Cisco 2 October 25th Define network segmentation using routers, switches and bridges Describe the basic operations of a swtich Define Ethernet switch latency Explain the difference between Layer 2 and 3.. ......... not complete list OSI Layer Application, Presentation, Session, Transport, Network (the levels the routers work on), Data Link (switches, bridges), Physical (Hub, Repeaters). Repeaters refresh the signal. Ethernet networks used ot be built using repeaters. when the performance of these ntetworks began to suffer because too many devices shared the same segment, network engineers added bridges to create multiple collision domains. As networks grew in size and complexity, the bridge evolved into the modern switch, allowing microsegmentation of the network. Today's networks are built using switches and routers, often .. routers and switching in the same function. Distance limitations Ethernet is fundamentally a shared technology where all users on a given LAN segment compete for the same available bandwidth This situation is analogous to a number of acrs all trying to access a one-lane road at the same time. Because the road has only one lane, only one ar can access it at a time. The introduction of hubs into a network resulted in more users competing for more bandwidth Bridges A bridgbe is a layer 2 device used to divide or segment a network A bridge is capable of collecting and selectively passing data frames between two network segments Bridges do this by learning the MAC address of all devices on each connected segment. Using this information, the bridge builds a briding table and forwards or blocks traffic based on that table. This results in smaller collision domains and greater network efficiency. Bridges do NOT restrict broadcast traffic. Switches Switches create a virtual circuit between two connected devices, establishing a dedicated communication path between two devices Switches on the network provide microsegmentation. This allows maximum utilization of the avaialble bandwidth. A switch is also able to facilitate multiple, simultaneous virtual circuit connections. Broadcast frames to all connected devices on the network. One broadcast frame, more collisions. Router Layer 3 device. Network layer. Used to "route" traffic betweeen two or more layer 3 networks. Routers make decisions based on groups of network addreseses, or claxssses, as opposed to individual layer 2 MAC addresses. Routers use routing tables to record the layer 3 addresses of the networks that are directly connected ot the local interfaces and network paths learned from neighboring routers. Routers are not compelled to foward broadcasts. Routers learn from their neighbors. Hello packets in EIGRPC or whatever. Factors that impact network perfromance File transfer, client/server, image processing, backup/mng, transaction processing, e-mail, desktop video Too manyt users on a 10-Mbps segment Most users accesisng one or two servers Elements of Ethernet/802.3 networks Carrier sense multiple access colision detect (CSMA/CD) Broadcast data frame delivery of Ethernet/802.3 The carrier sense multiple access/collision detect (CSMA/CD) method allows only one station to transmit at a time. Multimedia applications with higher bandwidth demand such as video and the Intern, coupled with the broadcast nature of Ethernet, can create network congestion. Normal latency is the frmames travel across trhe layers Extending the distances and increasing latency of the Ethernet/802.e LANs by using Layer 1 repeaters. Half-Duplex Originally Ethernet was ah alf-duplex technology Using half-duplex, a host could either transmit or receive at one time, but not both If the network is already in use, the transmission is delayed When a collision occurs, the host that the first detects the collision will send out a jam signal to the other hosts. Upon receiving the jam signal, each host will stop sending data, then wait for a random period of time berfore attempting to retransmit. The back-off algoirhtm generates this random delay. As mnore hosts are added to the network, and begin transmitting, collisions are more likely to occur. More hosts? More colliiosn -- obvious Duplex Transmissions Simplex Transmission: One way and only one way only. One way street. Half-duplex Full duplex Network congestion Today's networks are expericing an increase in the transmission of many forms of media: Large graphics,m images, video, applicatuonsn Latency or delay is thetime a frame or a packet takes to travel from the source station to the final destination It is important to quanitfy the total latencty of the path between the source and the destination ofr LANs and WANs. Latency has at least three sources: First, there is the time it takes the source NIC to place voltage pul;eses on the wire and the time it takes the receiving NIC to interpret these pulses. This is sometimes called NIC delay. Second, there is the actual propogation delay as the signal takes time to trravel along the cable. Third, latency is added according to which network devces whetehr theyt are layer 1, 2, or 3, are added to the path between the two communicating computers. Ethernet 10 BASE-T transmission time Transmission time equals the number of bits being sent times the time for a given technology. Another way to think about transmission time is the The benefits of using repeaters The distance that a LAN cna conver is limited due to attenuation not finished Full-duplex transmitting Full duplex ethernet allows the tranismsion of a packet and the reception of a different packet at the same time To transmit and receive at once, a dedicated siwtch port is required for each node. The full-duplex eEthernet switch takes advantage of the two pairs of wires in the cable by creating a direct connection between the transmit and blah blah blah not complete LAN segmentation For example, a bridge, a lan switch, and a router. There are Collision Domain 1, Collision Domain 2, and Collision Domain 3. What are collision domains? What is lan segmentation? hOw do you create more collision domains? Is creating more collision domains good? Yes. Bridge creates collision domains. The lan switch gives more bandwidth at each port, is kind of the same. Sending and receiving ethernet frames on a bus When an Ethernet frame ise sent out on the bus all devices on the bus receive it. What do they do with it? Preamble, Destination Address, Source Address, Type, Date, Pad, CRC Each NIC card compares its own MAC address with the Destination MAC address If it matches, it copines in the rest of the farame. If it does not match, it ignores the rest of the frame. ... So what happens when multiple computers tranmist at the same time? Collision occurs Access Methods Non-Deterministic: Contention methods. Only one signal can be on the network at any one time. CSMA/CD (Carirer Sense Multiple Access with Collision Detection) Listense to the networks' shared edia to see if any other users on "on the line" by trying to sense a netural electrical signal or carrier. If no transmission is sensed, then the multiple access allows anyone onto the media without any furhter permission required. If tow PCS detect a netural signal, balh blah blah not complete What does a hub do when it receives information? How does a hub deal with frames? What later is the hub on? A hub is nothing more than a multiport repeater. Switch versus Hub ... Hub is a repeater, layer 1 device. Traffic forwarded out all portst. Incomming traffic is onoy one port. That's not good. You only want to send it to the person who wants, it really. The hub will flood it out all ports except for the incomming port. Hub is a layer 1 device A hub does NOT ,look at layer 2 addresses, so it is fast in transmitting data. Disadvantage iwth hubs: A hub or series of hubs is a single collision domain. A lot of time is spent because of this. A collision will occur if any two or more deivdcesc transmit at the same time within the collision domain. More on this later. If you add 10 computers to a hub, there would constantly be ccollision, pretty much. A switch, on the other hand, traffic is only forwared out of the destination port. Switches are also known as learning bridges or learning switches. A switch has a source address table in cache (RAM ) where it stores source MAC address after it learns about them. A switch receives an ethernet frame it searches the source address table for the destination MAC address. If it finds a match, it filters the frame by only sending it out that port. If there is not a match it floods it out all ports. it is kind of like a routing table, essentially. When there is only one device on a swtich port, the collision domain is only between the PC ... balh Transparent Bridging Transparent bridging normal swtiching process is defined in IEEE 802.1d describe the five bridging process. Receive packet, learn source address or refresh aging timer, Is the destination a broadcast, multicast or unknown unicast? Are the source and destination on the same interface? Forward and unicoast to correct port. What is the difference between unicast, multicast, and broadcast? Broadcast v. Multicast --> Broadcast is to everybody, multicast is to a selected group.