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Transcript
SHRAVANI Introduction Switches are widely being used today by most of the business networks to connect multiple devices such as computers, printers and servers that are present within a particular boundary like a campus or building. The switch is responsible for enabling communication between the networking devices on a Local area network (LAN) so that they could efficiently talk to each other. The greater advantage of having them in the business is that they play a primary role in sharing the information and allocating the resources. The home networks made use of this little device before the routers popularized. In various types of networks the capability of switching exists. The widely known and the commonly used type are the Ethernet Switches. There are several models of these switches based on performance factors. They support a variety of connected devices and operate at the Data link layer of the OSI Model. Corporate switches can support from 32 to 128 connections, whereas the consumer grade switches can support 4 to 8 connections. Multiple switches could be connected to each other to provide larger device connectivity on the network. How they work? Hubs and Switches are look identical to each other and also occupy the same place as hubs, but their function varies. A switch unlike hub can inspect data in each packet as it is being received through the packet switching method instead of sending the same signal to every port. Through the packet examination it finds out the source and the destination details of every packet and forwards the packets accordingly to their destination. This process ultimately conserves a lot of network bandwidth and improves the performance when compared to hubs. The brief note points of what it does are given below. Once the data packet reaches a switch, it gathers all the information about the packet by inspecting it. The information includes the sources and the destination details of the packet. It maps the address to a table of addresses of the nodes on the network segments to forward it. If the network segments are same, then the packet is dropped or filtered. If they are different then it is forwarded to its specific network segment. SHRAVANI Only after mapping, that specific traffic is allowed to pass through it and forwarded to its network segment. The bad traffic is filtered out and stopped from spreading on the network. The basic functions of the switch are divided into three phases; Learning: This is process where the MAC addresses of the devices that are connected are obtained. Frame reaches the port of a switch The MAC address of the source is read by the switch from the frame MAC address compared with the CAM table that contains a list of MAC addresses. If MAC address entry is found on the CAM table, the incoming port and the port on the MAC table are compared by the switch If the port numbers do not match, the port number entry on the table is updated with the new port number. If MAC address not found on the CAM table, the address is added to the table along with the port number from the information on the frame. Forwarding: The process where the traffic is forwarded from one device to another device connected on different ports on the switch. From the learning process, the switch updates its CAM table and has all the required information extracted from the received Ethernet frame to forward the packet. The destination MAC address is also learnt as it is necessary for forwarding the data. The MAC address of the destination is required to find out the port number of the destination where the device is connected. If the MAC address of the destination is found on the table, the frame is forwarded through the port number corresponding to the address. If the MAC address is not found on the table, the frame is forwarded to all the ports on that switch leaving the source port. This process is called flooding. Lots of traffic is lost in this process of learning the destination MAC address. When the destination gets the frame, it sends back a reply frame to the device at the source. The MAC address from where the reply was sent is learnt by the switch and it adds that address to the MAC address table. SHRAVANI If the source and the destination MAC addresses are the same, the frame is dropped by the switch. This process is called filtering. This happens when a hub is connected to a port on the switch and when both the source and the destination devices are connected to that hub. Preventing L2 loops In real time LAN networking, to avoid the failure of the network redundant links are created in cases where a link fails. These redundant links could causing L2 looping and broadcast storms. This function on the switch prevents L2 looping and broadcast storms from happening. Some Important Points Packet Filtering and Forwarded packet regeneration make the switching technology more efficient. The network is split into separate independent collision domains. Packet regeneration allows more number of nodes to be used on the network and also reduces the collision rates overall on the network. In the switched network, every segment is a collision domain. This allows parallelism where half of computers connected to it can send data simultaneously. Shared networks have all the nodes on one collision domain that is shared. Switches could be installed very easily. They build a table of addresses on every segment, as they determine them from the packets that pass through them. Different types of networks could be connected through a switch. For example Ethernet and Fast Ethernet could be connected or the same type of networks could be connected through it. Fast Ethernet links which are high speed links are offered by switches today to link multiple switches or to add more bandwidth to get the traffic under control at the