Ethernet Bridging in computer networks.pptx

In Computer Networks, An Ethernet Bridge is a wireless device that extends a wireless network to wired devices, such as an Ethernet switch or hub, without the need for additional drivers or client software.Ethernet Bridges are wireless radios that can be used to extend a wireless network to an Ethernet switch or hub (which can be used to extend connectivity to multiple wired devices). Ethernet bridges can also be used to connect any device with an Ethernet port such as a Tivo, Xbox, or even a computer to the wireless network without having to install drivers or client software. This is a great solution for use with Mac OS and Linux computers, where drivers may be limited and more difficult to find.

Another benefit of using a wireless bridge is that since it uses wired Ethernet to deliver bandwidth to the client, you can extend the cat5 cable to its maximum segment length of 100 meters and still get connectivity. In theory, by using a Power over Ethernet (PoE) injector, you can send power over the Ethernet data cable as well and place the bridge as far away as 328 feet.Ethernet bridging essentially involves combining an ethernet interface with one or more virtual TAP interfaces and bridging them together under the umbrella of a single bridge interface. Ethernet bridges represent the software analog to a physical ethernet switch. The ethernet bridge can be thought of as a kind of software switch which can be used to connect multiple ethernet interfaces (either physical or virtual) on a single machine while sharing a single IP subnet.

By bridging a physical ethernet NIC with an OpenVPN-driven TAP interface at two separate locations, it is possible to logically merge both ethernet networks, as if they were a single ethernet subnet. When using an ethernet bridging configuration, the first step is to construct the ethernet bridge -- a kind of virtual network interface which is a container for other ethernet interfaces, either real as in physical NICs or virtual as in TAP interfaces. The ethernet bridge interface must be set up before OpenVPN is actually started. A bridge interface is a kind of virtual network interface which is formed by combining one or more ethernet interfaces, each of which may be a physical NIC or a virtual TAP interface used for VPN tunneling.
When you set up an ethernet bridge, you should manually set the IP address and subnet of the bridge interface and not use an ifconfig directive in the OpenVPN config. This is because unlike a TUN/TAP interface, OpenVPN cannot programmatically set the IP address and netmask of a bridge interface.
The OpenVPN config should specify the TAP interface component of the bridge interface in its devdirective, not the name of the bridge interface itself.
On Windows, use the dev-node directive to name the TAP-Win32 adapter which was added to the bridge (the dev-node name refers to the adapter name as shown in the Network Connections panel).
On Linux/BSD/Unix, for dev tap directive, use it explicit

1. Computer Networks ETHERNET BRIDGING Mrs. VALARMATHI K Assistant Professor Information Technology Department S.A.Engineering College

2. Bridging concept in Ethernet Introduction Bridges are datalink layer device and can connect to different networks as well as connect different networks of different types Bridges works at physical layer as well as data link layer.

3. Network Bridge A network bridge is a device that divides a network into segments . Each segment represent a separate collision domain , so the number of collision on the domain is reduced. Each collision domain has its own separate bandwidth , so a bridge also improves the network performance.

4. Types of bridges Static bridges- Mapping Table entries would be performed manually Dynamic bridge/Learning bridge/Transparent Bridge- They will automatically learn the entries and fill it. Its better than static bridges. MAC PORT A 1 B 1 C 1 D 2 E 2 F 2

5. Capabilities of Bridge Filtering Forwarding Flooding Store and forward

6. Capabilities of Bridge 1.Filtering : If any bridge finds that source MAC address and destination MAC address are on some LAN then it will not forward it and simply it will filter it.

7. Capabilities of Bridge 2 . Forwarding : If any bridge finds that source MAC address and destination MAC address are on different sides of a LAN then it will use forwarding.

8. Capabilities of Bridge 3.Flooding : if a new station added then bridge don’t know about it then flooding will be done in order to send the packet to the newly arrived station.

9. Capabilities of Bridge 4.Store and forwarding: No collision inside a bridge. Bridge will store the packet and whenever It will be convenient for bridge then it will going to forward it.

