSM, receivers explicitly subscribe to a specific source and group using the (S,G) notation, and this dedicated /8 prefix ensures that globally unique SSM groups are used consistently across the Internet. This range is the correct answer because it is exclusively reserved for SSM operations, unlike other multicast blocks that serve different purposes. Cisco devices and other routers recognize 232/8 as the default SSM range when SSM is enabled.

• ✗

  239.0.0.0/8

  Why it's wrong here

  239.0.0.0/8 is a special multicast range designated for administratively scoped (private) multicast as per RFC 2365. It is the multicast equivalent of IPv4 private addresses (e.g., 10.0.0.0/8), meant for internal use within a local network or organization, and packets in this range are typically not routed across the internet. This range is not used for Source-Specific Multicast; SSM uses the dedicated 232.0.0.0/8 range. Therefore, 239.0.0.0/8 is incorrect for SSM because it serves a completely different role in multicast addressing.

• ✗

  233.0.0.0/8

  Why it's wrong here

  233.0.0.0/8 is defined for GLOP addressing as per RFC 3180, where the middle two octets of the address encode the 16-bit autonomous system number of the organization that owns the address space. This allows each AS to have a set of globally unique multicast group addresses, but it is not related to Source-Specific Multicast. SSM relies on receiver-driven subscriptions to a specific source, not on statically allocated AS-based address blocks. Thus, 233.0.0.0/8 is incorrect for SSM because it is the GLOP range, not the SSM range.