IP Addressing and Subnets
Definition
On an IP network, every device has an IP address and a subnet mask. Together, these two values determine which devices it can communicate with directly. The mask splits the address into a network part and a host part. A /24 mask, written 255.255.255.0, assigns the first three numbers of the address to the network and the last one to individual hosts, giving 254 usable addresses. Two devices in the same subnet, for example 192.168.1.10 and 192.168.1.20 on a /24, can reach each other directly. If one of them is given an address in 192.168.2.x instead, direct communication becomes impossible, even when both are connected to the same cable, because each device concludes from the other's address that it is on a different network.
The guide
A device hands its traffic to the gateway, that is, to a router, only when it has determined that the destination is on a different subnet. A self-contained show network with no internet connection therefore often needs no gateway at all. A single consistent subnet is enough for every device to reach every other.
AV systems usually use the private address ranges reserved by RFC 1918: the 10.x, 172.16-to-31.x and 192.168.x blocks. A device that finds no DHCP server often assigns itself a link-local address in 169.254.0.0/16 (RFC 3927), outside those ranges; Dante devices do this by default, so an address beginning with 169.254 indicates that no DHCP server was found. One of the most common network faults is also one of the least visible: a device with a wrong IP address or mask, physically connected and showing a link light, yet completely isolated from the rest of the system.
The rule
Two devices communicate directly only when they belong to the same subnet.
Glossary terms
Sources
- IETF RFC 1918 (1996) §3, trois plages privées : 10/8, 172.16/12, 192.168/16 · datatracker.ietf.org
- IETF RFC 4632 (2006) §3.1 : notation CIDR, /24 = 24 bits de préfixe · datatracker.ietf.org
- IETF RFC 950 (1985) : valeurs d'hôte tout à 0 et tout à 1 réservées, d'où 2ⁿ − 2 adresses · datatracker.ietf.org
- IETF RFC 1122 (1989) §3.3.1 : décision local ou distant, passerelle de premier saut · datatracker.ietf.org
- IETF RFC 3927 (2005) : adresses de lien local 169.254/16 auto-attribuées sans DHCP · datatracker.ietf.org
- Audinate : dépannage de l'adressage IP Dante · dev.audinate.com