UDP port redirector
uredir is a small Linux daemon to redirect UDP connections. It can be
used to forward connections on small and embedded systems that do not
have (or want to use) iptables.
uredir can be used with the built-in inetd service in Finit to
listen for, e.g. SNMP connections, on some (safe) interfaces and forward
to an SNMP daemon on loopback.
- In normal mode it forwards packets to a given destination and remembers the sender's address. Packets received from the given destination are forwarded to the sender.
- In inetd mode
uredirlingers for three (3) seconds after forwarding a reply. This to prevent inetd from spawning new instances for multiple connections, e.g. an SNMP walk.
For a TCP port redirector, see redir.
uredir [-hinsv] [-I NAME] [-l LEVEL] [-t SEC] [SRC:PORT] DST:PORT -h Show this help text -i Run in inetd mode, get SRC:PORT from stdin, implies -n -I NAME Identity, tag syslog messages with NAME, default: uredir -l LVL Set log level: none, err, info, notice (default), debug -n Run in foreground, do not detach from controlling terminal -s Use syslog, even if running in foreground, default w/o -n -t SEC Timeout for connections, default 3 seconds -v Show program version Bug report address: https://github.com/troglobit/uredir/issues
This simple UDP proxy example forwards inbound DNS requests on any interface to an external DNS server on 192.168.0.1:
uredir :53 192.168.0.1:53
uredir from a process monitor like Finit or systemd, tell
it to not background itself and to only use the syslog for log messages:
uredir -ns :53 127.0.0.1:53
uredir in inetd mode, e.g. to redirect SNMP requests, try the
following. Runs in foreground, as required for inetd services, and uses
syslog for logging:
snmp dgram udp wait root uredir -i 127.0.0.1:16161
Build & Install
uredir is tailored for Linux systems and should build against any
(old) C libray. However,
uredir v3.0 and later require an external
library, libuEv. Installing it should present no surprises since it
too use a standard
configure script and support
latter is used by the
uredir build to locate the library and header
Hence, the regular
./configure && make is usually sufficient to build
uredir. But if libuEv is installed in non-standard location you
may need to provide the path:
PKG_CONFIG_PATH=/opt/lib/pkgconfig:/home/ian/lib/pkgconfig ./configure make
Origin & References
uredir was heavily inspired by redir(1), by Sam Creasey.