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Transcript
Repeaters, Switches and Routers This presentation will focus on network hardware used to support Ethernet networks 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. Repeaters, Switches and Routers Cisco Fasthub 100 series Repeater 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 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 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 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 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. 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. Repeaters, Switches and Routers 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. 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 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 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 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 Repeaters, Switches and Routers Bridge: 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 Repeaters, Switches and Routers 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 Repeaters, Switches and Routers Switch Switches typically use one of three selectable switching methods: Cut Through Fragment Free Store and Forward 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. 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 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. 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 cutthrough because many packets are only 64 bytes long. 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? 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. Repeaters, Switches and Routers Cisco 2950 series Switches Repeaters, Switches and Routers Cisco 4500 series Switches Switch Ethernet Repeaters, Switches and Routers 7x 8x 9x 1x 2x 3x 10x 11x 12x 7x 8x 9x 4x 1x 2x 3x 10x 11x 12x C 7 8 9 101112 A 123456 A 5x 10 Mbps 6x B 4x 5x 6x Switch 10 Mbps 100 Mbps 10 Mbps Server 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 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 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. 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. 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. 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. 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. 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 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 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. 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 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 Repeaters, Switches and Routers SoHo Router Repeaters, Switches and Routers Cisco 2600 series Routers Repeaters, Switches and Routers Cisco 12000 series Routers Repeaters, Switches and Routers WAN Router Router Switch Switch Workstation Workstation Workstation Workstation Workstation Workstation 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 Repeaters, Switches and Routers Wireless 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 Repeaters, Switches and Routers Where are the fiber interfaces? Where are the UTP interfaces? Where are the WAN interfaces? Where are the console interfaces? 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 Repeaters, Switches and Routers Routers are most likely to have the most flexibility with regard to interface. They will have multiple LANs and WANs Switches often have configurations that provide for a higher speed uplink port. Repeaters, Switches and Routers VLAN: Virtual Local Area Network Defines Broadcast Domains Dynamically configured By protocol By IP address By authenticated login Port configured