10. Spanning Tree Algorithm Step 1: Every bridge has a build in ID. The one with smallest ID will be taken as a root bridge.Eg:B1 Step 2 : Mark one port of each bridge as a root port, which is closest to root bridge. Step 3: Every LAN has choses a bridge closets to it as a designated bridge for that LAN, make that correspondent port as a designated port. Step 4: Mark the root port and Destination port as forwarding ports, block the remaining port.

11. Spanning Tree Algorithm Cycling problem of bridge is resolved by spanning tree Step 1: Root Bridge –B1

12. STEP 2: Root Port

13. STEP 3: Designated Port

14. Step 4: Mark the root port and Destination port

15. Gate Questions Q 1.Consider the diagram shown below where a number of LANs are connected by (transparent) bridges. In order to avoid packets looping through circuits in the graph, the bridges organize themselves in a spanning tree. First, the root bridge is identified as the bridge with the least serial number. Next, the root sends out (one or more) data units to enable the setting up of the spanning tree of shortest paths from the root bridge to each bridge.  Each bridge identifies a port (the root port) through which it will forward frames to the root bridge. Port conflicts are always resolved in favour of the port with the lower index value. When there is a possibility of multiple bridges forwarding to the same LAN (but not through the root port), ties are broken as follows: bridges closest to the root get preference and between such bridges, the one with the lowest serial number is preferred.

16. For the given connection of LANs by bridges, which one of the following choices represents the depth first traversal of the spanning tree of bridges? 1.A,B,,C,D 2.A,B,D,C 3.A,C,B,D 4.A,C,D,B The Answer is option (2) A,B,D,C

17. Q2. Consider the diagram shown below where a number of LANs are connected by (transparent) bridges. In order to avoid packets looping through circuits in the graph, the bridges organize themselves in a spanning tree. First, the root bridge is identified as the bridge with the least serial number. Next, the root sends out (one or more) data units to enable the setting up of the spanning tree of shortest paths from the root bridge to each bridge.  Each bridge identifies a port (the root port) through which it will forward frames to the root bridge. Port conflicts are always resolved in favour of the port with the lower index value. When there is a possibility of multiple bridges forwarding to the same LAN (but not through the root port), ties are broken as follows: bridges closest to the root get preference and between such bridges, the one with the lowest serial number is preferred.

18. For the given connection of LANs by bridges, which one of the following choices represents the depth first traversal of the spanning tree of bridges? B1, B5, B3, B4, B2 B1, B3, B5, B2, B4 B1, B5, B2, B3, B4 B1, B3, B4, B5, B2 ANSWER First select B1 as the root bridge. This selection is based on lower serial ID as given in the question. All ports of root bridge are  designated ports  and they are in  forwarding state.

19. Every non-root bridge must have a root port. All root ports are placed in  forwarding state. Root port is the port that is closest to the root bridge For example, we observe bridge B3. It has two ports leading to the root bridge. If we assume bridge-to-bridge cost as 1 unit, both these paths have the same cost. Then we will select the  lower port index  as given in the question as the root port for the bridge B3. port 3  of B3 becomes the root port.

20. Using the same logic we will find out the root ports for B5 also.

21. Coming to B4 for root port selection. We have again two different paths with the same cost. We will select  port 1  as the root port for B4  Using the same logic port 1 is selected as root port for B2 as well.

22. Designated ports The designated ports are the ports responsible for  forwarding traffic onto a network segment We have total 6 network segments or  LAN's.   Each segment will have  one  designated ports . S1 and S2 are connected to the root bridge itself via two designated ports. So no issue with segments S1 and S2 traffic .

23. Let's consider other segments. For example S3. B3,B4,B5  all can  forward  traffic to this segment S3 According to the question, we will consider only those bridges which are  nearer to the root  bridge B1. B5 and B3 are both nearer to the root bridge. Then we will break this tie by selecting the  lower bridge serial ID  i.e. B3 is selected and designated port is  port 1  of B3 for the segment 

24. Similarly, we can choose  designated ports  for S4 , S5  and s6  

25. Remaining all ports are  blocked ports.

26. This the final  spanning Tree

27. DFS traversal will give answer as  A

28. THANK YOU