NETROM(4)

✨ NETROM(4) — the AF_NETROM glow-up ✨

okay so bestie, welcome to the Linux Programmer's Manual corner where we're talking about AF_NETROM, aka the NET/ROM amateur packet radio protocol family. it's giving "niche but iconic" and i'm obsessed. 🎀

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NAME

AF_NETROM — the NET/ROM amateur packet radio protocol family. yes, that's the whole name, and yes, it ate. 💅

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DESCRIPTION

NET/ROM is a protocol used extensively by radio amateurs. the Linux NET/ROM protocol family lets you access these protocols via the standard networking socket metaphor — so if you know sockets, you're already lowkey home. 🏠✨

the NET/ROM protocol layer only supports connected mode. periodt. but plot twist: IP traffic may be stacked on top of NET/ROM frames using a non-standard extension to the NET/ROM protocol. no cap, that's a thing. 🌈

the only mode of operation is connected mode, which is the mode used for a socket of type SOCK_SEQPACKET (stream sockets are not available in NET/ROM — rip to that vibe 💀). this means you (yes, you, the user) have to ensure that:

• output data is suitably packetised 📦
• input data is read a packet at a time into a buffer of suitable size

basically, it's on you to keep things tidy, bestie. main character responsibility fr fr. 🫶

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addresses, but make it cute

NET/ROM addresses consist of 6 ascii characters and a number called the SSID. these are encoded into a sockaddr_ax25 structure which is provided to the relevant system calls. iykyk. 🦋

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the unusual properties era

NET/ROM has some unusual properties. notably, in a multi-user system an AX.25 address is often associated with a user, and some users may not have such an association. a set of ioctl calls are provided to manage an association table. so yeah, it's giving "extra admin but we handle it". 😭

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socket options for SOL_NETROM

NET/ROM supports the following socket options for SOL_NETROM. let's go through them one by one because we're thorough like that ✨:

• NETROM_T1 — the T1 timer, measured in 1/10ths of a second ⏱️
• NETROM_T2 — the T2 timer, also in 1/10ths of a second ⏱️
• NETROM_N2 — the retry counter, and yes it's configurable too 🎛️

⚠️ important caveat bestie: there is no 'infinite retry' option supported however. so don't come looking for it, it's not invited to the party. 🙈

it's also possible for an application to request that the NET/ROM layer return the NET/ROM header as well as the application data — this is done via the NETROM_HDRINCL socket option. iconic behavior honestly. 👑

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SEE ALSO

like, go read these too, they're all part of the lore 📚:

• call(1)
• socket(2)
• setsockopt(2)
• getsockopt(2)
• nrbroadcast(5)
• nrports(5)
• netromd(8)
• noderest(8)
• nodesave(8)
• nrparms(8)

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AUTHOR

shoutout to Jonathan Naylor G4KLX <g4klx@g4klx.demon.co.uk> for writing this — absolute legend behavior, we stan 🫡💖

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and that's the tea, bestie 🍓 this page is from the Linux manual, version dated 15 July 2011, and it's giving vintage but still valid. now go forth and packet-radio responsibly 💅✨🎀