IPv4 Multicast
Table of Contents
IANA has a list of special addresses used by application for multicast purposes. The packets in this IP range are not forwarded by the routers. And thus these addresses are used for device and service discovery (like printers, …) in local network.
Address in the range 224.0.0.0 to 239.255.255.255 (inclusive) are multicast address.
Host Extensions for IP Multicasting [RFC1112] specifies the extensions required of a host implementation of the Internet Protocol (IP) to support multicasting. The multicast addresses are in the range 224.0.0.0 through 239.255.255.255. Address assignments are listed below.
The range of addresses between 224.0.0.0 and 224.0.0.255, inclusive, is reserved for the use of routing protocols and other low-level topology discovery or maintenance protocols, such as gateway discovery and group membership reporting. Multicast routers should not forward any multicast datagram with destination addresses in this range, regardless of its TTL.
1. Multicast DNS (mDNS)
mDNS packets use desitnation IP of 224.0.0.251 [RFC6762].
In computer networking, the multicast DNS (mDNS) protocol resolves hostnames to IP addresses within small networks that do not include a local name server.
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)
