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In cOS Core, any Ethernet interface or VLAN interface can act as an IPv4 DHCP client so that the IPv4 address and network for the interface can be assigned by an external DHCP server. This feature can be enabled or disabled by changing the Enable DHCP property for the interface object in the cOS Core configuration.
The default setting for different interface types are as follows:
Ethernet interfaces - The default setting for Ethernet interfaces depends on the computing platform. For Clavister products, this is specified in the relevant Getting Started Guide. For most platforms, including virtual environments, all Ethernet interfaces have the DHCP client disabled. However, in certain Clavister hardware models, a DHCP client is enabled on the interface intended for Internet connection for quick IP address configuration by an ISP's DHCP server. For the RSG-400, DHCP is disabled on all logical firewall Ethernet interfaces in the default configuration.
VLAN interfaces - DHCP is always disabled by default for VLAN interfaces.
DHCP Assignment Process Steps
As soon as DHCP is enabled on an interface and the changed cOS Core configuration is deployed, the following will occur:A DHCP lease request is issued on the DHCP enabled interface.
A listening DHCP server will issue a lease to the interface.
cOS Core will change the IPv4 address and network of the interface to become the values in the lease.
The cOS Core address book objects associated with the interface will lose their original values and take on the value 0.0.0.0 for the IPv4 address and 0.0.0.0/0 for the IPv4 network. The address book objects will not show the DHCP assigned values although these will be shown when examining the properties of the interface configuration object.
In addition to the interface address objects being assigned values, the DNS address book objects will also be assigned values if these were sent in the lease. These will allow cOS Core to look up FQDNs when required. For example, when processing certificates.
The same process of requesting a lease will also take place if cOS Core is restarted. If the DHCP is subsequently disabled on an interface, the administrator will need to manually assign the IPv4 address and network.
![[Note]](images/note.png) |
Note: Web Interface IP address icons change with DHCP |
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When IP addresses are allocated to an interface through DHCP, the address icons change in the Web Interface display so they have an asterisk in the lower left corner. |
A Renewed DHCP Lease Can Cause cOS Core Reconfiguration
If an interface in the firewall has its DHCP lease renewed, then the following should be noted:If there is no change in the values of a renewed DHCP lease then no further action is taken by cOS Core.
If any of the allocated values have changed (for example, an IP address) in a renewed DHCP lease then cOS Core will perform a reconfiguration operation, unless the next point applies.
There is one exception to the previous point. If the only change in a renewed DHCP lease is that the DNS server IP addresses are the same but the ordering is different then a reconfiguration operation in cOS Core will not occur.
This exception exists because it can sometimes be the case with an ISP that the same DNS servers are returned in a lease but in a different order. There is then no reason to perform reconfiguration and potentially disturb traffic flow through the firewall.
Example 5.1. Enabling an Ethernet Interface as a DHCP Client
This example shows how to enable the Ethernet interface If1 as a DHCP client.
Command-Line Interface
![[Important]](images/important.png)
Device:/> set Interface Ethernet If1 DHCPEnabled=YesInControl
Follow similar steps to those used for the Web Interface below.
Web Interface
