Creating a Network Bridge in Windows XP. Why do you need a network bridge connection? A bridge between 2 Internet connections

Network Bridge simplifies the installation and configuration of small networks that use different connection types (for example, a wireless network connection and an Ethernet cable connection) by connecting different types of networks.

Network Bridge provides small businesses with additional flexibility in choosing their network type and eliminates the need to purchase additional bridges and routers.

A network bridge is used to connect LAN segments cheaply and easily. A local network segment is a part of a network medium that connects a group of computers. Most often, the network consists of several LAN segments. Before the advent of the Windows XP, Windows Server 2003, Standard Edition, and Windows Server 2003, Enterprise Edition operating systems, two methods were used to create a network containing multiple LAN segments: IP routing and bridging. IP routing requires purchasing hardware routers or setting up computers and assigning IP addresses to each computer on each network segment, as well as configuring each network segment as a separate subnet. Bridge equipment does not require such complex setup, but in this case additional bridge equipment will be required. If you use different network media types, you will need to create a separate subnet for each media type.

However, in Windows XP, Windows Server 2003, Standard Edition, and Windows Server 2003, Enterprise Edition, you have the convenient ability to connect LAN segments by selecting the Bridged Connections menu command. There is no configuration required, no need to purchase additional hardware such as bridges or routers. A network bridge automates the configuration required to route traffic between multiple network segments consisting of one or more media types.

Using a network bridge, you can connect an Ethernet network adapter, an HPNA network adapter, and a wireless adapter on PC1. Using a network bridge, you can direct traffic from one LAN segment to another and enable all computers to communicate with each other.

But what should we do if, let’s say, in such an “average network” we have a switch (three desktop computers, a couple of laptops and handhelds), but no router and access point? And I don’t really want to buy them.

That is, two different networks - a wired one, which has Internet access, and a wireless one (without it). The networks do not see each other. How to link all computers together?

We will consider the second method of connecting wired and wireless clients, using the bridge-type mechanism built into Windows XP.

To do this, we just need to insert into the computer, which is a router and has two network adapters (one facing the local network, the second to the Internet), a third network adapter, this time wireless.

It's time to activate the bridge. This mechanism will allow us to establish a "bridge" between our wired and wireless networks, so that computers from these networks can see each other.

In simple terms, a bridge is a mechanism that transparently (for working clients) connects disparate network segments. In our case, heterogeneous segments mean a wired network and a wireless network.

We configure the future computer-router. We switch local interfaces to bridge mode:
LAN - looking into a wired local network
Wireless - looking into a wireless local network

Only a bridge, by definition, operates between at least two interfaces.

Therefore, we select both local interfaces, right-click and in the menu that appears, select the “Bridge connection” item.

Windows begins the bridge creation process.

After this process is completed, another connection appears in the network connections - Network Bridge. And in the information on network adapters on which bridge mode is set, the status “Connected” appears.

The bridge is presented as a separate device; most of its parameters are the same as those of network adapters.

True, in the “properties” section there is an additional section with a list of adapters that currently belong to the bridge (there can be two or more adapters).

Actually, at this stage, all the networks that these (assigned to the bridge) adapters look at see each other directly, without routing. That is, it is as if the clients in these networks are sitting in one large homogeneous network (in other words, as if connected to one switch).

The bridge is assigned its own IP address, which is the same for all adapters assigned to the bridge connection.

Of course, there are no IP addresses in the properties of the adapters themselves. The adapter, as such, no longer exists at the logical level - there is only a bridge (with an IP address) that includes two (or more) adapters.

A network bridge manages network segments and creates one subnet for the entire network. There is no configuration required, no need to purchase additional hardware such as bridges or routers. If the IP network consists of a single subnet, IP addressing, address distribution and name resolution are greatly simplified

To connect the computers on separate LAN segments together, there are two solutions:

Create multiple network segments and connect them with routers. In this solution, each LAN segment becomes a network segment, also known as a subnet. A network segment is a portion of a network that shares the same network identifier and is bounded by routers. With multiple network segment, nodes on separate network segments send packets to a router, which forwards the packets to the destination node.

