Updated Jul 2025
mDNS
mDNS stands for Multicast Domain Name System, which is a
form of domain name resolution.
mDNS is a variation of DNS service, which is a form
of domain name resolution. When an mDNS client
needs to resolve a hostname, it sends an IP multicast query message
that asks the host that has that name to identify itself.
An mDNS message is a multicast UDP packet sent using the following addressing:
- IPv4 address
224.0.0.251 or IPv6 address
ff02::fb
- UDP port
5353
- When using Ethernet frames
, the standard IP multicast MAC address
01:00:5E:00:00:FB (for IPv4
or 33:33:00:00:00:FB (for IPv6
If ipconfigUSE_DNS and ipconfigUSE_MDNS are set to 1 in FreeRTOSIPConfig.h then the FreeRTOS-Plus-TCP API function FreeRTOS_gethostbyname() can be used to resolve a text name to an IP address when the hostname has a postfix ".local".