Cisco Certifications Tutorials

32 http:\\ciscocertifications.info *Keypoints: Be sure to know the difference between full and half duplex communication. LAN Segmentation Bridges segment LAN's by learning the MAC address of the nodes on each directly connected interface. This helps segment LAN's because the Bridge looks up the destination MAC address in its address table and forwards the frame to the correct interface. Bridges act to increase the number of collision domains. The downside is that frames with unrecognized MAC addresses are forwarded to every interface. Bridges work at the data-link layer or layer 2. Routers Can be used to segment LAN's via routing between two or more Ethernet interfaces. Broadcasts will be filtered and the packets will be routed based upon the destination network address (IP or IPX). Sepa- rates broadcasts and possibly protocols. Each segment is a broadcast domain of it's own and does not pass broadcasts to the adjacent segments. Routers can connect networks that use different media and it works at the network layer or layer 3. Switches Are advanced multiport bridges that can either segment LAN's or provide total end to end non- contentious bandwidth to clients. They support Full Duplex. VLAN's can be used. Switches work on the MAC address (Data Link Address) in the same way as Bridges but they switch at the hardware level (Wire Speed), whereas a bridge uses software. As a result, switches are much faster layer 2 devices. Switches use either store-and-forward switching, cut-through switching, or a hybrid version for LAN switching (forwarding) traffic. Repeaters & Hubs Are both devices that operate at the physical layer of the OSI model. They simply pass data without performing any type of address recognition functionality. *Keypoints: Routers use IP addresses to forward packets. Know which layers of the OSI model the above devices operate in. Bridges increase the number of collision domains, thus reducing the number of collisions. Bridges lookup MAC addresses in their address table and forwards the data toward the destination device. Switches are the devices most used for micro-segmentation. Know that switches create separate collision domains, but only a single broadcast domain. Know that routers provide for separate broadcast domains Know that LAN segmentation is good because it provides smaller collision domains. Full-duplex Ethernet is collision free. Know that a "backoff" is the retransmission delay that is enforced when a collision occurs. Know that the "BASE" in 10BaseT refers to the signaling type (Baseband). Know that routers route based upon the destination network address of an incoming packet. Know that replacing a hub with a switch will reduce network congestion. Know that MAC address sent during an Ethernet broadcast is "FF-FF-FF-FF-FF-FF. Know that switches are the most common layer 2 devise (except for bridges). Know that a full-duplex Ethernet requires point-to-point connection when only 2 nodes are present. Know that full duplex Ethernet takes advantage of UTP by using 1 pair of wires for transmission and the other for reception. Know that bridges will not isolate broadcasts or multicast packets, and that these packets will cause floods.