Network Bridge

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Network Bridge

Network Bridge makes it inexpensive and easy to connect LAN segments. A LAN segment is a section of network media that connects computers. Frequently, a network has more than one LAN segment. Prior to Windows XP; Windows Server 2003, Standard Edition; and Windows Server 2003, Enterprise Edition, if you wanted to have a network with more than one LAN segment, then you had two options: IP routing and hardware bridging. IP routing required you to buy hardware routers or configure computers to act like routers, configure IP addressing for each computer on each network segment, and configure each network segment as a separate subnet. Hardware bridging did not require difficult configurations, but it did require you to purchase hardware bridges. Additionally, if you were using different types of network media, you needed to create a separate subnet for each type of media.

In contrast, the Network Bridge feature that is available with Windows XP; Windows Server 2003, Standard Edition; and Windows Server 2003, Enterprise Edition allows you to connect LAN segments simply by clicking the Bridge Connections menu command. No configuration is required, and you do not need to purchase additional hardware, such as routers or bridges. Network Bridge automates the configuration that is required to route traffic between multi-segment networks that consist of a single type of media or mixed media.

Network Bridge example

Suppose you have a small office network with four computers (PC1, PC2, PC3, and PC4) and one Ethernet hub. The four computers are running Windows XP; Windows Server 2003, Standard Edition; or Windows Server 2003, Enterprise Edition and have the following hardware installed:

• PC1 has an adapter connecting it to the Internet, an Ethernet network adapter, an HPNA network adapter, and a wireless adapter.

• PC2 has an Ethernet network adapter.

• PC3 has an HPNA network adapter.

• PC4 has a wireless network adapter.

The Ethernet adapters on PC1 and PC2 are connected to a common Ethernet hub to form the first LAN segment. PC1 is connected to PC3 with the HPNA adapter to form a second LAN segment, and PC1 is connected to PC4 with the wireless adapter to form a third LAN segment.

You can use Network Bridge to connect the Ethernet network adapter, the HPNA network adapter, and the wireless network adapter on PC1. Network Bridge can forward traffic from one LAN segment to another and enable all of your computers to communicate with each other.

Without Network Bridge (or additional routing configurations or bridging hardware), only PC1 can communicate with each of the other computers because PC1 is the only computer that has connections to all three LAN segments. Because PC2, PC3, and PC4 use different types of network media, they are on different LAN segments, and they are unable to communicate with any computer other than PC1 (without Network Bridge or additional routing configurations or bridging hardware).

Network Bridge considerations

Only one bridge can exist on a computer, but it can be used to bridge as many different network connections as the computer can physically accommodate. For information about creating Network Bridge, see Set up Network Bridge.

In order to include the ICS private connection as part of a Network Bridge, you must temporarily disable ICS. Be careful not to include the ICS public connection as part of a Network Bridge. To do so creates an unprotected link between your network and the Internet, leaving your network vulnerable to intrusions, and prevents you from enabling ICF or ICS. For more information about using ICS, see Connecting to the Internet in a home or small office network.

Only Ethernet, IEEE-1394 adapters, or Ethernet-compatible adapters, such as wireless and Home Phoneline Network adapters, can be a part of Network Bridge. Network Bridge with a wireless or IEEE-1394 connection supports traffic using Internet Protocol version 4 (IPv4) only.

Spanning tree algorithm

Network Bridge uses the IEEE spanning tree algorithm (STA) to establish a loop-free forwarding topology. When there are multiple paths in a bridged network, loops can form, and the simple forwarding rules of a bridge can cause forwarding storms--a condition in which the same frame is relayed endlessly from one network segment, across the bridge, to another segment. STA provides an automated mechanism to selectively disable bridge forwarding on individual ports as is necessary, in order to ensure that the network topology is loop-free. There is no configuration needed to configure Network Bridge for STA.

Note

• Internet Connection Sharing and Network Bridge are not included in Windows Server 2003, Web Edition; Windows Server 2003, Datacenter Edition; and the Itanium-based versions of the original release of the Windows Server 2003 operating systems.