Configuring the System Mode
Topics on this page: Configuring Routable and Bridgeable Interfaces | Common Scenarios | Configuring WAN-to-WAN Bridging | 
Configuring BRAS | Configuring PPP Half Bridge Mode
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The System Mode page enables you to configure system-level operating modes that use bridging in addition or instead of routing protocols. You can also configure a feature in which the mode is selected automatically at start-up, based on the type of Internet connection detected on the LAN PC(s).

Configuring Routable and Bridgeable Interfaces

 

Making Interfaces Routable (IP-Enabled)

A routable or IP-enabled interface is simply one that has been assigned an IP address. IP-enabled interfaces are capable of forwarding IP packets. You can assign IP addresses to any LAN or WAN interface.

  • For information about assigning IP information to LAN interfaces (e.g., eth-0 and usb-0), see the help topic "Configuring the LAN and USB Interfaces."

  • For information about assigning IP information to WAN interfaces, see the help topics for PPP, EoA, and IPoA interfaces.

Making Interfaces Bridgeable (Bridge-Enabled)

When you make an interface bridgeable, you enable the software to receive Ethernet packets through that interface, for forwarding through the device’s other bridgeable interfaces. If an interface is not bridgeable, it can only forward IP packets (assuming the interface has been IP-enabled).

If you create a LAN or WAN interface, it must be IP-enabled, bridge enabled, or both. An interface that has no IP address and is not made bridgeable will not pass any data.

 

Enabling Bridging Mode

You may need to enable bridging in addition to routing if any of the following are true:

  • Your ISP may use protocols that require bridging with your LAN. The device can be configured to appear as a bridge when communicating with your ISP, while continuing to provide router functionality for your LAN.
  • Your LAN may include computers that communicate using "layer-3" protocols other than the Internet Protocol. These include IPX® and AppleTalk®. In this case, the device can be configured to act as a bridge for packets that use these protocols while continuing to serve as a router for IP data.

Follow these steps to enable bridging:

  1. Before enabling bridging, you must specify the interfaces that are capable of bridging. You specify bridgeable interfaces on the Bridging page, which displays by default when you click the Bridging tab. See Configuring Bridge Interfaces for instructions. 
  2. Redisplay the System Mode page, if necessary, by either:
    • clicking the Bridging: Enable/Disable link on the Bridge Configuration page, or
    • clicking the Home tab, and then clicking System Mode in the task bar.
  3. Click the Bridging: Enabled radio button. Do not click the other buttons (PPP Half Bridge, WAN-to-WAN bridging, BRAS) unless you want to configure these modes, which are described in the following sections. 
  4. Click Submit.

NOTE: If want your changes to be permanent, be sure to Write Settings to Flash. them.

Common Scenarios

The sections that follow describe common system configurations that use bridging, routing, or both.  

Note that you can also configure several special operating modes. These are described in Configuring Special Bridging Features.

Scenario 1: Routed Connection to ISP

In this scenario, the ISP requires customers to have a routed connection to their access server. For a routed connection, the LAN and WAN interfaces must be IP-enabled. No bridging services need to be enabled. This configuration would have these features: 

  • An Ethernet (and/or USB) interface with an IP address and network mask that identify it as being in the same subnet as your LAN PCs. Click here for instructions.
  • An IP-enabled WAN interface. The interface type can be PPP or EoA. An IPoA interface can also be used, but they are rarely used in customer settings. 
    • If an EoA interfaces is created, an IP address should be assigned to it. Or, the interface should be configured to receive an IP address through DHCP.
    • For PPP interfaces, IP information is assigned when the link is negotiated.
    • For either type of WAN interface, the Default Gateway check box is normally selected.
  • Each PC's IP properties specify the ADSL/Ethernet router's LAN interface as its gateway IP address. The PCs may also be configured to obtain IP information automatically from a DHCP server.

With this configuration, all IP packets originating from the LAN and destined for the Internet are routed to the PCs' default gateway (the LAN interface), then to the ADSL/Ethernet router's default gateway (the WAN interface), and then to the WAN interface's gateway (the ISP's access server).

