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Bridging/Switching               CMC Limited
Objectives  •   Understand purpose of using bridges and switches.  •   Explain functions of switch at layer 2.  •   Unders...
Bridges Bridges are data communication devices that operate principally at Layer 2 of the OSI reference model. Bridges are...
Bridges contd..When a frame comes into a bridge interface, the bridgeexamines the layer-2 destination address of the frame...
Bridges contd..In order to make better use of the network and reduce thenumber of collisions, we may use network bridge. T...
Bridges contd..A bridge will always forward all frames with “unknown”destination MAC addresses to all connected interfaces...
Bridges contd..Types of Bridges Bridges can be grouped into categories based on various product characteristics. Using one...
Types of Bridges contd..     CMC Limited
Bridges contd..Bridge Forwarding and Filtering Filtering is the ability of a bridge to determine whether a frame should be...
SwitchesSwitching technology has emerged as the evolutionary heirto bridging-based internetworking solutions.Superior thro...
Switches contd..CMC Limited
Bridging vs. Switching •   Bridges are software based, while switches are     hardware based because they use ASIC (Applic...
Switch Functions at Layer 2 There are three distinct functions of layer 2 switching.      •   Address learning      •   Fo...
Switch Functions at Layer 2 Contd..Address Learning If a device answers and sends a frame back, then the switch will take ...
Address Learning Contd..Node 2 Sends a Frame to Node 1:                       Internal Digital Bus      NODE 1            ...
Switch Functions at Layer 2 Contd..Forward/Filter Decision When a frame arrives at the switch, the first step is to check ...
Switch Functions at Layer 2 Contd..Loop Avoidance If multiple connections between switches are created for redundancy purp...
Loop Avoidance contd..Things will work fine until a broadcast come along andcauses a lot of trouble.  Server              ...
Switch TypesSwitches are fast, therefore have low latency. This latencydoes vary and depends on what type of switching mod...
Switch Types Contd..Cut-through In this mode the switch reads the frame until it learns the destination MAC address of the...
Switch Types Contd..Fragment Free The Fragment free switching method is mainly used to check for frames which have been su...
Switch Types Contd..Different Switching Modes within a Frame.                                                             ...
Configure a Switch The Catalyst 1900 switch can now use a command line interface (CLI) to configure the Cisco Internetwork...
Configure a Switch Contd..Switch StartupYou have to check the following before you power on theswitch for the first time: ...
Switch Startup contd..1 user(s) now active on Management Console.User Interface Menu[M] Menus[K] Command Line[I] IP Config...
Configure a Switch Contd..Setting PasswordThe first thing that you should configure on a switch is thepasswords. You don’t...
Setting Password contd..To enter the user-mode password, use level 1. To enter theenable-mode password, use level 15. Alwa...
Setting Password contd..You can use the command show running-config to see thecurrent configuration on the switch.#sh runB...
Configure a Switch Contd..Setting HostnameIt is helpful to set a hostname on a switch so that you canidentify the switch w...
Configure a Switch Contd..Setting IP Information You do not have to set any IP configuration on the switch to make it work...
Setting IP Information contd..To set the IP configuration on a 1900 switch, use the ipaddress command. The default gateway...
Configure a Switch contd..Verify IP Connectivity It is important to test the switch IP configuration. You can use the Ping...
Configure a Switch contd..Verify IP Connectivity It is important to test the switch IP configuration. You can use the Ping...
Configure a Switch contd..Port Duplex By using duplex command in the interface configuration you can set the duplex on the...
Configure a Switch contd..LAN Switch Type You can change LAN switch type with the switching-mode command from global confi...
Spanning Tree Protocol (STP)Spanning Tree allows you to implement redundancy in aswitched or bridged network without needi...
Spanning Tree Protocol (STP) contd..Root Bridge Selection At the boot-up all of the bridges think of themselves as the Roo...
Spanning Tree Protocol (STP) contd..Spanning Tree Port States Each port on a bridge or switch using Spanning-Tree Protocol...
Virtual LAN (VLAN) VLAN is a networking technology that allows networks to be segmented logically without having to be phy...
Switches – the Core of VLANs Switches are one of the core components of VLAN communications.  Switches provide the intelli...
VLAN Memberships VLANs are usually created by an administrator, who then assigns switch ports to each VLAN. Such a VLAN is...
Configure VLANs on a SwitchYou can create up to 64 VLANs on a 1900 switch. Aseparate spanning-tree instance can be configu...