Create a single network segment using a bridge. In this solution, the separate LAN segments are bridged together to create a single network segment. With a single network segment, neighboring nodes on separate LAN segments send packets directly to each other and bridges forward the packets to the destination node on the appropriate LAN segment.

Windows XP Network Bridge

Windows XP includes the Network Bridge, a feature of the Network Connections folder that allows a computer with multiple network adapters installed to act as a bridge, connecting multiple LAN segments together to form a single network segment.

With the Network Bridge, there is no need to purchase an additional hardware-based bridge device. However, the computer running Windows XP must have network adapters installed for all the LAN segments that it is connecting together.

How to Manage Bridged Connections

To bridge LAN segments of the connections together, hold down the Ctrl key and click all the connections that correspond to all the LAN segments you want to bridge together. Then, right-click one of the selected Local Area Connection objects and click Bridge Connections

Types of Networking Connections Supported for Bridging

The Network Bridge supports all networking technologies whose device driver installed in Windows XP advertises itself as Ethernet. This includes the following types of networking technologies commonly used in home networks:
Ethernet (10 Mbps, 100 Mbps, and Gigabit Ethernet).
IEEE 802.11b wireless (also known as Wi-Fi).
Phoneline-based connections.

Additionally, the Network Bridge supports connections using IEEE 1394.

How it works

To create a single network segment from multiple LAN segments, the Windows XP Network Bridge uses the following technologies:
Layer 2 bridging.
Layer 3 bridging.

Layer 2 Bridging

Layer 2 bridging in the Network Bridge is an implementation of transparent bridging. With transparent bridging, the Network Bridge places the network adapters of the bridge in a special listening mode known as promiscuous mode. In promiscuous mode, the network adapter processes all frames received. Normally, the network adapter only processes specific frames received.

By processing all frames received on all interfaces, the Network Bridge learns which nodes are on which LAN segments by tracking the source address of received frames. The Network Bridge maintains a table of node addresses and the adapter from which the node is reachable. When a frame is received, its destination address is checked against the bridge table and if found, is forwarded without change to the LAN segment that contains the node with the destination address. If the destination address is not found, the frame is copied out all adapters except the adapter from which the frame was received, an operation known as flooding. All broadcast and multicast traffic is flooded.

The end result of the Network Bridge"s operation is that nodes on separate LAN segments can send frames directly to each other while broadcast and multicast traffic is received by every node. These are the same conditions that exist when all the nodes of the network segment are connected to the same LAN segment. Thus, the Network Bridge transparently connects multiple LAN segments and makes it logically appear as the same LAN segment.

The flooding operation of transparent bridges can cause problems when multiple bridges are configured to form a loop. One problem is a forwarding storm where a frame with an unknown destination address is forwarded endlessly between bridges. To prevent these problems, the Network Bridge implements the industry standard IEEE 802.1D Spanning Tree Algorithm (STA) to determine which network adapters on the bridges can forward frames. The result of the STA is that bridges automatically configure themselves so that you have a loop-free bridged environment at all times. There is no configuration for STA for the Network Bridge, it is enabled by default and is self-configuring.

Layer 3 Bridging

For network adapters that do not support promiscuous mode or network technologies that do not support a broadcast-based transmission method, the Network Bridge acts as a Layer 3 bridge. With Layer 3 bridging, TCP/IP hosts on different LAN segments are transparently connected by the bridge computer.

Layer 3 bridging differs from Layer 2 bridging because the frame is changed as it is forwarded by the bridge computer. Layer 3 bridging differs from routing because a Layer-3 forwarding table, not a routing table, is used for the forwarding decision.

For Layer 3 bridging, the Network Bridge also provides special handing of DHCP packets so that nodes on Layer 3-bridged LAN segments can obtain a DHCP configuration from an ICS computer.

Introduction

Network Bridge is a new feature of Windows XP that uses Layer 2 and Layer 3 bridging to transparently combine multiple LAN segments to form a single network segment. A LAN segment is collection of network nodes on the same Data Link layer link. For example, all of the computers that are connected to the same Ethernet hub comprise a LAN segment. A network segment is a collection of network nodes that share the same Network layer address. For example, a TCP/IP network segment is a subnet. All nodes on the same TCP/IP subnet share the same IP network identifier.