In the System View page in the Home tab, the Mode field will reflect Routing. With no bridging services enabled, non-IP packets will be ignored.

Scenario 2: Bridged Connection to ISP

In this configuration, your ISP requires you to configure a bridged Internet connection. For a bridged internet connection, the WAN interface must be bridge-enabled. This configuration would have these features:

  • A bridge-enabled EoA WAN interface. Bridged IP connections must use an EoA-type WAN interface. An IP address may or may not be specified for the interface.

Note that even when the device communicates with your ISP as a bridge, its Ethernet interface must remain IP-enabled to allow you access to the  configuration program through your Web browser. The ADSL/Ethernet router can also continue to provide certain IP-based services to your LAN such as DHCP server and DNS relay. 

  • Both the LAN (eth-0 and/or usb-0) and the WAN interfaces (eoa-0) are enabled for bridging. See the help topic for the Bridge Configuration page for instructions making an interface bridgeable. 
  • The bridging service is enabled (see Enabling Bridging Mode). 
  • The ISP should provide setup instructions for the LAN PC(s), which may involve installing software (called a "PPPoE client") that  enables logging in to their servers. The PC's gateway IP address should be the IP address of the ISPs access server.

In the System View page in the Home tab, the Mode field will reflect Routing and Bridging. Although the PC uses a bridged connection to the ISP, the device recognizes at least one IP-enabled interface (eth-0), and therefore regards the device as capable of both routing and bridging.

Scenario 3: Routed and Bridged Connections to ISP

In this configuration, your LAN is like that described in Scenario 1, but also includes PCs that use a bridged Internet connection, then you should establish bridging services in addition to routing. This would also be necessary if the LAN includes PCs that use non-IP networking protocols, such has AppleTalk or IPX. This configuration would have these features:

  • An Ethernet (and/or USB) interface with an IP address and network mask that identify it as being in the same subnet as the LAN PCs. Click here for instructions.
  • An WAN interface is created for the routing path. This can be a PPP or EoA interface and must be IP-enabled, as described in Scenario 1.
  • A WAN interface for the bridging path. This must be an EoA interface. If an EoA interface was created for the routing path, the bridging path may be able to use the same interface. Check with your ISP. 
  • Bridging is enabled on the LAN interface (eth-0 and/or usb-0) and on the EoA interface to be used for the bridging path. If separate interfaces are created for the bridging and routing paths, then enable bridging only on the EoA interface to be used for bridging. See the help topic for the Bridge Configuration page for instructions making an interface bridgeable.
  • The bridging service is enabled (see Enabling Bridging Mode).
  • For the PCs that will use the routing path, the LAN interface's IP address should be specified as the IP gateway, whether assigned statically or dynamically from a DHCP server.
  • For the PCs that will use the bridging path, the ISP should provide setup instructions for the LAN PC(s), which may involve installing software (called a "PPPoE client") that  enables logging in to their servers. The PC's gateway IP address should be the IP address of the ISPs access server.

In the System View page in the Home tab, the Mode field will reflect you the Mode field will now reflect Routing and Bridging.

Configuring Special Bridging Features

The following operating mode features address special configurations. Contact your ISP for additional instructions and support information.

Configuring WAN-to-WAN Bridging

WAN-to-WAN bridging refers to the bridging of data between WAN interfaces. This can occur only when the unit is configured in bridging mode and has two or more WAN interfaces. If a packet with an unknown destination address is received from a WAN port, that packet is forwarded to all the other interfaces -- including the other bridge-enabled WAN interfaces.

This ability may not, however, be desirable for all users, due to security reasons, bandwidth constraints, etc. If this is the case, WAN-to-WAN bridging can be disabled.

Follow this procedure to enable or disable WAN-to-WAN Bridging:
  1. Before enabling bridging, you must specify the WAN interfaces that are capable of bridging. These must be EoA-type interfaces. You specify bridgeable interfaces on the Bridging page, which displays by default when you click the Bridging tab. See Enabling Bridgable Interfaces for instructions. 
  2. Redisplay the System Mode page, if necessary, by either:
    • clicking the WAN to WAN Bridging: Enable/Disable link on the Bridge Configuration page, or
    • clicking the Home tab, and then clicking System Mode in the task bar.

