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300-410 Practice Question: According to RFC 2460, what is the correct…
According to RFC 2460, what is the correct behavior when an IPv6 router receives a packet with a source address that is a multicast address?
⚠ Common exam trap
It's easy for candidates to confuse multicast source address rules with broadcast or unicast reverse path forwarding (uRPF) checks, assuming an ICMP error is sent or that the packet is forwarded normally.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The router drops the packet silently.
RFC 2460 specifies that an IPv6 router must silently drop any packet with a multicast source address, as multicast addresses are only valid as destination addresses. This behavior prevents loops and misuse of multicast addressing in the network layer.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The router forwards the packet normally.
Why it's wrong here
IPv6 does not allow multicast source addresses.
- ✓
The router drops the packet silently.
Why this is correct
Per RFC 2460, a packet with a multicast source address is invalid and must be discarded.
- ✗
The router sends an ICMPv6 error message back to the source.
Why it's wrong here
No ICMP error is generated for invalid source addresses; the packet is simply dropped.
- ✗
The router rewrites the source address to the link-local address of the interface.
Why it's wrong here
Routers do not modify source addresses; they drop invalid packets.
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.