Configure VLANs on a Switch contd..VLAN BenefitThere are several benefits to using VLANs. To summarize,VLAN architecture b...
Configure VLANs on a Switch contd..VLAN LimitationThere are a few limitations to using VLANs, some of themare as follows  ...
VLAN Trunk Protocol (VTP)The goal of VLAN Trunk Protocol (VTP) is to manage allconfigured VLANs across a switched internet...
VLAN Trunk Protocol (VTP) contd..VTP ModeVTP-capable devices can be configured to operate in thefollowing three modes:  • ...
Configuring Trunk Ports The 1900 switch only runs the Dynamic Inter-Switch Link (DISL) encapsulation method. To configure ...
Configuring Trunk Ports contd..Verifying Trunk LinksTo verify your trunk ports, use the show trunk command.If you have mor...
VTP Configuration on Catalyst Switches To configure VTP, first configure the domain name you want to use. Once you configu...
VTP Configuration on Catalyst Switches contd..Configuring the Domain When you create the VTP domain, you have the option t...
VTP Configuration on Catalyst Switches contd..VTP Pruning If you turn VTP pruning on in a VTP server, you turn it on for t...
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Chapter4

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  1. 1. Bridging/Switching CMC Limited
  2. 2. Objectives • Understand purpose of using bridges and switches. • Explain functions of switch at layer 2. • Understand different switching mode. • Understand how to configure a switch. • Understand Spanning Tree Protocol. • Explain Virtual LAN. • Understand VLAN Trunk Protocol. CMC Limited
  3. 3. Bridges Bridges are data communication devices that operate principally at Layer 2 of the OSI reference model. Bridges are full-fledged packet switches that forward and filter frames using the LAN destination addresses. A bridge connects two segments of the same network. There are several functions provided by bridges: traffic isolation, frame forwarding and filtering. CMC Limited
  4. 4. Bridges contd..When a frame comes into a bridge interface, the bridgeexamines the layer-2 destination address of the frame andattempts to forward the frame on the interface that leads tothe destination. CMC Limited
  5. 5. Bridges contd..In order to make better use of the network and reduce thenumber of collisions, we may use network bridge. Thepurpose of the bridge was to segment the network in anumber of smaller collision domains. The job of a bridge wassimply to help ensure that the “scope” of collisions wasmade smaller. MAC Interface Address Computer 1 A Computer 2 A Computer 3 B Computer 4 B Computer 5 C Computer 6 C CMC Limited
  6. 6. Bridges contd..A bridge will always forward all frames with “unknown”destination MAC addresses to all connected interfaces,besides the one the transmission originated on.One limitation of a bridge is that they typically support nomore than 16 interfaces. CMC Limited
  7. 7. Bridges contd..Types of Bridges Bridges can be grouped into categories based on various product characteristics. Using one popular classification scheme, bridges are either local or remote. Local bridges provide a direct connection between multiple LAN segments in the same area. Remote bridges connect multiple LAN segments in different areas, usually over telecommunications lines. CMC Limited
  8. 8. Types of Bridges contd.. CMC Limited
  9. 9. Bridges contd..Bridge Forwarding and Filtering Filtering is the ability of a bridge to determine whether a frame should be forwarded to some interface or should just be dropped. Forwarding is the ability to determine the interfaces to which a frame should be directed. Bridge filtering and forwarding are done with a bridge table. A nodes entry in the bridge table contains: • LAN address of the node • bridge interface that leads toward the node • time at which the entry for the node was placed into the table CMC Limited
  10. 10. SwitchesSwitching technology has emerged as the evolutionary heirto bridging-based internetworking solutions.Superior throughput performance, higher port density,lower per-port cost and greater flexibility have contributedto the emergence of switches as replacement technologyfor bridges.When you think of a switch, simply consider it to be a fasterbridge with more ports. CMC Limited
  11. 11. Switches contd..CMC Limited
  12. 12. Bridging vs. Switching • Bridges are software based, while switches are hardware based because they use ASIC (Application- Specific Integrated Circuit) chips to help make filtering decisions. • Switches have a higher number of ports than most bridges. • Bridges can only have one spanning-tree instance per bridge, while switches can have many. • Both bridges and switches forward layer-2 broadcasts. • Both bridges and switches make forwarding decisions based on layer-2 addresses. CMC Limited