Layer 3 bridging

Layer 3 bridging is used if the network adapter does not support promiscuous mode. Layer 3 bridging does not require any special network adapter functionality. Layer 3 bridging only works for TCP/IP traffic. For broadcast and multicast IP traffic, a packet that is received by the Network Bridge is retransmitted out through all ports except the port on which the packet was received.

For unicast traffic, Layer 3 bridging is based on the Address Resolution Protocol (ARP). ARP is used by TCP/IP nodes to resolve the MAC address that corresponds to the next-hop address of an outbound IP packet. If the destination of the outbound IP packet is on the local subnet, the next-hop address is the destination address and ARP is used to resolve the MAC address of the destination node. If the destination of the outbound IP packet is not on the local subnet, the next-hop address is the default gateway address and ARP is used to resolve the MAC address of the default gateway (assuming that this is a typical host configuration).

A Network Bridge acts as an ARP proxy, answering ARP requests from a node on one LAN segment on behalf of a node on another segment and transferring unicast packets between nodes on different LAN segments.

The Network Bridge (Node B) connects Segments 1 and 2 and has a single IP address (IP_B). When Node A sends an IP packet to Node C, it first sends an ARP request that contains Node A"s MAC address (MAC_A), Node A"s IP address (IP_A), and Node C"s IP address (IP_C). Node B receives the broadcast ARP request and checks its Layer 3 forwarding table.

The Layer 3 forwarding table is maintained by the Network Bridge and contains entries with the following information: node IP address, node MAC address, and port (the network adapter on which the node is located). An entry for the sender of an ARP request in the Layer 3 forwarding table is created when it is received. Entries are refreshed upon each use. Unused entries are timed out after 5 minutes. In this example, the Network Bridge either creates or refreshes the following entry in the Layer 3 forwarding table: IP_A, MAC_A, Port 1.

If an entry for the target IP address of the ARP request is found in the Layer 3 forwarding table and is on a different port, the Network Bridge responds to the ARP request with an ARP reply, which contains its own MAC address for the port on which the request was received. If an entry for the target IP address of the ARP request is found in the Layer 3 forwarding table and is on the same port, the sending and destination nodes are on the same LAN segment and the ARP Request is ignored.

In this example, the Network Bridge unicasts an ARP reply to Node A with the following information: Node B"s MAC address on port 1 (MAC_B_1), Node C"s IP address (IP_C), Node A"s MAC address, and Node A's IP address (IP_A). When Node A sends packets to Node C"s IP address, they are sent to Node B"s MAC address on port 1 (MAC_B_1).

If the destination IP address of a received unicast IP packet is assigned to the Network Bridge, it is passed to IP and upper layers for processing. If the destination IP address of a received unicast IP packet is not assigned to the Network Bridge, it must determine which of the following is true:
1.The destination is a node on another LAN segment of the local subnet.

2.The destination is a node on another subnet and the packet is being forwarded to the Network Bridge because it is an IP router.

3.The destination is a node on another subnet and the packet is being forwarded to a router on another LAN segment of the local subnet.

The Network Bridge uses the following algorithm to determine which of these cases is true:
Look up the destination address in the Layer 3 forwarding table.
If an entry is found, forward the packet to the destination (Case 1 above).
If an entry is not found, use the IP routing table to determine the next-hop address for the destination address.
If a next-hop address is determined, look up the next-hop address in the Layer 3 forwarding table.
If an entry for the next-hop address is found, forward the packet to the node that corresponds to the next-hop address (Case 3 above).
If an entry for the next-hop address is not found, send the packet to IP and upper layers for processing (Case 2 above).
If a next-hop address is not determined, send the packet to IP and upper layers for processing (Case 2 above).

In this example, Node B receives the packet that is forwarded by Node A to the destination IP address (IP_C). Because the Layer 3 forwarding table contains an entry for Node C (the entry IP_C, MAC_C, Port 2), the Network Bridge forwards the packet from the MAC address MAC_B_2 (which corresponds to port 2 on the Network Bridge) to the MAC address MAC_C .

