IP Network IconIP.network

IPv6 Solicited-Node

Compute the solicited-node multicast address from a unicast IPv6.

About This Tool

The IPv6 Solicited-Node Multicast Calculator generates the solicited-node multicast address for any IPv6 unicast address. Solicited-node multicast (ff02::1:ff00:0/104) is a critical component of IPv6 Neighbor Discovery Protocol (NDP), replacing ARP from IPv4. When a node needs to resolve an IPv6 address to a MAC address, it sends a Neighbor Solicitation to the target's solicited-node multicast address instead of broadcasting. This dramatically reduces network noise by ensuring only nodes with matching address suffixes process the request, making IPv6 neighbor discovery far more efficient than IPv4 ARP.

How to Use

  1. Enter any IPv6 unicast address (e.g., 2001:db8::1, fe80::1)
  2. The address can be in compressed or expanded format
  3. Click "Compute" to calculate the solicited-node multicast address
  4. View the result in both expanded format (all 128 bits shown)
  5. See the compressed format using :: notation
  6. The result always starts with ff02::1:ff and uses the last 24 bits of the input

Features

  • Calculates solicited-node multicast from any IPv6 unicast address
  • Generates ff02::1:ff00:0/104 prefix addresses
  • Shows both expanded and compressed formats
  • Accepts compressed or expanded IPv6 input
  • Validates IPv6 address format
  • RFC 4291 compliant calculation
  • Instant computation
  • Clear display of both output formats

Common Use Cases

  • Understanding IPv6 Neighbor Discovery Protocol (NDP)
  • Debugging IPv6 address resolution issues
  • Analyzing ICMPv6 Neighbor Solicitation packets
  • Configuring IPv6 multicast filters on switches
  • Learning how IPv6 replaces ARP broadcasts
  • Network troubleshooting and packet capture analysis
  • Understanding IPv6 link-local communication
  • Educational purposes: teaching IPv6 fundamentals
  • Validating NDP implementation correctness
  • Security analysis of IPv6 neighbor discovery

Technical Details

Solicited-node multicast addresses are computed by taking the last 24 bits of an IPv6 unicast address and appending them to the ff02::1:ff00:0/104 prefix. This creates a multicast group that a node must join for its own addresses.

Calculation Formula:

  • Prefix: ff02:0000:0000:0000:0000:0001:ff (104 bits fixed)
  • Suffix: Last 24 bits of the unicast address
  • Result: ff02::1:ffXX:XXXX where XX:XXXX are the last 24 bits

Examples:

  • 2001:db8::1 → ff02::1:ff00:0001 (last 24 bits: 00:0001)
  • 2001:db8::abcd:ef01 → ff02::1:ff0d:ef01 (last 24 bits: 0d:ef01)
  • fe80::20c:29ff:fe12:3456 → ff02::1:ff12:3456 (last 24 bits: 12:3456)

How NDP Uses Solicited-Node Multicast:

  1. Node A wants to communicate with 2001:db8::1
  2. A computes solicited-node address: ff02::1:ff00:0001
  3. A sends ICMPv6 Neighbor Solicitation to ff02::1:ff00:0001
  4. Only nodes with addresses ending in 00:0001 process the message
  5. Target node responds with Neighbor Advertisement
  6. A now knows the MAC address and can communicate

Efficiency Improvement Over ARP:

In IPv4, ARP uses broadcast (ff:ff:ff:ff:ff:ff) which forces every node on the link to process the request:

  • IPv4 ARP: Broadcast to ALL nodes on link
  • IPv6 NDP: Multicast to ~16 million possible addresses
  • With 2^24 = 16,777,216 possible solicited-node addresses, collision probability is low
  • Even when collisions occur, only a small subset processes the message
  • Dramatically reduces CPU interrupts on idle nodes

Multicast MAC Address:

The solicited-node IPv6 multicast address maps to an Ethernet multicast MAC:

  • Pattern: 33:33:XX:XX:XX:XX
  • Last 32 bits of IPv6 address map to last 32 bits of MAC
  • Example: ff02::1:ff00:0001 → MAC 33:33:ff:00:00:01
  • Ethernet NIC filters in hardware, further reducing CPU load

Required Multicast Group Membership:

Every IPv6 node must join the solicited-node multicast group for each of its unicast and anycast addresses. This is automatic and handled by the operating system's IPv6 stack.

Security Considerations:

  • Solicited-node multicast reduces but doesn't eliminate IPv6 address scanning
  • Attackers can still probe all 16 million solicited-node addresses
  • SEcure Neighbor Discovery (SEND, RFC 3971) can add cryptographic protection
  • Link-local scope (ff02) means messages don't cross routers