Control-plane multicast in IPv6 — which multicast group does EIGRP for IPv6 (EIGRPv6) use for neighbor discovery and updates?

Introduction / Context:
IPv6 routing protocols use specific link-local multicast groups to discover neighbors and exchange control information efficiently on a segment. Knowing the correct multicast addresses helps engineers interpret packet captures and verify control-plane health using tools like debug and show commands.

Given Data / Assumptions:

• We are concerned with EIGRP for IPv6 (often written EIGRPv6).
• We are considering link-local scope multicast addresses (FF02::/16).
• No authentication or special transport changes are assumed.

Concept / Approach:
EIGRPv6 uses the all-EIGRP-routers IPv6 multicast address FF02::A for neighbor discovery and control updates. Other common addresses include FF02::5 (all OSPF routers), FF02::6 (all OSPF designated routers), and FF02::9 (RIPng). FF02::1 is the all-nodes address and is not used for routing protocol control traffic.

Step-by-Step Solution:
Identify the protocol in question: EIGRP for IPv6.Recall the standard control multicast address mapping.Select FF02::A as the EIGRPv6 group for neighbor and update traffic.

Verification / Alternative check:
Packet captures on an EIGRPv6-enabled interface show EIGRP packets to destination FF02::A. show ipv6 eigrp interfaces can also confirm active operation on links using that multicast address.

Why Other Options Are Wrong:

• B: FF02::9 is used by RIPng.
• C/D: FF02::5 and FF02::6 are used by OSPFv3 (all routers and all DRs respectively).
• E: FF02::1 is the all-nodes address; using it for routing updates would be inefficient and noisy.

Common Pitfalls:
Mixing OSPFv3 and EIGRPv6 groups or assuming the same values as in IPv4 where multicast addresses differ.

Final Answer:
FF02::A