* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Document
Survey
Document related concepts
Recursive InterNetwork Architecture (RINA) wikipedia , lookup
Computer network wikipedia , lookup
Airborne Networking wikipedia , lookup
Parallel port wikipedia , lookup
Wake-on-LAN wikipedia , lookup
IEEE 802.1aq wikipedia , lookup
Multiprotocol Label Switching wikipedia , lookup
Deep packet inspection wikipedia , lookup
Asynchronous Transfer Mode wikipedia , lookup
Network tap wikipedia , lookup
Cracking of wireless networks wikipedia , lookup
Packet switching wikipedia , lookup
Transcript
Chapter 5 Switching Introduction • Look at: – Bridges and Bridging(5.1) – Switches and Switching(5.2) – Spanning Tree Algorithm(5.3) – Virtual Local Area Networks (VLANs)(5.4) – Integrating Switches(5.5) Introduction • Moving electronic signals from one interface to another is the term used to describe switching • Ethernet networks started as a single segment bus topology with all clients able to receive the electronic signals of all other clients on their network Bridges and Bridging • A bridge operates by simply plugging it into the wall and connecting network devices to it • Bridging can isolate groups of network devices by segmenting the wire signals of one group from another group • Each of the separate groups is referred to as a collision domain • Fewer devices competing per network segment mean better communication Bridges and Bridging • There are several different implementations of bridging: – Transparent bridging – Source route bridging – Translational bridging • Each has a specific purpose in controlling traffic flows and collisions Bridges and Bridging • In transparent bridging, the network devices are unaware of the presence of the bridge • The bridge forwards traffic based on a first-in, first-out (FIFO) basis and combines the transmissions allowing multiple clients to communicate with the Server • Network transmissions take a small amount of time, and the bridge must be fast enough to keep up Bridges and Bridging • Source route bridging (SRB) is designed for use with Token Ring networks • In Token Ring networks, rings and bridges have an assigned numeric value • The client determines the best path through the Layer 2 network • The default behavior is to use the path identified in the first response received Bridges and Bridging • Translational bridging contains a mixture of Ethernet and Token Ring clients • Very few standards exist for translational bridging, and implementations vary between vendors • Some translational bridging implementations may not work between vendors • It’s important to research compatibility if you plan on implementing translational bridging Switches and Switching • Switching offers the following improvements over bridging: – Higher port density – Faster packet processing capabilities – Quality of service (QoS) capabilities – Use of virtual LAN (VLAN) technology • Each port is a single bridging device creating its own collision domain Switches and Switching • Switches achieve faster packet processing capabilities than bridges in a number of different ways: – Application-specific integrated circuits – Better CPUs – Cut-through switching – Fragment-free switching Switches and Switching • Circuit switching is the oldest form of switching • It establishes calls over the most efficient route available at the time • It can be wasteful compared to other types of communication • It is wasteful because the circuit remains active even if the end stations are not currently transmitting Switches and Switching • Examples of circuit-switched networks include: – Asynchronous Transfer Mode (ATM) – Integrated Services Digital Network (ISDN) – Leased digital line – T-1 – Analog dial-up line Switches and Switching • Types of switching include: – Time-division which is the switching of time-division multiplexed (TDM) channels by shifting bits between time slots in a TDM frame – Space-division in which single transmission-path routing is accomplished using a switch to physically separate a set of matrix contacts or cross-points Switches and Switching • Types of switching include: – Time-space division which precedes each input trunk in a crossbar with a TSI, and delays samples so that they arrive at the right time for the space-division switch’s schedule – Time-space-time division is where data passes through a space switch to create circuits for TDM outlets Switches and Switching • Packet switching is implemented by protocols that rearrange messages into packets before sending them • Each packet is then transmitted individually • Because packets are send via different routes, they may not arrive in the order in which they were originally sent • Technologies such as Cellular Digital Packet Data and Voice over IP is currently implementing voice communication using packet switching Switches and Switching • In packet switching protocols, a port is represented by a value between 1 and 65535 • The port number indicates the type of packet • Port mapping, or port address translation is a process where packets arriving for a particular socket can be translated and redirected to a different socket • Port mapping is necessary only for incoming transmissions, not for returning traffic Switches and Switching • Blocking occurs when a network is unable to connect stations to complete a circuit • In packet switching, blocking is caused by congestion • Congestion management is used to help ensure that the blocked packet is not lost • Congestion management is implemented using buffers or queues Switches and Switching • Asynchronous transfer mode (ATM) is a highspeed, connection orientated packet switching technique • It uses short, fixed-length packets called cells • ATM is connection oriented • The switching elements have pre-defined routing tables to minimize the complexity of single switch routing Switches and Switching • Switching fabric is the combination of hardware and software that transfers data coming into a node to the appropriate port on the next node • The bandwidth of a switching fabric is defined by its data width in bits and the speed at which it can transmit these bits • Switching fabric includes data buffers and shared memory Switches and Switching • A crossbar switch is a device that directly switches data between an input port and an output port without sharing a bus with any other data • Crossbar topology is similar to