CCNP Practice Question: The default IGMP version on a Cisco IOS interface…

Answer analysis

Option-by-option breakdown

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

• ✗

  IGMPv1

  Why it's wrong here

  IGMPv1 cannot be the default on modern Cisco IOS interfaces because it lacks a Leave Group message, forcing the querier to rely on a slow Membership Query timeout (typically 130 seconds) before pruning a group. It also uses a fixed 2-second query interval and has no querier election mechanism, all of which were superseded by IGMPv2. Cisco's default is explicitly IGMPv2 unless an interface is manually overridden with the 'ip igmp version' command.

• ✓

  IGMPv2

  Why this is correct

  IGMPv2 is the correct default on Cisco IOS interfaces when multicast routing is enabled. It introduced the Leave Group message and a querier election mechanism, which makes group membership teardown much faster than IGMPv1, and these features are considered the baseline for IPv4 multicast on IOS. An interface with multicast routing (via a global 'ip multicast-routing' command) running IGMPv2 requires no additional version-specific configuration, so 'ip igmp version' is not present in the running config by default.

• ✗

  IGMPv3

  Why it's wrong here

  IGMPv3 is never the default in Cisco IOS because it is an opt-in feature designed for Source-Specific Multicast (SSM) and requires explicit configuration using the 'ip igmp version 3' command on the interface. Only hosts that need to signal source filtering (INCLUDE/EXCLUDE lists) would use v3, and legacy multicast receivers commonly rely on v2's simpler membership reporting. If v3 were the default, it would break backward compatibility with the vast installed base of v2 hosts, which is precisely why Cisco defaults to v2.

• ✗

  IGMPv2 is default only if PIM is enabled; otherwise, no IGMP.

  Why it's wrong here

  This statement is false because IGMPv2 is enabled by default on any interface participating in multicast routing, regardless of whether PIM is configured. The global command 'ip multicast-routing' activates multicast on all interfaces, and each interface then runs IGMPv2 as its host-tracking protocol; PIM only handles the multicast routing table and RPF checks, not the IGMP version. Disabling PIM or never configuring PIM does not change the IGMP version — IGMP remains active on the interface as long as multicast routing is enabled, so the default is still IGMPv2.