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RARPD(1) 1 (rarpd-dx user's manual) RARPD(1)

NAME

rarpd — answer Reverse-ARP REQUESTs

SYNOPSIS

rarpd [-AadevV] [-b bootdir] [-l logfile] [-E ethers] interface

DESCRIPTION

rarpd listens for RARP requests broadcast by clients. If the MAC address of the client is found in ethers(5) and the obtained hostname is resolvable to a valid IP address from the attached network, rarpd answers to the client with a RARP reply and provides an IP address.

Warning

This facility is deeply obsoleted by BOOTP and later DHCP protocols. However, some clients actually still need this to boot.

OPTIONS

, --all
Listen on all available interfaces. Currently it is an integral option, its function is overwritten with the interface argument. It should not be used.
, --arp
Accept and respond to incoming requests using the ARP ethertype (0x0806) in addition to the usual RARP ethertype (0x8035). In all other respects the protocol handling is identical—RARP uses the exact same packet format as ARP but with distinct opcodes. This is allegedly required by some rare clients.
, --verbose
Be verbose.
, --foreground
Do not go to background.
, --ethers file
Read ethers(5) entries from the specified file to resolve MAC addresses to hostnames instead of querying the system database.
, --no-check-tftpboot
Do not check for the presence of a boot image before replying.
, --check-tftpboot bootdir
Check the existence of boot images in the directory bootdir; see Boot Images below for more details. The default is /tftpboot.
, --log-file target
Output diagnostic messages to the specified target.

If target is the special value syslog, then log messages are written via the POSIX () interface. This is the default on systems which support this functionality.

If target is the special value stderr, then log messages are written to the standard error stream. This is the default on systems which do not support ().

Otherwise, target is the name of a file to which rarpd will append log messages.

, --allow-offlink
If there is no matching IP address for the network of the receiving interface, but we do have some IP address for the requestor, possibly for a different network, then reply using that address. By default, no reply is sent if there is no match for the receiving interface.
, --version
Print a version message to standard output and then exit.
, --help
Print a help message to standard output and then exit.

OPERATION

Signals

Upon receipt of this signal, rarpd will close and reopen the log file (if this feature in use), invalidate all cached network information, and rescan addresses on network interfaces.

Boot Images

To allow multiple boot servers on the network rarpd optionally checks if a Sun-like bootable image is present. This behaviour can be controlled by the --[no-]check-tftpboot options.

It is typically formatted as Hexadecimal_IP.ARCH or just Hexadecimal_IP. For example, to load sparc 193.233.7.98, C1E90762.SUN4M is linked to an image appropriate for SUN4M in the specified directory. rarpd will check for any file which begins with Hexadecimal_IP and reply only if such a file exists.

Security

rarpd requires CAP_NET_RAW capability to listen and send RARP and ARP packets. It also needs CAP_NET_ADMIN to assist the kernel with ARP resolution; this is not strictly required, but some (to be more exact: most) of the clients are so badly broken that they are not able to answer to ARP before they are fully booted. This is no surprise, taking into account that clients using rarpd in 2002 are all unsupported relic creatures of the 1990s and even earlier.

AUTHORS

rarpd was originally written by Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>, and was previously maintained as part of the Linux iputils package.

This rarpd-dx package incorporates various improvements by Nick Bowler <nbowler@draconx.ca>.

SEE ALSO

nsswitch.conf(5), ethers(5), tftpd(8).

STANDARDS

R. Finlayson, T. Mann, J.C. Mogul, M. Theimer, A Reverse Address Resolution Protocol, IETF STD 38, RFC 903 (June 1984) doi:10.17487/RFC903

September 4, 2026 rarpd