Link-Local Multicast Name Resolution

The Link Local Multicast Name Resolution (or LLMNR) is a protocol based on the Domain Name System (DNS) packet format that allows both IPv4 and IPv6 hosts to perform name resolution for hosts on the same local link.

Packet 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.

External links

• TechNet Link-Local Multicast Name Resolution

RFCs

• RFC 4795, Informational, RTP Profile for Audio and Video Conferences with Minimal Control