LLMNR

LLMNR stands for Link Local Multicast Name Resolution, which is a protocol for name resolution.

LLMNR is a multicast protocol used on local area networks. It is the method used by all major web browsers to resolve names that do not include a dot ('.'). For example, if you attempt to open the web page: http://my_freertos_device/index.html, then the web browser would send an LLMNR request to try and resolve the name 'my_freertos_device'.

All LLMNR packets are sent to IP address 224.0.0.252 on MAC address 01:00:5E:00:00:FC, so the network interface (MAC) must be programmed to accept packets on that address for LLMNR to function. In addition ipconfigUSE_LLMNR must be defined as 1 in FreeRTOSIPConfig.h, and the user must provide the implementation of a callback function xApplicationDNSQueryHook() that takes a char pointer as a parameter and returns pdTRUE if the name passed into the function matches a name used to identify the node.

Useful links:

• TCP/IP Networking Basics
• FreeRTOS+TCP networking tutorial

Other networking basics pages:

• Ethernet Networking and Addressing
• MTU - Maximum Transmission Unit
• IP Networking
• IP Network Addressing
• ARP - Address Resolution Protocol
• Subnets / Netmasks
• Gateways and Routers
• UDP Networking
• TCP Networking
• MSS - Maximum Segment Size
• Port Numbers
• Sockets
• Binding
• Clients and Servers
• Static IP Addresses
• DHCP - Dynamic Host Control Protocol
• Name Resolution
• DNS - Domain Name Service
• LLMNR - Link-local Multicast Name Resolution
• NBNS - NetBIOS Name Service
• Bytes Order and Endian