DHCP Server Configuration

This document details the configuration and behavior of the provided DHCP server used in the VNTD lab.

The DHCP server is hosted on the internal_server node within the Internal Services (VLAN 40) zone.

Service Activation

The service is powered by the ISC DHCP Server and runs on a dedicated internal service node. This placement ensures controlled access and avoids exposure to other zones or undesired external networks.

To make use of the service included in the server_vntd container, proceed with the following steps:

1. Topology

Set as environment variables (env) the following elements in the desired container using the server_vntd image:

DHCP_SERVER - Enable the service (any value other rather than 1 prevents the service from starting).
IFACE - Selected interface.
IP_ADDR - Address assigned to the interface.

Consideration

These values do not configure the device or the DHCP service; manual file configuration still needs to be done if the user wants to change the service configuration. Instead, they are used for the entrypoint.sh script so it waits until the interface and address are assigned to initialize the service. If the service starts before the interface or address is assigned, the service won't start.

env:
    DHCP_SERVER: 1
    IFACE: "eth1"
    IP_ADDR: "192.168.40.10"

2. Configuration Files

Bind both configuration files required for the service to work:

dhcpd.conf - Address pools and service configuration.
isc-dhcp-server - Selected interface to operate on.

binds:
    - ./config/server/dhcp/dhcpd.conf:/etc/dhcp/dhcpd.conf
    - ./config/server/dhcp/isc-dhcp-server:/etc/default/isc-dhcp-server

DHCP Software

The service is implemented using isc-dhcp-server. The server is to be explicitly bound to a single interface: eth1. This prevents the DHCP daemon from listening on unintended interfaces (even though in this scenario, all internal_server traffic is routed through the same interface).

Configuration is defined in:

/etc/default/isc-dhcp-server
/etc/dhcp/dhcpd.conf

All DHCP configuration files are stored under the project config/server/dhcp directory and mounted into the container at runtime.

Persistence

Changes made directly inside the running container are not persistent and will be lost on redeployment.

Address Definitions

The server defines dedicated pools for each user VLAN in the dhcpd.conf file:

VLAN	Subnet	IP Range	Gateway
40	192.168.40.0/24	- (Declared only)	192.168.40.1
50	192.168.50.0/24	192.168.50.10 - .254	192.168.50.1
60	192.168.60.0/24	192.168.60.10 - .254	192.168.60.1

Topology Declaration

It is necessary to declare the address of the network the DHCP device belongs to, even if it does not offer any service; otherwise, the service will not work.rt.

Clients receive as a part of their configurations the assignment of a default gateway and a DNS server address. This avoids manual client configuration and centralized configuration for ease of management.

Configuration example

    subnet 192.168.50.0 netmask 255.255.255.0 {
        range 192.168.50.10 192.168.50.254;
        option routers 192.168.50.1;
        option subnet-mask 255.255.255.0;
        option broadcast-address 192.168.50.255;
    }

Configuration example - Topology Declaration

    subnet 192.168.40.0 netmask 255.255.255.0 {
    }

The DHCP can also be configured to provide a DNS address to the clients by making use of the following:

Configuration example - Provide DNS

    option domain-name "enterprise.local";
    option domain-name-servers 192.168.10.10, 192.168.40.10;

Global Configuration

DNS settings can be applied globally, regardless of the VLAN receiving the same DNS parameters.