If the Network Bridge receives an ARP request and the target IP address is not found in the Layer 3 forwarding table, the Network Bridge stores the contents of the ARP request in an ARP Pending table. The Network Bridge then sends its own ARP request message out all ports except the port on which the original ARP request was received. When a unicast ARP reply to the Network Bridge"s request is received, it is matched to the entry in the ARP Pending table. The Network Bridge then sends a unicast ARP reply to the original requestor. The entry in the ARP Pending table is eventually timed out.

Windows XP Home Networking: Building Network Bridges

Network Bridge, this is a feature of the Network Connections folder that allows a computer with multiple network adapters to act as a bridge, connecting different local area network (LAN) segments. A Network Bridge is required, for example, to connect different networking technologies such as a wired Ethernet segment and a wireless 802.11b segment.

You don"t need to be connecting two networks to get value from bridging. Bridging is also useful for connecting a laptop with a built in 802.11b (wireless) card to a cabled network when you don"t have a wireless access point-add a wireless card to any other computer on your network and it can bridge the wireless onto the cabled network.

Bridging Requirements

To connect several computers, install a network card in each and run CAT5 network cabling to connect all of them to a hub (and thus each other.) The computer that will be used for bridging will need both a regular network card for the cabled connection and a wireless network card that will make the connection to the wireless access point (WAP) or gateway on the second network-in our case a Linksys WAP-11 connected to the main upstairs network. When the two networks have been bridged, the downstairs machines will be assigned IP addresses by the DHCP server and will have access to the Internet.

Differences between switches and bridges

Notes

Sources

Wikimedia Foundation. 2010.

See what a “Network bridge” is in other dictionaries:

network bridge- A device that connects two different networks that use the same addressing protocols, but may differ in higher-level protocols. Computer network topics EN network bridge… Technical Translator's Guide

Bridge, network bridge, bridge (jarg, tracing paper from English bridge) network equipment for connecting local network segments. The network bridge operates at the second level of the OSI model, providing collision domain limitation (in the case of a network Contents 1... ... Wikipedia

Bridge: Wiktionary has an entry for "bridge" A bridge is an engineering structure. Structures and mechanisms: Bridge in wooden architecture floor d... Wikipedia

Bridge is a layer 2 network device of the OSI model designed to connect segments of a computer network (or subnet) (of different topologies and architectures). The bridge, when receiving a frame from the network, checks the MAC address of the latter and if it... ... Wikipedia

This term has other meanings, see Gateway. Network gateway with built-in switch. Front view (top) and back view (bottom) Network gateway (English gateway) hardware ... Wikipedia

This article needs to be completely rewritten. There may be explanations on the talk page... Wikipedia

This article should be Wikified. Please format it according to the rules for formatting articles... Wikipedia

Bridge, network bridge, bridge (jarg, tracing paper from English bridge) network equipment for connecting local network segments. The network bridge operates at the second level of the OSI model, providing collision domain limitation (in the case of a network Contents 1... ... Wikipedia

Router used on trunk channels Router (professional jargon router, router (from the English router ... Wikipedia

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If you simply assemble a computer with two network cards and connect it to two different networks, then this computer will see all remote systems, and all members of the networks will see the router in the network environment, but nothing more. In order for computers in different segments to see each other, it is necessary to create a network bridge.
Creation of a network bridge is supported by Windows NT/2000/2003/XP
To do this, go to: “Start”>”Settings”>”Control Panel”>”Network Connections”
Select the network connections that need to be connected and right-click on them, selecting “Bridge connection” from the context menu.

A new “Network Bridge” connection will appear.

The network bridge will not work if at least one of the connections included in it has the “Automatic IP address assignment” service enabled. If possible, it is better that the IP addresses of different network segments do not overlap. There can be only one bridge, but it can include unlimited number of network interfaces . As long as the network bridge exists, changing any network parameters is impossible; if this is required for some reason, the network bridge must be deleted, corrections made, and then created again.

