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 CENTOS

dhcp_release

DHCP_RELEASE(1) 					      General Commands Manual						   DHCP_RELEASE(1)

NAME

       dhcp_release - Release a DHCP lease on a the local dnsmasq DHCP server.

SYNOPSIS

       dhcp_release <interface> <address> <MAC address> <client_id>

DESCRIPTION

       A utility which forces the DHCP server running on this machine to release a DHCP lease.

       Send a DHCPRELEASE message via the specified interface to tell the local DHCP server to delete a particular lease.

       The  interface  argument  is  the interface in which a DHCP request _would_ be received if it was coming from the client, rather than being
       faked up here.

       The address argument is a dotted-quad IP addresses and mandatory.

       The MAC address is colon separated hex, and is mandatory. It may be prefixed by an address-type byte followed by -, eg

       10-11:22:33:44:55:66

       but if the address-type byte is missing it is assumed to be 1, the type for ethernet. This encoding is the one used in dnsmasq lease files.

       The client-id is optional. If it is "*" then it treated as being missing.

NOTES

       MUST be run as root - will fail otherwise.

LIMITATIONS

       Only usable on IPv4 DHCP leases.

SEE ALSO

       dnsmasq(8)

AUTHOR

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

																   DHCP_RELEASE(1)

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