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Forwards DHCP messages between subnets
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ensc/dhcp-fwd
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Release notes for dhcp-forwarder, version 0.4 ============================================= This program is used to forward DHCP and BOOTP messages between two networks with different broadcast domains. FEATURES ======== - runs as non-root in a chroot-environment - uses AF_INET sockets to listen for DHCP messages. Thus, packetfilters like iptables can be used to filter incoming messages - supports DHCP agent IDs as described in RFC 3046. These IDs can be defined freely. - small memory-footprint: | $ ./dhcp-fwd -v; ls -l dhcp-fwd; file dhcp-fwd | dhcp-forwarder 0.3.3 | -rwxrwxr-x 1 ensc ensc 29368 Aug 29 15:59 dhcp-fwd | dhcp-fwd: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), statically linked, stripped | # ps hu `pidof dhcp-fwd` | dhcp-fwd 3227 0.0 0.1 64 64 ? S 15:58 0:00 ./dhcp-fwd -c etc/dhcp-fwd.cfg These numbers are the result of: | $ ./configure --enable-release --enable-dietlibc --disable-logging | $ make DIET='diet -Os' && strip dhcp-fwd ## dietlibc-0.20, gcc-3.2 INSTALLATION ============ - build with the usual './configure && make && make install'. When not having an actual dietlibc, you will need to call ./configure with a '--disable-dietlibc' option. *NOT* using this flag results in significantly smaller binaries and memory consumption. Old dietlibc versions (<0.17) are causing strange warnings while compiling and I am not not sure if they are harmful or not. I am running dhcp-fwd with dietlibc-0.17 successfully. - create an user the daemon will setuid() to. Do not use 'nobody'; it makes no sense to have running all important services as the 'nobody' user... - create a directory where the daemon will chroot to. This directory should be created in the most secure manner; the daemon does not access this directory so I suggest to make it unreadable, unwritable and unaccessible for the user created before - install contrib/dhcp-fwd.conf in $(sysconfdir)/ and adapt it to your needs; the possible settings are described in this file. An alternative cfg-file can be given on the commandline with the '-c' option. - start '$(sbindir)/dhcp-fwd' If you are a RH 7.3 user, I suggest to build an RPM with | rpm -tb dhcp-forwarder-0.1.tar.bz2 --without dietlibc' and install the resulting binary. The '--without dietlibc' is neccessary since RH ships an elder dietlibc. After installation, the daemon can be started with | service dhcp-fwd start and enabled permanently with | chkconfig dhcp-fwd on BUGS ==== - bad behavior when serverside-interface has a smaller MTU than the MTU on the server itself. An example is [Server]-- Ethernet --[Router]-- PPP --[Forwarder] (example is not completely correct since the program assumes an MTU of 1500 or greater; but when server is on a special device (IPSec VLAN??) a similar situation can occur) - on client-side only ethernet supported; same holds on server-side if server is a broadcast-address - works with Linux only; the device-binding stuff is not specified by SUSv3 and I do not know enough about other systems to provide a better solution - it does not set the agent-id on large DHCP-messages although it would be possible to enlarge the package or to use the bootfile/sname header-fields - untested; particularly, I would like to get feedback about success or failures in the following areas: * cooperation within an IPv6 network or * running on a big-endian host (will probably fail) * IP fragmentation SAMPLE CONFIGURATIONS ===================== The contributed configfile contrib/dhcp-fwd.conf contains a sample configuration for the real-world scenario described in its header: -------------- ---------- ------------- | DHCP Server | | | | | | 192.168.8.66 |------<eth1>| dhcp-fwd |<eth2>------| Clients | | | | | | | -------------- ---------- ------------- Additionally it has been tested successfully when running in the following environment: -------------- ---------- ------------- | DHCP Server | | | | | | 192.168.8.66 |------<eth1>| Firewall |<eth2>------| Clients | | | | | | | -------------- ---------- | ~~~~~~ | | |dhcp- | | | | fwd | | | ~~~~~~ | ------------- The clients have a netmask of 192.168.0.0/255.255.248.0; the dhcp-fwd itself has one interface with an IP of 192.168.0.6. Then I am using the following core-configuration: | if eth0 true true true | name eth0 ws-c | server ip 192.168.8.66
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