Tiny mDNS Announcer

tiny-mdns-ann is a lightweight shell utility to announce device's .local hostname and network services via mDNS.
Hostname can then be resolved by any machine supporting mDNS/Avahi LAN discovery.

tiny-mdns-ann only depends on netcat, as found in busybox, or other standalone implementations.
It merely sends unsolicited UDP announcement packets, and does not answer queries.
It is a best-effort lightweight announcer, and is not intended as a replacement for fully compliant mDNS responder.

Features:

• hostname LAN IP address resolution
• optionally advertises http and ssh services
• IPv4 and IPv6 support
• OpenRC and Systemd services

Benefits:

• extremely small footprint
• runs under POSIX shell
• compatible with busybox's nc
• leverages socat if available, for more robust announcements

Setup procedure:

Make script executable and run tiny-mdns-ann on device as follows:

usage: tiny-mdns-ann [OPTIONS]

Announce HOSTNAME.local over mDNS on active interfaces.

Options:
  --help                Show this help.
  --host NAME           Host name to announce in the .local domain.
  --http[=PORT[,PATH]]  Advertise HTTP, default port 80, path /.
  --ssh[=PORT]          Advertise SSH, default port 22.

Environment:
  INTERVAL              Announcement interval in seconds, default 60.
  ADVERTISE_IPV6        Enable IPv6 announcements, default 1.
  DEBUG_LOG             Log each announcement, default 0.

Main execution steps are logged: grep tiny-mdns-ann /var/log/messages.

OpenRC and Systemd services files are provided to run tiny-mdns-ann as a boot service.
A complete Alpine Linux package is also in the works.

Note & limitations:

• As nc does not allow multicast ttl/hop-limit controls, announcements do not set mDNS-required value of 255, but work just fine in most cases.
• If socat is available, it is used in place of nc to send announcements with ttl/hop-limit 255.
• hosts with advanced networking routing setup or firewall may need to adapt settings to let mdns port 5353 free for sending announcements.