bus topology • There is only one path that all devices share • A crossbar switch environment offers more flexibility and greater scalability Switches and Switching • A broadcast connection is when a device simultaneously sends data to more than one receiving device • A broadcast connection in a non-blocking multistage network that has an input port connected simultaneously to several unused output ports • The network must be non-blocking for broadcast assignments Switches and Switching • A switching element is the basic building block of a switch • Switching fabric consists of switching elements that facilitate a particular switching mechanism • When a large number of switching elements are connected together in a network, this is a multistage interconnection network (MIN) Spanning Tree Algorithm • The Spanning Tree Algorithm (STA) was created to overcome the weakness inherent in bridges • This weakness is the flooding behavior of broadcast, multicast and unknown traffic types • Problems occur with broadcasts when you configure two or more bridges in a loop Spanning Tree Algorithm • By interconnecting multiple switches with redundant paths, you overcome problems with faulty cables or port failures • Another less well-known side effect of a loop is the corruption of the forwarding tables on all the switches • It would take very little time before Layer 2 broadcast loops completely destroy the functionality of a network Spanning Tree Algorithm • The Spanning Tree Protocol (STP) prevents bridging loops by identifying a preferred path through a series of looped bridges • Administrators can provide redundancy and fault-tolerance by wiring a loop, and then using STP turn off ports that would cause loops to occur • If a primary link fails, STP will reactivate the back-up port allowing normal operation of the network to continue Spanning Tree Algorithm • The STP process is accomplished by: – Election of a root bridge – Each bridge, when first turned on, begins the election process by sending a packet called a bridge protocol data unit (BPDU) – Each bridge believes itself to be the root until it receives a BPDU with a lower root bridge ID Spanning Tree Algorithm • The STP process is accomplished by: – Identification of a root port – Once the root bridge is determined, each non-root bridge finds the best path to the root using path cost – Path cost is a numeric value that bridges use to determine the preference of a given path. It is derived by taking 1000 MBps and dividing it by the speed of the link Spanning Tree Algorithm • The STP process is accomplished by: – Identification of a designated port – After the switches determine the root bridge and the best path to the root, the designated port is determined – When this step finishes, the loop is broken because one of the switches is blocking traffic on one of it’s ports Spanning Tree Algorithm • The switch continues to receive traffic on the port and evaluates each frame • All user traffic is filtered including unicasts, broadcasts, and multicasts frames • Anytime a new switch is plugged in, the process of determining the root bridge occurs Spanning Tree Algorithm • Most bridges and switches go through the following phases when activating ports to determine which system is the root bridge and which ports are active or disabled – Blocking – Listening – Learning – Forwarding Virtual Local Area Networks • Prior to the concept of VLANs the only way for administrators to block broadcast traffic was to implement a router • VLANs represent a solution allowing administrators to group ports on their switches so that broadcast traffic is only passed among ports within the group • Once a VLAN is established the ports will only flood broadcast traffic to their own members Virtual Local Area Networks • Once the VLAN is created, it is necessary to have a Layer 3 router • The clients on separate VLANs will no longer communicate with each other • The network devices can no longer discover each other by using ARP broadcasts Virtual Local Area Networks • The basic process of creating a VLAN involves tagging the inbound packet with a VLAN ID • Tagging is accomplished in one of two ways: – Frame insertion – Frame encapsulation Virtual Local Area Networks • Frame insertion involves inserting a small identifier into the frame as it is received at the switch’s port • In Frame encapsulation, the entire frame is simply encapsulated inside a VLAN ID header and checksum • Encapsulation is still a proprietary method of VLAN tagging but is gaining in popularity • It is fast at frame insertion and less prone to damaging the underlying frame Virtual Local Area Networks • VLAN trunking uses the VLAN concept and applies it to more than one switch • The solution for routing frames is trunking or making one port forward traffic for all VLANs • Doing so cuts port usage down considerably • While VLANs appear complex at first, they offer a great deal of flexibility for administrators Virtual Local Area Networks • If a particular device needs to be moved from one broadcast domain to another, only the port configuration on the switch needs to be changed, not the physical location of the device • Fewer ports are used on the routers, saving money and configuration time Integrating Switches • Integrating hubs and switches provide a migration path as networks are upgraded from hub environments to switching topologies • This can be done by connecting a crossover network cable from one of the hub ports into a switch port • If the hub or switch includes a crossover port then you use a regular networking cable Integrating Switches • All ports on a hub are in the same broadcast and collision domain • All ports on a switch are in the same broadcast domain but each port is its own collision domain unless VLANs are used • Connect your servers and other high traffic workstations directly to a switch so that they are free from collisions Integrating Switches • Some switches can allow you to add functions such as: – Packet filtering – Encryption – Auditing/Accounting – Tunneling – Routing Integrating Switches • By adding these directly to the switch, frames are copied into the memory of the switch once and then forwarded on to the next destination without further copying • This allows a switch to route frames at wire speed • An additional side benefit of integrating switches with routing technology is the simplification of network design