Posts Tagged ‘ip helper’

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.


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.