  13. 13. Switch Functions at Layer 2 There are three distinct functions of layer 2 switching. • Address learning • Forward/filter decisions • Loop avoidance CMC Limited
  14. 14. Switch Functions at Layer 2 Contd..Address Learning If a device answers and sends a frame back, then the switch will take the source address from that frame and place the MAC address in the database, associating this address with the interface that received the frame. Node 1 Transmits Data to Node 2 for First Time. Internal Digital Bus NODE 1 (Transmitting) NODE 4 NODE 2 NODE 5 (Receiving) NODE 3 NODE 6 CMC Limited
  15. 15. Address Learning Contd..Node 2 Sends a Frame to Node 1: Internal Digital Bus NODE 1 NODE 4 (Receiving) NODE 2 NODE 5 (Transmitting) NODE 3 NODE 6 Frame Path after MAC/Port is known: Internal Digital Bus NODE 1 (Transmitting) NODE 4 NODE 2 NODE 5 (Receiving) NODE 3 NODE 6 CMC Limited
  16. 16. Switch Functions at Layer 2 Contd..Forward/Filter Decision When a frame arrives at the switch, the first step is to check the destination hardware address, which is compared to the forward/filter MAC database. If a device answers to the broadcast, then the MAC address of that device is added to the MAC database of the switch. CMC Limited
  17. 17. Switch Functions at Layer 2 Contd..Loop Avoidance If multiple connections between switches are created for redundancy purpose, network loops can occur. Server Port 1 Port 1 Switch A Switch B Port 2 Port 2 Two switches which have been placed in the network to provide redundancy in case one fails. CMC Limited
  18. 18. Loop Avoidance contd..Things will work fine until a broadcast come along andcauses a lot of trouble. Server First Round Second Round Port 1 Third Round Port 1 Switch A Switch B Port 2 Port 2 First Round CMC Limited
  19. 19. Switch TypesSwitches are fast, therefore have low latency. This latencydoes vary and depends on what type of switching mode theswitch is operating at.There are three switching modes: • Cut-through • Fragment Free • Store-and-forward CMC Limited
  20. 20. Switch Types Contd..Cut-through In this mode the switch reads the frame until it learns the destination MAC address of the frame it’s receiving. This method has the following features: • Lowest latency • Lowest error checking • Highest frame forwarding speed CMC Limited
  21. 21. Switch Types Contd..Fragment Free The Fragment free switching method is mainly used to check for frames which have been subject to a collision. The frame’s first 64 bytes are only checked before forwarding the frame out of the designated port.Store-and-forward In this mode, when the switch receives a frame from one of it’s ports, it will store it in memory, check it for errors and corruption, and if it passes the test, it will forward the frame out of the designated port, otherwise, if it discovers that the frame has errors or is corrupt, it will discard it. CMC Limited
  22. 22. Switch Types Contd..Different Switching Modes within a Frame. Up to 15006 bytes 1 byte 6 bytes 6 bytes 2 bytes bytes 4 bytes Start of Frame Frame Destination Source CheckPreamble Delimiter Hardware Hardware Length DATA Sequence (SFD) Address Address (FCS) Cut-through: No error checking Fragment Free: Checks for collisions Store-and-forward: All errors filtered; has highest latency CMC Limited
  23. 23. Configure a Switch The Catalyst 1900 switch can now use a command line interface (CLI) to configure the Cisco Internetworking Operating System (IOS) on the switch. Before the CLI was available, the 1900 switch could only be configured through a menu system. There are two types of operating systems that run on Cisco switches: • IOS-based: In this system, you can configure the switch from a CLI. • Set-based: This system uses older CLI configuration commands (you can use the set command to configure the switch). CMC Limited
  24. 24. Configure a Switch Contd..Switch StartupYou have to check the following before you power on theswitch for the first time: • You have plugged in all the network cables securely. • You have connected a terminal to the console port. • You have configured your terminal software correctly.When the 1900 switch is first powered on, it runs through apower-on self-test (POST). After the POST runs and youhave a console cable connected to the switch, the menushown next appears. CMC Limited
  25. 25. Switch Startup contd..1 user(s) now active on Management Console.User Interface Menu[M] Menus[K] Command Line[I] IP ConfigurationEnter Selection: KCLI session with the switch is open.To end the CLI session, enter [Exit].>By pressing K, you can use the command-line interface,and when you press M, you will be allowed to configure theswitch through a menu system. Pressing I allows you toconfigure the IP configuration of the switch. CMC Limited