server. Such networks where multiple switches are linked through fast Ethernet links are called collapsed backbone networks. A full segment can be utilized for one node in order to gain higher speeds. Nodes to which there is high flow of traffic could be connected to a port that is dedicated for it on that switch. SHRAVANI Types of Ethernet Switches There are two categories of Ethernet Switches Modular Switches: These switches allow us to add modules into them to expand their usage and to make them more flexible for use on the networks where addresses keep changing. These expansion modules are specific to applications. Some examples of these modules are Network Analysis, Firewall, cooling fans etc. Cisco catalyst 4000 series and 6000 series are best examples for Modular Switches. Fixed Configuration switches: These switches have ports of fixed number and hence cannot be expanded. Cisco Catalyst 2000 series, 3000 series and Cisco 300/500 series are best examples of these kind of switches. The fixed configuration switches are broken down further into three categories; Unmanaged Switches: These switches are the best to deploy in real time as they are cost effective and function on switching and connectivity on Layer 2. They can be easily added to fit extra devices on the network. Some of these switches are capable of diagnosing the cable, prioritizing the traffic with the help of the QoS which is a default setting and also energy saving capability using EEE and PoE. From the name of the switch type we can see that these switches cannot be managed or modified. Unmanaged switches can be plugged in and used right away as they do not require any prior configurations to make them function. Best example of these kind of switches is Cisco 100 series. Smart switches: These Switches are also called lightly managed switches. They are very blurred and change very fast. They offer QoS, Security and Management but at low levels and hence they are less scalable when compared to the managed switches. These switches are the best alternatives to the managed switches as they are cost effective. They function perfectly when they are fit at the edges of large network which have managed switches used at their core. They also fit best for small networks or low complexity networks. They have a wide variety of capabilities. These devices have a specific interface for management. Earlier these devices were managed and configured through a web interface but now they are manageable through the command line interface as well. When compared to the managed switches, its SHRAVANI capabilities are lighter. But the management interface on the smart switch is easier and simpler to use when compared to the managed switches. The network could be segmented into workgroups by the creation of VLANs when using this switch category. The segmentation is allowed though the number of VLANs and nodes are low unlike what Managed switches offer. Certain levels of security are also offered by smart switches such as 802.1x endpoint authentication and Access control lists. This extent of security provided may not be as much provided by the Managed switch. Basic QoS is supported by the smart switches that help in user and application prioritization making them versatile. The best example of this switch category is the Cisco 200 series switches. Fully Managed Layer2 and Layer3 switches: These switches provide the most complex features as per their design. The features include the best experience of application, high security, effective network control and management, high scalability in fixed configuration switches. As a result of these features, they are mostly deployed in larger networks as access switches or in the small networks as core switches. These switches support both layer 2 switching and layer 3 Routing. When seen from the security point of view, these switches protect the data plane, where the user forwards the traffic , the control plane, where the traffic is sent from one device to another on the network to drive to the correct destination and the management plane, where the network or device is managed by the traffic itself. Services like storm control on networks, DoS protection and lots more. Dropping flexibly, limiting the rate, mirroring, traffic logging by L2, L3 addresses, port numbers of TCP/UDP, type of Ethernet, TCP flags or ICMP etc. Features are very rich in this switch category. They enable the switches to fight and protect themselves against the DoS attacks. Features include Dynamic inspection of ARP, DHCP IPv4 snooping and lots more. Other security features include private VLANs for securing user communities and isolation of the devices, secured management, Policing the control plane for protecting the switch of CPU AND wide support for 802.1x. These switches have tables of large size so that VLANs can be created in large number, MAC table size, ACL policies, IP routes etc. These are looked upon from the scalability point of view. To provide high availability of network and uptime, these switches use Virtual SHRAVANI Router Redundancy Protocol for supporting the Layer 3 redundancy. These switches also provide support for large number of “Link aggregation groups”, and protection for Layer 2 such as guards for Spanning tree root and BPDU. Optimization of the multicast traffic on LAN, Congestion avoidance of TCP, Limitation on traffic etc is the features of QoS. The best example of this switch category is Cisco 300 series and 500 series. Switches can also be chosen based on other options like; Speed Port Count POE vs Non POE Stackable vs Standalone Things to be considered when selecting a switch; Specifications like traffic flow details, data servers and storage servers should be on the top priority to select the switch. Future growth Performance Port speed of the switch Port density Rate of forwarding Link aggregation Power over Ethernet(PoE)