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Overview

When enabled in the SBC Edge, the DHCP client acquires the interface's IP configuration dynamically from a reachable DHCP server. Once initial configuration takes place, the DHCP client can be enabled on a per logical interface basis in the SBC. DHCP address assignment can be configured on both VLAN interfaces (VLAN 1 IP, VLAN 2 IP, etc) and port specific interfaces (i.e., Ethernet 1 IP, Ethernet 2 IP). DHCP is not supported on loopback or Admin interfaces. When enabled in the SBC, the DHCP client configures the following interface-specific attributes:

  • IP Address
  • IP Netmask
  • IP Broadcast Address

The DHCP client also dynamically configures several node-level attributes. Upon configuration of these attributes, any existing configuration is removed.

  • Default Route
  • DNS Server(s)
  • NTP Server(s)
  • Domain Name

Although enabling DHCP on multiple interfaces is supported, the recommendation is to enable only one interface with DHCP, or unexpected results may occur. If using multiple interfaces, you should assign the additional IP addresses via static configuration.

In case of IP lease renew for DHCP, or change of static IP where the new IP address is different, the existing calls will be disconnected.

Prerequisites - Setting up the DHCP client

In order to use the DHCP client on your network, the DHCP server must be on the network.

Using DHCP for System Access During Initial Configuration

When a system is in Factory Default mode, the DHCP client is enabled on Ethernet 1 and the DHCP server is enabled on Ethernet 2. This allows you to connect to the SBC without having to assign your computer a static IP.

The DHCP client acquires an IP address from DHCP server. During DHCP lease acquisition, the SBC provides the DHCP server with its hostname, which is set to the SBC node's hardware ID. If your network's DHCP and DNS servers have Dynamic DNS configured properly, the DHCP server will inform the DNS server that the SBC is reachable via its default hostname (i.e., the SBC's serial number). As a result, during initial configuration, you can access the SBC node on the network by directing your PC's browser to the node's serial number (i.e., A4025511270005.yourdocaldomain.doc). The serial number can be found on the back of the SBC unit (i.e., A4025511270005).

This default configuration is present only until initial configuration is complete. Following that, you can configure any desired DHCP functionality. The default IP addresses assigned before initial configuration are as follows:

  • SBC 2000 only:

    • Admin Port - Default address of 192.168.128.2. You can statically assign the PC an address in the 192.168.128.x subnet (i.e.,. 192.168.128.8) to connect to the SBC 2000.

  • SBC 2000 and SBC 1000:
    • Ethernet 1 – Acquires an address via a connected DHCP server.  
    • Ethernet 2 – Default address of 192.168.129.2. You can either statically assign an address to the PC in the 192.168.129.x subnet (e.g. 192.168.129.8) or the SBC 1000/2000's DHCP server will assign one (192.168.129.3).

How a DHCP Client works - Example Scenario

The DHCP client can be configured on any interface in any network layout as along as there is a DHCP server. For example, in a typical SBC 1000 branch office deployment, the SBC will have Ethernet 1 connected to the ISP WAN, and Ethernet 2 connected to the office LAN. In this scenario, the SBC's Ethernet 1 interface will acquire an IP address via DHCP from the ISP provided internet modem.

DHCP Client

 

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