A network bridge is used to connect LAN segments cheaply and easily. A local network segment is a part of a network medium that connects a group of computers. Most often, the network consists of several LAN segments. Before the advent of the Windows XP, Windows Server 2003, Standard Edition, and Windows Server 2003, Enterprise Edition operating systems, two methods were used to create a network containing multiple LAN segments: IP routing and bridging. IP routing requires purchasing hardware routers or setting up computers and assigning IP addresses to each computer on each network segment, as well as configuring each network segment as a separate subnet. Bridge equipment does not require such complex setup, but in this case additional bridge equipment will be required. If you use different network media types, you will need to create a separate subnet for each media type.

Differences between switches and bridges

In general, a switch (switch) and a bridge are similar in functionality; the difference lies in the internal design: bridges process traffic using a central processor, while a switch uses a switch fabric (hardware circuitry for switching packets). Currently, bridges are practically not used (since they require a powerful processor to operate), except for situations when network segments are connected to different first-level organizations, for example, between xDSL connections, optics, Ethernet.

In the situations under consideration, the Windows XP operating system was installed on all computers.

In the first case, the cable modem was connected directly to the computer's network adapter (1). Connection to the Internet was carried out without dialing, i.e. via DHCP. I created Internet Connection Sharing for this connection. The second network device on this computer was an Edimax wireless USB adapter. Read about setting up a home wireless network in my.
When creating Internet Sharing (ICS), the second network device, in our case the wireless adapter, was automatically assigned an IP address of 192.168.0.1 with a subnet mask of 255.255.255.0. In addition, I manually assigned my ISP's DNS server addresses.
I connected the second computer (2) using a network card to the homeplug, which, in turn, connected, as expected, to the mains. I gave this computer an IP address of 192.168.0.3, a Gateway address of 192.168.0.1, and a DNS server address of 192.168.0.1

The laptop (3), I connected via an ethernet adapter to the second device with a home plug and a wireless USB adapter. Read about setting up a wireless adapter in my . Now we need to create a Network bridge for these two devices in order to combine all three computers into one network.
So, to create a network bridge you must have at least two network adapters. We go to Network Connections, select both network devices with the mouse and use the right click to call up the context menu, where we select the Network Bridge option.

We now have a third connection for which we now need to configure our network settings.

One fine day I needed to connect a virtual machine from VirtualBox to the Internet via a WiFi connection. Of course, I tried to connect using the already proven method. But no! Vig to you! Do not think that the previous method of creating a bridge for the VirtualBox virtual machine does not work, of course it does. I just didn’t immediately realize that for the created connection (bridge) you also need to enter the password to access the WiFi gateway, since the network is closed. But I guessed it after I connected using the method described below. And so let's get started! ;)

Let's start by setting up the network interface in VirtualBox. Select the installed virtual machine and on the “Details” tab, click “Network”.

As in the figure below, we go through the items marked with checkmarks. Naturally we are interested in:
1. Network Bridge
.
2. The name of the physical interface through which we connect to the network.
3. Adapter type, I usually choose PCnet-Fast III (less problems with determination, but see for yourself according to the circumstances).
4. Don't forget to check the boxes "enable network adapter" And "cable connected".

Click "OK"

Make sure that the "VirtualBox Bridged Networking Driver" component is enabled on the "Network" tab (you installed all the VirtualBox components when installing the program :))? Yes, don’t forget to check the same component for the virtual adapter!) and confidently go to the “Access” tab.

Check the box "Allow other network users to use this computer's Internet connection." Next "OK".

We receive a warning, see just above. We remember the IP indicated there (it will be needed for the control check below). And we speak boldly "Yes". By the way, I almost forgot, before this I temporarily disabled all unused network interfaces, so as not to get in the way. :)

The next step is to check the “Status” of the “VirtualBox” network connection.

See picture below.

Make sure that the IP and subnet mask are obtained correctly.

Returning to settings VirtualBox. Changing any settings in VirtualBox only possible when the virtual machine is turned off (not to be confused with the program VirtualBox :)).

On the network settings tab VirtualBox select the name of our network adapter and click “Screwdriver”.

Once again we make sure that the IP is correct and the subnet mask is obtained correctly. Well, just in case. Although we came here for the tab " DHCP server".