ccna zertifikat

ccna zertifikat.13.6 Authentication SummaryBridges have three main functions: learning, forwarding, and loop elimination. When performing the learn function, they add the source MAC address and associated bridge port to the port address table (CAM table). They perform flooding for traffic whose destination address is a multicast address, a broadcast address, or an unknown unicast address.STP is used to eliminate Layer 2 loops.STP uses BPDUs to learn about other neighboring switches. these BPDUs are multicast and are generated at 2-second intervals. When running STP, a ^root switch is elected - the switch with the smaller switch ID (bridge ID blush). The switch ID consists of the priority and the MAC address of the switch. Each switch selects a root port for travel to the root switch-the port with the lowest cumulative path overhead. Each segment has a designated port for forwarding traffic from and to that segment. this port is usually one of the ports on the switch with the lowest cumulative path overhead. There are five port states: blocking (lasts 20 seconds), listening (lasts 15 seconds), learning (lasts 15 seconds), forwarding, and disabled. portFast switches the port immediately to the forwarding state and should only be used for ports where the connected device is not a switch. pvst+ gives each VLAN an instance of STP, a protocol that is Cisco-specific, but which IEEEMSTP has standardized.RSTP reduces convergence time to just a few seconds, which is achieved by having the switch identify alternative root ports and alternate designated ports ,so that they can be used directly when topology changes occur. To enable RSTP-enabled PVST+, use the command spanning-tree mode rapid-pvstoEtherChannel bundles multiple Layer 2 connections between devices so that the STP appears to have only one logical port. This allows the load to be balanced between the ports contained in the channel. To create a channel, use PAgP or LACPo A channel can contain up to 8 interfaces.If CPU or port usage is high, it may mean that a Layer 2 loop exists. Typically, a protocol analyzer should be used to find if there are multiple copies of the same frame in the captured frame.13.7 Two-Minute SprintLayer 2 Redundancy . A campus network design contains three layers: the access, distribution, and core layers. . Redundancy in a Layer 2 network can lead to loops, which in turn can cause problems such as multiple copies of frames, broadcast storms, and failure to properly learn MAC addresses.Spanning Tree Protocol .STP is defined in 802. Id to eliminate loops in the network.. The switch with the lowest switch ID (priority and MAC address) is elected as the root switch. . Each switch picks out the best path to the root switch and the corresponding port is called the root port. Each network segment requires a switch port for accessing the rest of the network. this port is called the designated port.