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Repeaters, Switches and Routers

Repeaters, Switches and Routers. This presentation will focus on network hardware used to support Ethernet networks. Repeaters, Switches and Routers. Repeater:

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Repeaters, Switches and Routers

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  1. Repeaters, Switches and Routers • This presentation will focus on network hardware used to support Ethernet networks

  2. Repeaters, Switches and Routers • Repeater: • A Physical Layer device that regenerates digital signals, bringing them back to standard form, and transferring each bit from one LAN segment to another.

  3. Repeaters, Switches and Routers • Cisco Fasthub 100 series Repeater

  4. Repeaters, Switches and Routers • Repeater • This is the least complex and least expensive of the three devices • It operates on Layer 1 of the OSI model • Typically no configuration required • It deals with one bit at a time • It knows nothing about addresses

  5. Repeaters, Switches and Routers • Repeater • Any signal coming in on one port is sent out on all other ports • It has the lowest latency of any of these three devices • It has the least memory and processing power of any of these three devices

  6. Repeaters, Switches and Routers • Repeater • Usually people say Repeater when they mean Multiport Repeater • When someone refers to a Hub, they are usually referring to a Multiport Repeater • Although you can repeat any digital signal, these days people usually mean a UTP Ethernet repeater

  7. Repeaters, Switches and Routers • Repeater • Repeaters require no configuration, but can often be configured to support protocols like SNMP. • A true repeater can regenerate a signal from any media to any media, but it can’t change the data rate of the signal between ports

  8. Repeaters, Switches and Routers • Repeater • Devices on a network can’t detect when a repeater is being used on a network • Repeaters allow collisions to pass, therefore all devices connected to a repeater or series of repeaters are on the same collision domain.

  9. Repeaters, Switches and Routers • A repeater was originally installed when we wanted to extend the network beyond the maximum cable length allowed by 802.3. A repeater regenerated the signal allowing for a longer network.

  10. Repeaters, Switches and Routers

  11. Repeaters, Switches and Routers • Repeaters are rarely used in commercial installations any more. Switch prices have come down to be very competitive in price with repeaters, and they provide considerably improved functionality • Most repeaters that are sold are now used in a home network.

  12. Repeaters, Switches and Routers • A typical Bridge: • It is a Layer 2 device that understands Frames • Has only two ports • Learns the MAC address of each host by looking at the transmitted frames • No configuration is required • A bridge breaks up collision domains

  13. Repeaters, Switches and Routers • Bridge: • It will pass a broadcast, but will isolate unicast traffic, allowing separate simultaneous conversations on each side of the bridge • Bridges are often installed to improve the performance of a network with too high of a collision rate

  14. Repeaters, Switches and Routers • Bridge: • Bridges do more processing than a multiport repeater because they assemble Frames and do error detection and correction • The value of bridges can be defeated by a broadcast intensive Network Operating System

  15. Repeaters, Switches and Routers • Bridge: • Bridges were commonly selected to provide a transition from one media type to another, e.g. from coax to UTP • Repeaters can also provide that transition • However, with bridges, ports can run at differing data rates

  16. Repeaters, Switches and Routers • Bridge:

  17. Repeaters, Switches and Routers • Switch • A Multiport bridge is called a switch • It performs the same functions as a bridge • It is typically used within a LAN and requires no configuration. • It requires a lot of memory to buffer data as it comes in on each port

  18. Repeaters, Switches and Routers

  19. Repeaters, Switches and Routers • Switch • It has more latency than a repeater because of the data buffering requirement • The amount of RAM required is related to the number of hosts supported per port • The amount of RAM is also related to the switching method

  20. Repeaters, Switches and Routers • Switch • Switches typically use one of three selectable switching methods: • Cut Through • Fragment Free • Store and Forward

  21. Repeaters, Switches and Routers • Switch • Cut Through: A frame begins coming in through a port. As soon as the address of a frame is received and before the entire frame is received, the destination address is looked up in it’s address table and the frame is sent out.

  22. Repeaters, Switches and Routers • Switch • Cut Through: The frame is typically not yet completely received, nor is error detection and correction completed. It provides for extremely fast switching but often increases the number of errors, especially on a busy network • Errors take a heavy toll on the network

  23. Repeaters, Switches and Routers • Switch • Fragment Free: This allows the first 64 Bytes of the frame to be received. Since 64 bytes is the minimum size of an Ethernet packet, enough time has passed for all devices on the network to recognize there is traffic out there and a collision that would cause a fragment is less likely.

  24. Repeaters, Switches and Routers • Switch • Fragment Free: Error detection is only done on minimum size frames since the FCS field is not received by the time the other frames are switched. This technique is still a pretty low latency method of switching and it provides a significant improvement in numbers of errors over cut-through because many packets are only 64 bytes long.

