Cisco Certified Network Associate
If the network type of an interface is broadcast, the default OSPF priority is 1. When OSPF priorities are the same, the OSPF election for DR is decided on the router ID. The highest router ID is selected.
A value of 0 prevents that router from being elected.
- The access layer provides users in workgroups access to the network.
- The distribution layer provides policy-based connectivity.
- The core layer provides optimal transport between sites. The core layer is often referred to as the backbone.
- Functionality - The network must work. The network must allow users to meet their job requirements. The network must provide user-to-user and user-to-application connectivity with reasonable speed and reliability.
- Scalability - The network must be able to grow. The initial design should grow without any major changes to the overall design.
- Adaptability - The network must be designed with a vision toward future technologies. The network should not include elements that would limit implementation of new technologies as they become available.
- Manageability - The network should be designed to facilitate network monitoring and management to ensure continuous stability of operation
Layer 2 switching looks at a destination MAC address
The switching table is contained in Content Addressable Memory (CAM)
The main features of Ethernet switches are:
- Isolate traffic among segments
- Achieve greater amount of bandwidth per user by creating smaller collision domains
- Cut-through - A switch that performs cut-through switching only reads the destination address when receiving the frame. The switch begins to forward the frame before the entire frame arrives. This mode decreases the latency of the transmission, but has poor error detection. There are two forms of cut-through switching:
1. Fast-forward switching - This type of switching offers the lowest level of latency by immediately forwarding a packet after receiving the destination address. Latency is measured from the first bit received to the first bit transmitted, or first in first out (FIFO). This mode has poor LAN switching error detection.
2. Fragment-free switching - This type of switching filters out collision fragments, with are the majority of packet errors, before forwarding begins. Usually, collision fragments are smaller than 64 bytes. Fragment-free switching waits until the received packet has been determined not to be a collision fragment before forwarding the packet. Latency is also measured as FIFO.
- Store-and-forward - The entire frame is received before any forwarding takes place. The destination and source addresses are read and filters are applied before the frame is forwarded. Latency occurs while the frame is being received. Latency is greater with larger frames because the entire frame must be received before the switching process begins. The switch has time available to check for errors, which allows more error detection.
- Adaptive cut-through - This transmission mode is a hybrid mode that is a combination of cut-through and store-and-forward. In this mode, the switch uses cut-through until it detects a given number of errors. Once the error threshold is reached, the switch changes to store-and-forward mode.
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