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linux dhcp config

 
  • Sep 16, 2019

DHCP config for testing purposes

  • platform used: 4.9.0-9-amd64 #1 SMP Debian 4.9.168-1+deb9u4 (2019-07-19) x86_64 GNU/Linux
  1. first we need to install dhcp and vlan packages copy paste the code:
sudo apt install isc-dhcp-server vlan
  1. now we need to edit two files that will allow us to use dhcp isc-dhcp-server file and dhcpd.conf file

isc-dhcp-server

isc-dhcp-server

sudo vim /etc/default/isc-dhcp-server
  • in my case I’m using enp0s31f6 interface..
# Defaults for isc-dhcp-server (sourced by /etc/init.d/isc-dhcp-server)

# Path to dhcpd's config file (default: /etc/dhcp/dhcpd.conf).
#DHCPDv4_CONF=/etc/dhcp/dhcpd.conf
#DHCPDv6_CONF=/etc/dhcp/dhcpd6.conf

# Path to dhcpd's PID file (default: /var/run/dhcpd.pid).
#DHCPDv4_PID=/var/run/dhcpd.pid
#DHCPDv6_PID=/var/run/dhcpd6.pid

 #Additional options to start dhcpd with.
# Don't use options -cf or -pf here; use DHCPD_CONF/ DHCPD_PID instead
OPTIONS=""

# On what interfaces should the DHCP server (dhcpd) serve DHCP requests?
# Separate multiple interfaces with spaces, e.g. "eth0 eth1".
INTERFACESv4="enp0s31f6"
INTERFACESv6=""

dhcp.conf

sudo vim /etc/dhcp/dhcpd.conf

  • here we need to declare all networks that we are going to use.

  • in my case I’m using 172.100.100.0/24 as my default VLAN
  • 172.100.10.0/24 as VLAN 10
  • 172.100.20.0/24 as VLAN 20
# dhcpd.conf
#
# Sample configuration file for ISC dhcpd
#

# option definitions common to all supported networks...
option domain-name "something.local";
option domain-name-servers 8.8.8.8, 8.8.4.4;

default-lease-time 600;
max-lease-time 7200;

# The ddns-updates-style parameter controls whether or not the server will
# attempt to do a DNS update when a lease is confirmed. We default to the
# behavior of the version 2 packages ('none', since DHCP v2 didn't
# have support for DDNS.)
ddns-update-style none;
deny duplicates;

subnet 172.100.100.0 netmask 255.255.255.0 {
interface enp0s31f6;

option routers 172.100.100.1;
option domain-name-servers 172.100.100.1;
option subnet-mask 255.255.255.0;
option broadcast-address 172.100.100.255;
authoritative;
pool{
        range 172.100.100.10 172.100.100.15;
}
}


#VLAN - 10

subnet 172.100.10.0 netmask 255.255.255.0 {
        option routers 172.100.10.1;
        option subnet-mask 255.255.255.0;
        option broadcast-address 172.100.10.255;
        authoritative;
        pool {
                range 172.100.10.100 172.100.10.150;
        }
}

#VLAN - 20

subnet 172.100.20.0 netmask 255.255.255.0 {
        option routers 172.100.20.1;
        option subnet-mask 255.255.255.0;
        option broadcast-address 172.100.20.255;
        authoritative;
        pool {
                range 172.100.20.100 172.100.20.150;
        }
}

# If this DHCP server is the official DHCP server for the local
# network, the authoritative directive should be uncommented.
authoritative;

# Use this to send dhcp log messages to a different log file (you also
# have to hack syslog.conf to complete the redirection).
log-facility local7;

# No service will be given on this subnet, but declaring it helps the
# DHCP server to understand the network topology.

---output omitted---

  • if you want to enable logging it is necessary to uncomment line <64>
    #log-facility local7;

  • edit the line in rsyslog.conf and create log file
    –> sudo vim /etc/rsyslog.conf - add local7.* /var/log/dhcpd.log*
    –> touch /var/log/dhcpd.log - change permissions sudo chmod 777 /var/log/dhcpd.log

  1. next step is to configure local interface to support vlan tagging
    we already installed vlan package at the beginning, so now we need to assign IP’s and VLAN’s to the interfaces:
    –> add this lines to your networks file:
iface enp0s31f6.10 inet static
    address 172.100.10.1
    netmask 255.255.255.0
    vlan-raw-device enp0s31f6

iface enp0s31f6.20 inet static
    address 172.100.20.1
    netmask 255.255.255.0
    vlan-raw-device enp0s31f6

–> or copy paste this way (edit subnets and interfaces per your requirements):

sudo ip addr add 172.100.10.1/24 dev enp0s31f6.10
sudo ip addr add 172.100.20.1/24 dev enp0s31f6.20

–> enable vlan tagging on virtual interfaces

sudo vconfig add enp0s31f6 10
sudo vconfig add enp0s31f6 20
  • I have USB and PCI network so I had to disable my USB network:
sudo ifconfig enxc8f750a56483 172.100.100.1 down

–> now bring all your interfaces up:

sudo ifconfig enp0s31f6 172.100.100.1 up
sudo ifconfig enp0s31f6.10 172.100.10.1 up
sudo ifconfig enp0s31f6.20 172.100.20.1 up
  1. now you are ready to enable isc-dhcp-server and start the service:
sudo /lib/systemd/systemd-sysv-install enable isc-dhcp-server
sudo service isc-dhcp-server start
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