mDNS Reflector

mDNS Reflector (mdns-reflector) is a lightweight and performant multicast DNS (mDNS) reflector with a modern design. It reflects mDNS queries and responses among multiple LANs, which allows you to run untrusted IoT devices in a separate LAN but those devices can still be discovered in other LANs.

Highlights

• Low footprint, no dynamic memory allocation during reflecting
• Rootless - can be run as either root or non-root
• Supports zone based reflection
• Supports both IPv4 and IPv6
• Leverages epoll on Linux and kqueue on BSD and macOS

It provides a command line interface (CLI) familiar to the discontinued mdns-repeater.

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Installation of mDNS Reflector using prebuilt binaries

Docker

docker pull yuxzhu/mdns-reflector:latest

Podman

podman pull yuxzhu/mdns-reflector:latest

Fedora / CentOS 8 / CentOS Stream 8

dnf copr enable -y yux/networking
dnf install -y mdns-reflector

CentOS 7

curl -fLo /etc/yum.repos.d/yux-networking-epel-7.repo  https://copr.fedorainfracloud.org/coprs/yux/networking/repo/epel-7/yux-networking-epel-7.repo
yum install -y mdns-reflector

Debian / Ubuntu

Available in Debian 'experimental' branch:

• https://packages.debian.org/experimental/mdns-reflector

It can happen that the version in experimental is outdated. In that case experienced users can either build the .deb package themselves

• by using this the Debian Salsa repo: https://salsa.debian.org/debian-edu-pkg-team/mdns-reflector
• by using the included debian/ folder.

OpenWRT

Coming soon.

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Installing mDNS Reflector from Source

git clone https://github.com/vfreex/mdns-reflector
cd mdns-reflector && mkdir build && cd build
cmake -DCMAKE_BUILD_TYPE=release ..
make install

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Usage

mdns-reflector is easy to use. Just run the following command on a multi-homed host:

mdns-reflector -fn eth0 eth1

where eth0 and eth1 are the interfaces that you want to reflect mDNS for.

Run mdns-reflector -h for help.

Similarly, run with Docker in the foreground:

docker run --net=host yuxzhu/mdns-reflector:latest mdns-reflector -fn eth0 eth1

Or run with Docker as a daemon:

docker run -d --restart=always --net=host yuxzhu/mdns-reflector:latest mdns-reflector -fn eth0 eth1

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Systemd service

You can enable the systemd service with:

systemctl enable --now mdns-reflector

The main configuration file for the service daemon is located at: /etc/mdns-reflector/mdns-reflector.conf

Although you can add files to /etc/mdns-reflector/conf.d/ to overwrite the main configuration file.

Quick Tip: Adding a number and an underscore like 10_ as a prefix to your filename is good practice and ensures a predictable priority of the config files. 99_* files have a higher priority than 00_* files which means that the settings in file 20_example.conf would overwrite settings from 10_example.conf.

Multiple systemd services

mDNS Reflector supports multiple services running in parallel. You can achieve this by creating files like /etc/mdns-reflector/%i.conf.

Now enable the systemd service with this specific config file:

systemctl enable --now mdns-reflector@$(systemd-escape "%i")

NOTE: Replace %i with your config filename without the .conf at the end. The .conf filename suffix is still necessary though.

Important information about multiple services running in parallel

Let us define a few networks to make an example frame <iface_name>: <network_name>:

• eth_home: Homenetwork
• eth_smart: Smarthome-Devices
• eth_print: Printers

We want the devices in Printers to announce their services into the Homenetwork. Likewise the devices in Smarthome-Devices should also announce their services into the Homenetwork.

mDNS Reflector does not support an interface occuring in more than one reflection planes. For example:

mdns-reflector eth_home eth_smart -- eth_home eth_print # Wrong!

At the moment this is only possible if multiple mDNS Reflector services are running in parallel.

Uni-directional service announcement is not supported at the moment but is planned.

So, for this example you'll need two config files.

/etc/mdns-reflector/smarthomestuff.conf:

INTERFACES="eth_home eth_smart"
More stuff...

/etc/mdns-reflector/printerstuff.conf:

INTERFACES="eth_home eth_print"
More stuff...

Enabling the service of course:

systemctl enable --now mdns-reflector@$(systemd-escape "smarthomestuff")
systemctl enable --now mdns-reflector@$(systemd-escape "printerstuff")

This would make all mDNS services visible in Homenetwork. But beware this also makes all services from devices within the Homenetwork visible to the Smarthome-Devices and Printers networks.

Services within the Smarthome-Devices network won't be announced to the Printers network and vice-versa.

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License

Copyright (C) 2021-2023 Yuxiang Zhu me@yux.im

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see https://www.gnu.org/licenses/.