Network Bridges and Routers

1. Network Bridges and Routers Brandon York

2. What exactly is a Bridge in Networking? _____________________________________ A Bridge is a device that filters data traffic at a network boundary. Bridges reduce the amount of traffic on a LAN by dividing it into two segments. It connects on the data-link layer, (layer 2) of the OSI model. In the picture to the right, the data is coming from the database server. The bridge filters the data, sending the data to the correct locations.

3. How does a bridge work?___________________________ Bridges are similar to repeaters and network hubs, devices that connect at the physical layer, however, with bridging, traffic from one network is managed rather than simply rebroadcast to adjacent network segments. Bridges tend to be more complex than hubs or repeaters. Bridges can analyze incoming data packets to determine if the bridge is able to send the given packet to another segment of the network

4. Bridges Continued___________________________ Since bridging takes place at the data-link layer of the OSI model, a bridge processes the information from each frame of data it receives. In an Ethernet frame, this provides the MAC address of the frame's source and destination. Bridges use two methods to resolve the network segment that a MAC address belongs to.

5. The Data-Link Layer The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.

6. The Data-Link Layer!

7. Transparent Bridging This method uses a forwarding database to send frames across network segments. The forwarding database is initially empty and entries in the database are built as the bridge receives frames. If an address entry is not found in the forwarding database, the frame is rebroadcast to all ports of the bridge, forwarding the frame to all segments except the source address. By means of these broadcast frames, the destination network will respond and a route will be created. Along with recording the network segment to which a particular frame is to be sent, bridges may also record a bandwidth metric to avoid looping when multiple paths are available. Devices that have this transparent bridging functionality are also known as adaptive bridges. They are primarily found in Ethernet networks.

8. Source Route Bridging Source route bridging is used primarily on token ring networks.The spanning tree protocol is not used, the operation of the network bridges is simpler, and much of the bridging functions are performed by the end systems, particularly the sources. A field in the token ring header, the routing information field (RIF), is used to support source-route bridging. Upon sending a packet, a host attaches a RIF to the packet indicating the series of bridges and network segments to be used for delivering the packet to its destination. The bridges merely follow the list given in the RIF - if a given bridge is next in the list, it forwards the packet, otherwise it ignores it. Loops are avoided by requiring each bridge to ignore packets which already contain its bridge number in the RIF field.

10. Bridge History Bridges were one of the first network devices. Early bridges were more intelligent than network repeaters and faster than routers. Although bridges are rarely used in modern-day networks, it is important to understand their function as many modern-day network devices are based on the principles first pioneered by the network bridge. Bridges became popular in the late 1980s and reached the peak of their popularity in the late 1990s. Since that time, bridges have been losing ground due to the invention of the network switch.

11. Network Bridge Manufacturers Just to name a few… Pulsar Linksys Cisco

12. Price.. 9$ to 17,000$

13. Yes… 17,000 dollars. 9 dollars

14. What is a Router? Its an electronic device used to connect two or more computers or other electronic devices to each other, and usually to the Internet, by wire or radio signals. This allows several computers to communicate with each other and to the Internet at the same time. More technically, a router is a networking device whose software and hardware are usually assigned to the tasks of routing and forwarding information. Routers operate on 3rd layer of the OSI model. The network layer.

15. Router Table What is it?: Its an electronic file, database type object that is stored in a router or a networked computer. The routing table stores the routes to particular network destinations. This information contains the topology of the network immediately around it. The construction of routing tables is the primary goal of routing protocols and static routes. Routing tables are generally not used directly for packet forwarding in modern router architectures; instead, they are used to generate the information for a smaller forwarding table which contains only the routes which are chosen by the routing algorithm as preferred routes for packet forwarding, often in a compressed or pre-compiled format that is optimized for hardware storage and lookup.

16. The Two Planes of Routing • Control plane: in which the router learns the outgoing interface that is most appropriate for forwarding specific packets to specific destinations. • Forwarding plane: which is responsible for the actual process of sending a packet received on a logical interface to an outbound logical interface.

17. Types of Routers • Edge Router: Placed at the edge of an ISP network, it speaks external BGP (eBGP) to a BGP speaker in another provider or large enterprise Autonomous System(AS) . • Subscriber Edge Router: Located at the edge of the subscriber's network, it speaks eBGP to its provider's AS(s). It belongs to an end user (enterprise) organization.

18. Types Cont. • Inter-provider Border Router: Interconnecting ISPs, this is a BGP speaking router that maintains BGP sessions with other BGP speaking routers in other providers' ASes • Core router: A router that resides within the middle or backbone of the LAN network rather than at its periphery

19. Types cont… • Access routers: are located at customer sites such as branch offices that do not need hierarchical routing of their own. Typically, they are optimized for low cost.

20. History of Routers • The idea for a router (although they were called "gateways" at the time) initially came about through an international group of computer networking researchers called the International Network Working Group (INWG). Set up in 1972 as an informal group to consider the technical issues involved in connecting different networks.

21. History Cont. • The idea was explored in more detail, with the intention to produce a real prototype system, as part of two contemporaneous programs. One was the initial DARPA-initiated program, which created the TCP/IP architecture of today.

22. History Cont… … … … … … … • The first true IP router was developed by Virginia Strazisar at BBN, as part of that DARPA-initiated effort, during 1975-1976. By the end of 1976, three PDP-11-based routers were in service in the experimental prototype Internet. The first multiprotocol routers were independently created by staff researchers at MIT and Stanford in 1981. Virtually all networking now uses IP at the network layer, multiprotocol routers are largely obsolete, although they were important in the early stages of the growth of computer networking.

23. Router Manufacturers D-Link, NetGear, Linksys, TrendNet, Belkin, Cisco, Buffalo, SMC, USRobotics, TP-Link, Asus, 3Com, Syswan, Zonet, Edimax, HP, Hawking, and Encore.

24. Sources