dhcp-fwd(1)

NAME

dhcp-fwd - starts the DHCP forwarding agent

SYNOPSIS
dhcp-fwd [-n] [-d] [-v] [-h] [-c config_file]

DESCRIPTION
dhcp-fwd starts a DHCP forwarding agents which relays DHCP messages between subnets with different sublayer broadcast domains.

When called without arguments, it reads its configuration from /etc/dhcp-fwd.cfg and forks itself into background. An alternative configfile can be given by the -c option; the forking can be prevented with the -n switch. There exists a -d option which is indented for debugging purposes and prevents forking too. Currently it is just an alias for -n.

Although the program must be started as root, it will drop its privileges and go into a chroot-jail after finishing the initialization.

OPTIONS

-n  Prevents daemon from going into background after initialization. This option may be useful when using advanced init-concepts like minit (http://www.fefe.de/minit/).

-d  Turns on debugging mode and prevents forking; currently it is just an alias for -n.

-c  config_file
    Specifies the configfile to use; the default is /etc/dhcp-fwd.cfg.

-v  Shows version

-h  Shows help

CONFIGURATION FILE
The default location of the configfile is determined at compilation-time and can be overridden by using the -c option. When an option needs a boolean parameter, the keywords true, false, 0, 1, yes and no are possible values.

Within the configfile the following options MUST be set:

user username|uid
    The program setuid()'s to the given user after finishing its initialization. The parameter must be an alphanumeric username or a numeric uid.

group groupname|gid
    The program setgid()'s to the given group after finishing its initialization. The parameter must be an alphanumeric groupname or a numeric gid.

chroot path
    The program goes into this directory and calls there chroot() after finishing its initialization.

pidfile filename
    The file where the pid of the daemon will be written into.

Beside the mandatory options above, the following options are possible:

ulimit resource limit
    Sets a maximum limit for the given resource by calling setrlimit() appropriately. Possible values for resource are stack, data, core, rss, nproc, nofile, memlock, as and (if supported by your OS) locks. For the meaning of this values see setrlimit(2).

    limit may be plain unsigned number, a number followed by 'k' (*1000), 'K' (*1024), 'm' (*1000k), 'M' (*1024K) or '-1' to remove the limit for this resource.

logfile filename
    Specifies the file where messages will be stored. This file is located relatively to the directory where dhcp-fwd was started and not to the directory given at the chroot option.

if ifname has_clients has_servers allow_bcast
    Declares an interface and sets parameter of the network topology. When an interfacename is used in one of the other options, it must have been declared by if already.

    ifname is the name of the interface as being used e.g. by ifconfig also (e.g. eth0).

    has_clients and has_servers tell if messages from clients or servers can be expected on this interface. BOOTREQUESTs are assumed to be client- and BOOTREPLYs are assumed to be server-messages. Unexpected packages will be dropped away.

    allow_bcast is/was an experimentell features and will be disappear probably. When not set, the interface will not send packages to IP-broadcast addresses. This affects messages to clients only; when specifying a bcast-server, this option will be ignored.

name ifname agent-id
    specifies the RFC 3046 agent-id for the given interface. When not used explicitly, the interfacename will be assumed as the agent-id.

ip ifname ip
    assigns the ip to be used in the giaddr field. By default to IP of the interface will be assumed but when having multiple IPs for one interface this option may be usefully.

    Attention: This IP will not be used in the IP-layer; this means that the UDP packet sent to the server will contain the IP assigned by the system. To setup this address, usual SNAT rulesets in a local packetfilter are recommended.

server type info
    Defines the DHCP server to be used. The following types are supported:

    server ip address [interface]
        address is a dotted IP-address and the optional interface the name of an interface. Please note that mixing declarations without an interface parameter and such ones with this parameter will fail.

    server bcast interface
        the DHCP server with be assumed at interface interface and contacted with broadcast messages.

For an example see the contrib/dhcp-fwd.conf file in the source-tarball.

FILES

/etc/dhcp-fwd.conf
    configuration file

/usr/sbin/dhcp-fwd
    executable

SEE ALSO
RFC 2131, 2132, 3046

AUTHOR
Enrico Scholz <enrico.scholz@informatik.tu-chemnitz.de>