  25. Repeaters, Switches and Routers • Switch • Store-and-forward: With this method the entire frame is received before it is forwarded on to the destination port. Error checking is completed, so errors are not forwarded. Latency, though, goes way up. This is the best choice for a very busy network. Can you understand why?

  26. Repeaters, Switches and Routers • Switch • Early on people recognized that switches could provide different data rates for different ports, effectively giving priority to one port over another.

  27. Repeaters, Switches and Routers • Cisco 2950 series Switches

  28. Repeaters, Switches and Routers • Cisco 4500 series Switches

  29. Repeaters, Switches and Routers • Switch

  30. Repeaters, Switches and Routers • Switch • We migrated from bridging LAN segments to putting a single host on each port, which is the preferred configuration today. • Repeaters, bridges and routers are almost absent from LANs now because of modern switches

  31. Repeaters, Switches and Routers • Switch • Spanning Tree Protocol: This allows a network engineer to include a redundant link, so if one link fails, another is already queued up to carry the data. • Without some way of dealing with redundant links (sometimes called loops), broadcast storms occur

  32. Repeaters, Switches and Routers • Switch • A broadcast storm occurs when a broadcast goes around a loop and enters a single switch from two different segments. In that case, switches keep forwarding frames out more than one port, so they are forwarding frames to themselves.

  33. Repeaters, Switches and Routers • Switch • Spanning Tree is a protocol that is used strictly between switches that allow them to negotiate a root bridge, and then temporarily turn off (block) one or more port to break up the loop. If a network link failure occurs, the blocked port is reactivated.

  34. Repeaters, Switches and Routers • Switch • The organizer of this action is the “root” switch, which stays in communication with all other switches. • The “root” switch is elected by comparing the priority settings of each switch. Conflicts are resolved by comparing MAC addresses. The lowest number wins.

  35. Repeaters, Switches and Routers • Switch • In the event of multiple connections to the root switch, ports are assigned a cost figure. (See table 2.1). The lowest cost is associated with the highest data rate, and it becomes the port used. • Blocking and port selection decisions are made from the perspective of the root switch.

  36. Repeaters, Switches and Routers • Switch • Many switch manufacturers recognize the problems a loop can cause but are unwilling to implement STP because of its complexity and delay (50 seconds for convergence). Instead they isolate links that cause a loop.

  37. Repeaters, Switches and Routers • Router • Layer 3 devices • Routers are put at the edge of a network • They define the end of a network • They are the most common devices used to provide access to a WAN

  38. Repeaters, Switches and Routers • Router • They can help you logically segment your network • They block broadcasts • Routers are typically much more expensive than repeaters or switches • Routers typically cause much higher latencies than switches

  39. Repeaters, Switches and Routers • Router • They buffer the complete packet before making a forwarding decision • Error detection occurs on the header • Traditionally used to interconnect two dissimilar LANs (eg ATM and Token Ring). More recently have lost this role to Switches.

  40. Repeaters, Switches and Routers • Router • A complex routing protocol is employed to accommodate multiple links between routers • They are much more software based than switches • Routers can be configured to block or pass specific protocols, provide NAT, and other functions

  41. Repeaters, Switches and Routers • Router • These devices require a much greater processing capability • You typically (Cisco) pay for each protocol that is included • Each router manufacturer has its own unique operating system

  42. Repeaters, Switches and Routers • SoHo Router

  43. Repeaters, Switches and Routers • Cisco 2600 series Routers

  44. Repeaters, Switches and Routers • Cisco 12000 series Routers

  45. Repeaters, Switches and Routers

  46. Repeaters, Switches and Routers • Router • Typically must be manually configured • It works harder and transfers data more slowly than either repeaters or switches • Routers used to be employed within a LAN but are now rarely used that way because of the impact on traffic

  47. Repeaters, Switches and Routers • Wireless

  48. Repeaters, Switches and Routers • Where are the Bus cables? • Coaxial bus cables are rarely used in modern LAN installations • All of the high speed LAN standards are designed for UTP and Fiber, not on bus cables. • Star and Tree structures are used almost exclusively in LANs

  49. Repeaters, Switches and Routers • Where are the fiber interfaces? • Where are the UTP interfaces? • Where are the WAN interfaces? • Where are the console interfaces?

  50. Repeaters, Switches and Routers • Modern hardware can be purchased with whatever interface you choose to pay for. • Repeaters and switches come with UTP interfaces on most ports • Some hardware has modular ports, allowing for some flexibility, but it comes at a price

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