Posts Tagged ‘DHCP’

DNSMASQ is both a DNS and DHCP server that is quick and efficient to run on Linux systems and is likely already running on your Linux box. If you’re in need of a quick DHCP server to run your environment to serve multiple DHCP scopes for different subnets in your VLAN, of which we all know the best practice is subnet == VLAN == Broadcast domain, then DNSMASQ is your go to guy and I prefer it over the ISC DHCPD server. This quick tutorial will go over the basics of how to get this setup and running and assumes you’re not going to utilize the DNS service.

Create a directory for your DHCP leases file:

sudo mkdir /opt/dnsmasq

Setup dnsmasq.conf:

#
#Disable the DNS server
#
port=0
#
#Setup the server to be your authoritative DHCP server
#
dhcp-authoritative
#
#Set the DHCP server to hand addresses sequentially
#
dhcp-sequential-ip
#
#Enable more detailed logging for DHCP
#
log-dhcp
#
#Set your DHCP leases file location
#
dhcp-leasefile=/opt/dnsmasq/dnsmasq.leases
#
#Create different dhcp scopes for each of the three simulated subnets here, using tags for ID
#Format is: dhcp-range=<your_tag_here>,<start_of_scope>,<end_of_scope>,<subnet_mask>,<lease_time>
#
dhcp-range=subnet0,10.0.0.5,10.0.0.250,255.255.255.0,8h
dhcp-range=subnet1,10.0.1.5,10.0.1.250,255.255.255.0,8h
dhcp-range=subnet2,10.0.2.5,10.0.2.250,255.255.255.0,8h
#
#Setup different options for each of the unique subnets, since default gateways will be different
#The format for this is: dhcp-options=<your_tags_here>,<option>,<option_value> - 3 is router
#
dhcp-options=subnet0,3,10.0.0.1
dhcp-options=subnet1,3,10.0.1.1
dhcp-options=subnet2,3,10.0.2.1

Once this is complete, enable your DHCP service to start automatically. You should also check your systems firewall/IPTABLES service(s) to ensure you have created rules to allow UDP traffic over port 67 and port 68, or you can just flush your IPTABLES and/or disable your firewall, your choice, this isn't a security blog so I'll leave the choice to you, the person who knows their environment better.


Providing you’re either: 1. Using a hostname of the device or 2. You’re positive it will receive the same IP, if you’re using an IP address to connect to your machine using RDP that obtains its IP parameters using DHCP:

ipconfig /release && ipconfig /renew

As simple as that. In fact, you can use the same operation “&&” on a Linux box with a BASH shell using whatever interface configuration commands you’re using, if you don’t have a script which already does it for you.


We’ll just do it the “quick and dirty” way. Just start capturing all traffic on an interface. Now, in the top portion by the word “Filter:” put this syntax in udp.port == 67 or udp.port == 68

Should look like this:

wire-cap


If you have an old HP Jet Direct card (perhaps an old dot matrix printer) and you’re looking to move from static IP configuration to DHCP you’ll want to telnet into the device and change the settings that way. I am not going into detail about how to do it because the menu is very basic to navigate via the CLI. Just know that you’re better off using telnet to access the menu-driven CLI as “root” and you’ll be happy.


So, you’re wondering why and how to get an “ip-helper” address on a Comware 3com system? I wish I could say “easy enough” but I would be fibbing and giving you false expectations. I will outline what you need to do below:


dhcp enable

dhcp relay server-group 1 10.10.10.1

interface Vlan-Interface #

dhcp select relay

dhcp relay server-select 1

I am going to raise the FAIL flag on this because this is far too much work to get this working compared to other platforms that only require ONE command.


While I never recommend the use of Superscopes as they are usually relevant to a bad network design. I know that sometimes networks are inherited and not the fault of the person having to perform this action;thus, I am going to provide a lean set of steps to configure this assuming you know your way around Microsoft DHCP server and have a few requirements met: Read the rest of this entry »


Let me start by saying that Superscopes are not a standard mechanism of DHCP, just a “hack” by Microsoft to support networks that don’t understand the concept of “1 IP subnet PER vlan, not 10 IP subnets per VLAN”. The only, and I do mean ONLY, time that you use Superscopes is when you have a network design that has multiple IP subnets inside the same VLAN. Let me explain the ONLY instance where this is needed and WHY you need multiple interfaces configured for this to work… Read the rest of this entry »


The transition from Autonomous mode to Controller mode is extremely easy with the HP wireless APs. I will outline everything here Read the rest of this entry »


http://blogs.technet.com/b/teamdhcp/archive/2009/02/26/new-features-in-dhcp-for-windows-server-2008-r2-windows-7.aspx

This is supposed to “speed up” wireless client access to a network. WINDOWS DHCP FAIL! What this seems to cause is a massive headache for network and system administrators. Windows clients can forever store and cache the information from an associated SSID. Lets say a laptop hasn’t been on your network for 6 months and you just so happens you have a reservation of some sorts on the network or you changed the scope range, the wireless client will send along a DHCP proposal to get the same address it had that first time it was on there. This, as you can see, will cause headaches for you. Microsoft wants you to believe this “saves time” but in reality just how fast is the DORA process for DHCP? Typically so fast most people don’t care. Here is how you turn off Windows DHCP Network Hints:

http://blogs.technet.com/b/teamdhcp/archive/2008/12/19/how-to-configure-dhcp-network-hint.aspx