Link-Local Multicast Name Resolution

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Protocol details

In responding to queries, responders listen on UDP port 5355 on the following link-scope Multicast address:

• IPv4 - 224.0.0.252, MAC address 01-00-5E-00-00-FC
• IPv6 - FF02:0:0:0:0:0:1:3 (this notation can be abbreviated as FF02::1:3), MAC address 33-33-00-01-00-03

The responders also listen on TCP port 5355 on the unicast address that the host uses to respond to queries.

Packet header structure

Bit offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 ID 16 QR Opcode C TC T Z Z Z Z RCODE 32 QDCOUNT 48 ANCOUNT 64 NSCOUNT 80 ARCOUNT

• ID - A 16-bit identifier assigned by the program that generates any kind of query.
• QR - Query/Response.
• OPCODE - A 4-bit field that specifies the kind of query in this message. This value is set by the originator of a query and copied into the response. This specification defines the behavior of standard queries and responses (opcode value of zero). Future specifications may define the use of other opcodes with LLMNR.
• C - Conflict.
• TC - TrunCation.
• T - Tentative.
• Z - Reserved for future use.
• RCODE - Response code.
• QDCOUNT - An unsigned 16-bit integer specifying the number of entries in the question section.
• ANCOUNT - An unsigned 16-bit integer specifying the number of resource records in the answer section.
• NSCOUNT - An unsigned 16-bit integer specifying the number of name server resource records in the authority records section.
• ARCOUNT - An unsigned 16-bit integer specifying the number of resource records in the additional records section.

See also

• Network Basic Input/Output S

External links

• Link-Local Multicast Name Resolution, Microsoft TechNet
• RFC 4795, Informational, Link-Local Multicast Name Resolution (LLMNR)
• LLMNR, Multicast DNS and names on your LAN