  26. 26. Configure a Switch Contd..Setting PasswordThe first thing that you should configure on a switch is thepasswords. You don’t want unauthorized users connectingto the switch.The following output is an example of how to set both theuser-mode and enable-mode passwords on the 1900switch.(config)#enable password level 1 rahul(config)#enable password level 15 rahull(config)#exit#exit CMC Limited
  27. 27. Setting Password contd..To enter the user-mode password, use level 1. To enter theenable-mode password, use level 15. Always rememberthe password must be at least four characters, but notlonger than eight characters.Enable Secret PasswordThe enable secret password is a more secure passwordand supercedes the enable password if set. If you have anenable secret set, you don’t even need to bother setting theenable-mode password.(config)#enable secret rahul2 CMC Limited
  28. 28. Setting Password contd..You can use the command show running-config to see thecurrent configuration on the switch.#sh runBuilding configuration...Current configuration:enable secret 5 $1$FMFQ$wFVYVLYn2aXscfB3J95.w.enable password level 1 “RAHUL”enable password level 15 “RAHUL1” CMC Limited
  29. 29. Configure a Switch Contd..Setting HostnameIt is helpful to set a hostname on a switch so that you canidentify the switch when connecting to it.You can use the hostname command to set the hostnamein the 1900 switch.>enEnter password: ******#config tEnter configuration commands, one per line.End with CNTL/l(config)#hostname Rahul1900ENRahul1900EN(config)# CMC Limited
  30. 30. Configure a Switch Contd..Setting IP Information You do not have to set any IP configuration on the switch to make it work. You can manage the switch via Telnet or other management software, or if you wanted to configure the switch with different VLANs and other network functions. By using the command show ip (or sh ip), you can see the default IP configuration of the switch. CMC Limited
  31. 31. Setting IP Information contd..To set the IP configuration on a 1900 switch, use the ipaddress command. The default gateway should also be setusing the ip default-gateway command.Rahul1900EN#config tEnter configuration commands, one per line.End with CNTL/ZRahul1900EN(config)#ip address 172.16.10.16255.255.255.0Rahul1900EN(config)#ip default-gateway172.16.10.1Rahul1900EN(config)# CMC Limited
  32. 32. Configure a Switch contd..Verify IP Connectivity It is important to test the switch IP configuration. You can use the Ping program, and you can telnet into the 1900 switch.Rahul1900EN#ping 172.16.10.10Sending 5, 100-byte ICMP Echos to 172.16.10.10, time out is 2 seconds:! ! ! ! !Success rate is 100 percent (5/5), round-tripmin/avg/max 0/2/10/ ms CMC Limited
  33. 33. Configure a Switch contd..Verify IP Connectivity It is important to test the switch IP configuration. You can use the Ping program, and you can telnet into the 1900 switch.Configure Switch Interfaces It is important to understand how to access switch ports. The 1900 switch uses the type slot/port command.Interface Descriptions You can administratively set a name for each interface on the 1900 switch. You cannot use spaces with the description command, but you can use underscores if you need to. CMC Limited
  34. 34. Configure a Switch contd..Port Duplex By using duplex command in the interface configuration you can set the duplex on the 1900 switch.Erasing Switch Configuration The switch configuration is stored in NVRAM. You cannot view the startup-config, or contents of NVRAM. You can only view the running-config. CMC Limited
  35. 35. Configure a Switch contd..LAN Switch Type You can change LAN switch type with the switching-mode command from global configuration mode.MAC Address Table The switches use MAC (hardware) addresses burned into a host’s network interface card (NIC) to make forwarding decisions. CMC Limited
  36. 36. Spanning Tree Protocol (STP)Spanning Tree allows you to implement redundancy in aswitched or bridged network without needing to worry aboutthe broadcast storm.Operation of the Spanning Tree ProtocolThe job of STP is to find all links in the network and shutdown any redundant once, thereby preventing networkloops from occurring. CMC Limited
  37. 37. Spanning Tree Protocol (STP) contd..Root Bridge Selection At the boot-up all of the bridges think of themselves as the Root Bridge.Election of Designated Ports The bridge containing the designated port for a given segment is referred to as the designated bridge for that segment. CMC Limited
  38. 38. Spanning Tree Protocol (STP) contd..Spanning Tree Port States Each port on a bridge or switch using Spanning-Tree Protocol exists in one of the following five states: • Blocking • Listening • Learning • Forwarding • DisabledConvergence Convergence occurs when bridges and switches have transitioned to either the forwarding or blocking modes. CMC Limited