  3. Click the WAN-to-WAN: Enabled radio button. You do not need to enable the other bridging modes.

  4. Click Submit.

NOTE: If want your changes to be permanent, be sure to Write Settings to Flash. them.

Configuring Bridge-Router AutoSense (BRAS)

In Bridge-Router AutoSense (BRAS) mode, the device chooses at startup whether to operate in Routing and Bridging mode or Bridging-only mode, based on information it learns while communicating with the LAN PCs. This capability allows units to be delivered with one preconfiguration for both deployment types.

If BRAS is to be used, the modem must be preconfigured with both PPPoE and EoA interfaces, and bridging must be enabled (see Enabling Bridging Mode). When the modem is booted up with BRAS enabled, the mode is determined as follows:

  1. The modem comes up with both bridging and routing enabled, with its own internal PPPoE client active.
  2. If the modem subsequently detects PPPoE traffic from the LAN PC's PPPoE client (indicating a bridge deployment), then the modem automatically switches to bridging mode by stopping its own PPPoE client, causing PPPoE packets to be bridged from the LAN side.
  3. Otherwise (no PPPoE traffic is detected) the modem continues to operate as before in bridging mode (non-PPPoE traffic) as well as routing mode.

Follow these instructions to enable BRAS:

  1. Ensure that both a PPPoE and an EoA interface is established and that the EoA interface has been made bridgeable.
  2. If the System Mode page is not already displaying, click the Home tab to display the Home page, then select System Mode from the task bar.

  3. Ensure that the Bridging: Enabled radio button is selected.

  4. Click the BRAS: Enabled radio button, and then click Submit. The system  displays the following message:

System Mode Modified Successfully...

NOTE: If want your changes to be permanent, be sure to Write Settings to Flash. them.

Enabling or disabling BRAS takes effect immediately; i.e., a system reboot is not required.

 

Configuring PPP Half Bridge Mode

The ADSL/Ethernet router offers a special type of bridging mode called PPP Half Bridge mode. This mode enables the ISP to simplify the installation process for customers who will be using the device as a bridge. PPP Half Bridge mode also allows customers to use the embedded firewall features, which are normally not available on bridged connections.

Contact your ISP to determine if they offer this connection type before you configure it.

With ordinary DSL modems that use a bridged connection to the ISP, the customer must install a program on their PC called a PPP client. This program enables the customer to log in to the ISP's access server and acquire IP information that the computer needs for all subsequent Internet communication. In PPP Half Bridge mode, the ADSL/Ethernet router uses its own PPP software to communicate at startup with the ISP. The ISP assigns the IP information to the device's PPP interface, which then uses its DHCP server to pass the information on to the user's PC. Therefore, the PPP interface and the user's PC both use the same IP address.

Working with your ISP, follow this procedure to enable PPP Half Bridge mode:

  1. Ensure that your PCs are configured to accept IP information assigned by a DHCP server.
  2. Ensure that at least one PPPoE or PPPoA interface has been created on the ADSL/Ethernet router. See Configuring PPP Interfaces for instructions.

The Status field for the PPP interface must be set to Start on Data. You can modify an existing interface to set this property, if necessary.

If you have more than one computer on your LAN and your ISP provides multiple public IP addresses for those computers, you must establish a PPP interface for each public IP address.

  1. If it does not already exist, create a DHCP server pool with poolid=0. See Configuring DHCP Server for instructions.
    The pool should include at least one unique private IP address for each computer on your LAN. The gateway IP address should be set to the address of the LAN interface, which must be in the same subnet (see Configuring the LAN (Ethernet) Interface for instructions).

  2. Enable DHCP server, as described in Setting the DHCP Mode.

  3. Click the Services tab to display the NAT Configuration page. If the NAT feature is enabled, click the Disable radio button.

  4. Click the bridging tab to display the Bridging page, and then click the PPP Half Bridge: Enabled radio button. 

  5. Click the Bridging: Disabled radio button.

  6. Click Submit.

NOTE: If want your changes to be permanent, be sure to Write Settings to Flash. them.