Static IP Post: 35989

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Special Forums IP Networking Static IP Post 35989 by Neo on Sunday 18th of May 2003 11:56:44 AM

05-18-2003

Administrator

Sorry, that is simply not true. We have a similar set up at home and use both DHCP and static addresses from the same address block. It works fine. Some PC get their addresses from the DHCP server (software in the Linksys router), others use assigned static IPs.

We don't do it, but the device can be configured to only allocate DHCP IPs from a small range of numbers. Unless you have a giant LAN that is using almost all the addresses, this is not a problem.

Since the poster indicated that they have a small LAN, simply assign a static IP outside of the 'normal' range of DHCP allocations.

And, if I'm not mistaken, ARP should make this moot in many DHCP servers; i.e. a good DHCP server should check its ARP cache before assiging an IP to check to see if it is in use on the segment.

For example, here is a quote from:

http://www.networkpenetration.com/dhcp_flaws.html

Quote:

Some DHCP servers issue ARP requests or ICMP pings to detect for IP addresses that may be reclaimed by the server. This is done as operating systems / interfaces do not release there assigned IP address when shutdown. Basic testing of the denial of service code successfully defeat the ARP method of reclaiming IP addresses (ICMP method was not tested) as the number and speed of requests for IP addresses was significantly higher than the number of ARP requests issued by the DHCP server (when running multiple copies of the source code in a script). The source code could be extended to sniff for ARP requests / ICMP ping requests and reply accordingly thus defeating the servers method of reclaiming addresses.

OBTW: if you are operating your own small private LAN, you don't need to be worried about the hypothetical DHCP vulnerability above.

Neo

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LEARN ABOUT DEBIAN

dhcp-helper

DHCP-HELPER(8)						      System Manager's Manual						    DHCP-HELPER(8)

NAME

       dhcp-helper - A DHCP/BOOTP relay agent.

SYNOPSIS

       dhcp-helper [OPTION]...

DESCRIPTION

       dhcp-helper is a DHCP and BOOTP relay agent. It listens for DHCP and BOOTP broadcasts on directly connected subnets and relays them to DHCP
       or BOOTP servers elsewhere. It also relays replies from the remote servers back to partially configured hosts. Once hosts are fully config-
       ured they can communicate directly with their servers and no longer need the services of a relay.

OPTIONS

       The only required option is at least one DHCP server to relay to. The simplest way to configure dhcp-helper on a router is just to give the
       interface to the network containing the DHCP server with a -b option. All the other interfaces present on the machine will then accept DHCP
       requests. On a machine which does not have an interface on the network containing the DHCP server, use a -s option instead.

       -s <server>
	      Specify  a  DHCP	or  BOOTP  server  to relay to. The server may be given as a machine name or dotted-quad IP address. More than one
	      server may be specified.

       -b <interface>
	      Relay to a DHCP or BOOTP server using broadcast via <interface>. This eliminates the need to give a server address.  <interface>	is
	      automatically added to the list of interfaces which will not receive DHCP requests.

       -i <interface>
	      Specify which local interfaces to listen on for DHCP/BOOTP broadcasts. If no -i flags are given all interfaces are used except those
	      specified by -e flags and those specified by -b flags.

       -e <interface>
	      Specify which local interfaces to exclude.

       -p     Use alternative ports (1067/1068) for the DHCP client and server.

       -v     Report the software release version and copyright information.

       -d     Debug mode, do not change UID, write a pid-file or go into the background.

       -r <file>
	      Specify an alternate path for dhcp-helper to record its process-id in. Normally /var/run/dhcp-helper.pid.

       -u <username>
	      Specify the userid to which dhcp-helper will change after startup. The daemon must normally be started as root,  but  it	will  drop
	      root  priviledges after startup by changing id to another user. Normally this user is "nobody" but that can be over-ridden with this
	      switch.

NOTES

       Dhcp-helper requires a 2.2 or later Linux kernel. The "Linux packet filter" and "packet socket" facilities are not required, which  is  the
       chief advantage of this software over the ISC DHCP relay daemon.

AUTHOR

       This manual page was written by Simon Kelley <simon@thekelleys.org.uk>.

																    DHCP-HELPER(8)

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