  39. 39. Virtual LAN (VLAN) VLAN is a networking technology that allows networks to be segmented logically without having to be physically rewired.Extending VLANs Between Switches In order to extend VLANs across different switches, a trunk link must interconnect the switches. A trunk link is implemented between fast switch ports on two different switches using a crossover cable. CMC Limited
  40. 40. Switches – the Core of VLANs Switches are one of the core components of VLAN communications. Switches provide the intelligence to group users, ports, or logical addresses into common communities of interest. LAN switches offer significant increases in performance and dedicated bandwidth across the network, with the intelligence necessary for VLAN segmentation. CMC Limited
  41. 41. VLAN Memberships VLANs are usually created by an administrator, who then assigns switch ports to each VLAN. Such a VLAN is called a static VLAN.Static VLANs Static VLANs are the usual way of creating VLANs, and they’re also the most secure.Dynamic VLANs A dynamic VLAN determines a node’s VLAN assignment automatically. CMC Limited
  42. 42. Configure VLANs on a SwitchYou can create up to 64 VLANs on a 1900 switch. Aseparate spanning-tree instance can be configured perVLAN.Assigning Switch Ports to VLANsYou can configure each port to be in a VLAN by using thevlan-membership command.You can only configure VLANs one port at a time. There isno command to assign more than one port to a VLAN at atime with the 1900 switch. CMC Limited
  43. 43. Configure VLANs on a Switch contd..VLAN BenefitThere are several benefits to using VLANs. To summarize,VLAN architecture benefits include: • Increased performance • Improved manageability • Network tuning and simplification of software configurations • Physical topology independence • Increased security options CMC Limited
  44. 44. Configure VLANs on a Switch contd..VLAN LimitationThere are a few limitations to using VLANs, some of themare as follows • Broadcast limitations • Device limitations • Port constraints CMC Limited
  45. 45. VLAN Trunk Protocol (VTP)The goal of VLAN Trunk Protocol (VTP) is to manage allconfigured VLANs across a switched internetwork and tomaintain consistency throughout that network.Following are the list of some of the benefits VTP has to offer: • Consistent VLAN configuration across all switches in the network. • Allowing VLANs to be trunked over mixed networks, like Ethernet to ATM LANE (Asynchronous Transfer Mode LAN emulation) or FDDI (Fiber Distributed Data Interface). • Accurate tracking and monitoring of VLANs. • Dynamic reporting of added VLANs to all switches • Plug-and-Play VLAN adding. CMC Limited
  46. 46. VLAN Trunk Protocol (VTP) contd..VTP ModeVTP-capable devices can be configured to operate in thefollowing three modes: • Server • Client • TransparentVTP Domain NameIn order to use VTP, you must assign a VTP domain nameto each switch. VTP information will remain only within thesame VLAN domain. CMC Limited
  47. 47. Configuring Trunk Ports The 1900 switch only runs the Dynamic Inter-Switch Link (DISL) encapsulation method. To configure trunking on a Fast Ethernet port, use the interface command trunk parameter.Clearing VLANs from Trunk Links All VLANs are configured on a trunked link unless cleared by an administrator. Use the clear trunk command if you don’t want a trunked link to carry VLAN information. CMC Limited
  48. 48. Configuring Trunk Ports contd..Verifying Trunk LinksTo verify your trunk ports, use the show trunk command.If you have more than one port trunking and want to seestatistics on only one trunk port, you can use the showtrunk port-number command. CMC Limited
  49. 49. VTP Configuration on Catalyst Switches To configure VTP, first configure the domain name you want to use. Once you configure the VTP information on a switch, you need to verify the configuration. CMC Limited
  50. 50. VTP Configuration on Catalyst Switches contd..Configuring the Domain When you create the VTP domain, you have the option to set the domain name, password, operating mode, and pruning capabilities of the switch.Adding to a VTP Domain You need to be careful when adding a new switch into an existing domain. If a switch is inserted into the domain and has incorrect VLAN information, the result could be a VTP database propagated throughout the internetwork with false information. CMC Limited
  51. 51. VTP Configuration on Catalyst Switches contd..VTP Pruning If you turn VTP pruning on in a VTP server, you turn it on for the whole domain as well. This will not send VTP broadcasts down a trunked link if no VLANs configured on this switch are present down the link. CMC Limited
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