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| Why segment a LAN? | By using segments in a network, less users/devices are sharing the same 10Mbps when communicating to one another within the segment. Each segment is considered its own collision domain. |
| Purpose of LAN switching | The purpose for using LAN switching is to ease bandwidth shortages and network bottlenecks such as between several PCs and a remote file server. A LAN switch is a very high-speed multiport bridge with one port for each node or segment of the LAN. A switch segments a LAN into microsegments creating collision free domains from one larger collision domain. |
| How does a switch learn device addresses? | reading the source address of each packet transmitted & noting the port where the frame was heard. The switch then adds this information to its forwarding database. Addresses are learned dynamically. This means that as new addresses are read they are learned and stored in content addressable memory (CAM) for future use. |
| Symmetric switching | one way of characterizing a LAN switch according to the bandwidth allocated to each port on the switch. A symmetric switch provides switched connections between ports with the same bandwidth, such as all 10 Mbps or all 100 Mbps ports. |
| Asymmetric switching | provides switched connections between ports of unlike bandwidth, such as a combination of 10 Mbps and 100 Mbps ports. This type of switching is also called 10/100 switching. |
| Store and Forward | the entire frame is received before any forwarding takes place. The destination and/or the source addresses are read and filters are applied before the frame is forwarded. Latency occurs while the frame is being received; the latency is greater with larger frames because the entire frame takes longer to read. Error detection is high because of the time available to the switch to check for errors while waiting for the entire frame to be received. |
| Cut-through (Fast Forward) | the switch reads the destination MAC address and begins forwarding the frame before it is completely received. This mode decreases the latency of the transmission and has poor error detection. |
| VLANs | logically segment the physical LAN infrastructure into different subnets (broadcast domains for Ethernet) so that broadcast frames are switched only between ports within the same VLAN. |
| Frame filtering | a technique that examines particular information about each frame. The concept of frame filtering is very similar to that commonly used by routers. A filtering table is developed for each switch, which provides a high level of administrative control because it can examine many attributes of each frame. |
| Frame identification (frame tagging) | uniquely assigns a user-defined ID to each frame. This technique was chosen by the IEEE standards group because of its scalability. |
| Port-Centric virtual LANs | VLAN membership by port maximizes forwarding performance because: 1) Users are assigned by port; 2) VLANs are easily administered 3) Security between VLANs is maximized 4) Packets do not "leak" into other domains 5) VLANs and VLAN membership are easily controlled across network |
| Static VLANs | ports on a switch that you statically assign to a VLAN. These ports maintain their assigned VLAN configurations until you change them. |
| Dynamic VLANs | ports on a switch that can automatically determine their VLAN assignments. Most switch manufacturers use intelligent management software. Dynamic VLAN functions are based on MAC addresses, logical addressing, or protocol type of the data packets. |
| LAN Design goals | Functionality; Scalability; Adaptability & Manageability |
| 3 steps for LAN design | Analyze requirements; Develop LAN structure (topology) and setup addressing and routing |
| Layer 1 - Physical Layer Design | Includes wire media type such as CAT5 UTP and fiber-optic cable along with TIA/EIA-568-A Standard for layout and connection of wiring schemes. Design Goal: Build this layer of the OSI model with speed and expansion capabilities. |
| Layer 2 - Data Link Layer Design | Includes selection of Layer 2 devices such as bridges or LAN switches used to interconnect the Layer 1 media to a LAN segment. Devices at this layer will determine the size of the collision and broadcast domains. Design Goals: 1) Create a concentration point within the MDFs or IDFs where end hosts can be grouped at Layer 1 to form a physical LAN segment. 2) Install LAN switching devices that use microsegmentation in order to reduce the collision domain size. 3) Create a point (at Layer 2) of the topology where users can be grouped into virtual workgroups (VLANs) and unique broadcast domains. |
| Server placement | If servers are to be distributed around the network topology according to function, the networks Layer 2 and 3 must be designed to accommodate this. Within the MDF and IDFs, the Layer 2 LAN switches must have high speed (100Mbps) ports allocated for these servers. |
| Dynamic routing | relies on a routing protocol to share knowledge. A routing protocol defines the set of rules used by a router when it communicates with neighboring routers. |
| routing algorithm | When a routing algorithm updates the routing table, its primary objective is to determine the best information to include in the table. Each routing algorithm interprets "best" in its own way. The algorithm generates a number - called the metric value - for each path through the network. Typically, the smaller the metric number, the better the path. |
| Bandwidth metric | Data capacity of a link. For instance, normally, a 10-Mbps Ethernet link is preferable to a 64-kbps leased line |
| Delay metric | Length of time required to move a packet from source to destination. |
| Load metric | Amount of activity on a network resource such as a router or link. |
| Reliability metric | Usually refers to the error rate of each network link. |
| Hop count | Number of routers a packet must pass through. |
| Tick | Delay on a data link using IBM PC clock ticks (approximately 55 milliseconds). |
| Cost metric | Arbitrary value, usually based on bandwidth, dollar expense, or other measurement, that is assigned by a network administrator. |
| distance vector | The distance vector routing approach determines the direction (vector) and distance to any link in the internetwork. |
| link-state | The link-state (also called shortest path first) approach re-creates the exact topology of the entire internetwork (or at least the portion in which the router is situated). |
| Convergence | The knowledgebase needs to reflect an accurate and consistent view of the new topology. Convergence occurs when all routers in an internet are operating with the same knowledge (i.e. all routers have the same information on all the paths in the network). |
| Interior Routing Protocols | RIP; IGRP; EIGRP; OSPF |
| IGRP | a distance vector routing protocol developed by Cisco. IGRP sends routing updates at 90-second intervals that advertise networks for a particular autonomous system. |
| Standard access lists | 1) Standard access lists for IP check the source address of packets that could be routed. The result permits or denies output for an entire protocol suite, based on the network/subnet/host address. 2) For example, packets coming in E0 are checked for address and protocol. If permitted, the packets are routed through S0. 3) If the packets are denied by the standard access list, all these packets for the given category are dropped. |
| Extended access lists | 1) Extended access lists check for both source and destination packet addresses. They also can check for specific protocols, port numbers, and other parameters. This allows administrators more flexibility to describe what checking the access list will do. Packets can be permitted or denied output based on where the packet originated and on its destination. 2) The extended access list also permits or denies with more granularity. For example, it can allow electronic mail traffic from E0 to specific S0 destinations, while denying remote logins or file transfers. |
| wildcard mask bits | ยท A wildcard mask bit 0 means "check the corresponding bit value." A wildcard mask bit 1 means "do not check (ignore) that corresponding bit value." |
| the wildcard any | The administrator can use the abbreviation any to communicate this same test condition to Cisco IOS access list software. Instead of typing 0.0.0.0 255.255.255.255, the administrator can use the word any by itself as the keyword. |
