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CCNA 2 – ch1

* Switch L2 de çalışır, mac adreslerine göre iş yapar

* Switch gelen frame lerin source mac address alanına bakarak mac address table (cam table) oluşturur.

* Switch gelen frame lerin destination mac address alanına bakarak switching yapar.

* Switch gelen frame deki destination mac address ini bilmiyorsa flooding (gelen port haricindeki tüm aktif portlara anahtarlar) yapar.

* Switch e gelen frame in destination mac address i broadcast ise (FFFF.FFFF.FFFF) flooding yapar.

* Switch filtering yapar.

* Switch aging yapar.

* Switch ler switching operasyonunu asic (application-specific-integrated circuits) ler ile yapar.

Creating a borderless switched network requires that sound network design principles are used to ensure maximum availability, flexibility, security, and manageability. The borderless switched network must deliver on current requirements and future required services and technologies. Borderless switched network design guidelines are built upon the following principles:

  • Hierarchical - Facilitates understanding the role of each device at every tier, simplifies deployment, operation, and management, and reduces fault domains at every tier
  • Modularity - Allows seamless network expansion and integrated service enablement on an on-demand basis
  • Resiliency - Satisfies user expectations for keeping the network always on
  • Flexibility - Allows intelligent traffic load sharing by using all network resources

Access Layer

The access layer represents the network edge, where traffic enters or exits the campus network. Traditionally, the primary function of an access layer switch is to provide network access to the user. Access layer switches connect to distribution layer switches, which implement network foundation technologies such as routing, quality of service, and security.

Distribution Layer

The distribution layer interfaces between the access layer and the core layer to provide many important functions, including:

  • Aggregating large-scale wiring closet networks
  • Aggregating Layer 2 broadcast domains and Layer 3 routing boundaries
  • Providing intelligent switching, routing, and network access policy functions to access the rest of the network
  • Providing high availability through redundant distribution layer switches to the end-user and equal cost paths to the core
  • Providing differentiated services to various classes of service applications at the edge of network

Core Layer

The core layer is the network backbone. It connects several layers of the campus network. The core layer serves as the aggregator for all of the other campus blocks and ties the campus together with the rest of the network. The primary purpose of the core layer is to provide fault isolation and high-speed backbone connectivity.

Fixed Configuration Switches

Fixed configuration switches do not support features or options beyond those that originally came with the switch. The particular model determines the features and options available. For example, a 24-port gigabit fixed switch cannot support additional ports.

Modular Configuration Switches

Modular configuration switches offer more flexibility in their configuration. Modular configuration switches typically come with different sized chassis that allow for the installation of different numbers of modular line cards. The line cards actually contain the ports. The line card fits into the switch chassis the way that expansion cards fit into a PC. The larger the chassis, the more modules it can support. There can be many different chassis sizes to choose from. A modular switch with a 24-port line card supports an additional 24 port line card, to bring the total number of ports up to 48.

Stackable Configuration Switches

Stackable configuration switches can be interconnected using a special cable that provides high-bandwidth throughput between the switches. Cisco StackWise technology allows the interconnection of up to nine switches. Switches can be stacked one on top of the other with cables connecting the switches in a daisy chain fashion. The stacked switches effectively operate as a single larger switch. Stackable switches are desirable where fault tolerance and bandwidth availability are critical and a modular switch is too costly to implement. Using cross-connected connections, the network can recover quickly if a single switch fails. Stackable switches use a special port for interconnections. Many Cisco stackable switches also support StackPower technology, which enables power sharing among stack members.

Store-and-forward switching has two primary characteristics that distinguish it from cut-through: error checking and automatic buffering.

Rapid Frame Forwarding  a switch using the cut-through method can make a forwarding decision as soon as it has looked up the destination MAC address of the frame in its MAC address table. The switch does not have to wait for the rest of the frame to enter the ingress port before making its forwarding decision.

Fragment Free switching is a modified form of cut-through switching in which the switch waits for the collision window (64 bytes) to pass before forwarding the frame. This means each frame will be checked into the data field to make sure no fragmentation has occurred. Fragment free mode provides better error checking than cut-through, with practically no increase in latency.

* Although switches filter most frames based on MAC addresses, they do not filter broadcast frames. For other switches on the LAN to receive broadcast frames, switches must flood these frames out all ports. A collection of interconnected switches forms a single broadcast domain. Only a network layer device, such as a router, can divide a Layer 2 broadcast domain. Routers are used to segment both collision and broadcast domains. When a switch receives a broadcast frame, it forwards the frame out each of its ports, except the ingress port where the broadcast frame was received.