This is known as the man-in-middle attack. If DHCP clients use the IP configuration provided by the attacker's DHCP server, the attacker can misuse their data without knowing them. The following image shows how PC2 obtains a new IP configuration from the attacker's DHCP server instead of the original DHCP server upon requesting a new IP configuration. To verify this, click a PC from the local network and change its IP configuration to Static and back to DHCP. Since the attacker's DHCP server receives the request first, it also reacts first and the client gets an IP configuration from the attacker's DHCP server. It receives DHCP requests from clients before the original DHCP server. The attacker's DHCP server is available in the local network. To force DHCP to use our pool, change the default gateway IP to the IP address of the server in the default pool.

Since DHCP clients use the 0.0.0.0 address as the source address and the default pool also uses this address as the default gateway and DNS server addresses, DHCP provides the IP configuration from the default pool instead of our pool. If multiple pools are configured, DHCP uses the source address to determine the correct pool. The following image shows how to do this.īy default, the server contains a default pool and the packet tracer does not allow us to delete it. In this pool, change the default gateway IP to the IP address that you assigned to this server. The following image shows the static IP configuration of the attacker DHCP server.Īdd a DHCP pool that replicates the DHCP pool of the original DHCP server. The following image shows our example network after adding the attacker's DHCP server. To understand how DHCP snooping protects the network from a rogue DHCP server, let's add an attacker's DHCP server to our network. The following image shows the IP configuration of the PC2 that it gets from the DHCP server. If the DHCP server is configured properly, DHCP clients get IP addresses automatically as soon as they change their IP configuration to DHCP. The following image shows this procedure. To configure PCs as DHCP clients, click the PC and click the IP configuration option from the Desktop menu item and select the DHCP option. Set the value in the DHCP Pool Options and click the Add button. The following image shows this procedure.Įnabling DHCP service and adding a DHCP poolĬlick the Services menu icon and click the DHCP Service in the left pane and select the on option in the right pane. In the IP configuration option, select the Static option and set the static configuration.

To assign a static IP address to the Server0, click Server0 and click the IP configuration option of the Desktop menu.

Router(config-if)#ip helper-address Ĭonfigure the interface to forward DHCP requests to the DHCP server.Īssigning a static IP address to the Server0

Dhcp snooping enterasys