CCNA v5.0 modul 2 Chapter: 1 - Introduction to Switched Networks

Switches function provides: Quality service, video y video data transfer and security

11.    LAN Design

 1.1 Converged Networks

Information must be available at any time, and on any device.

Elements of converged network are: voice systems, IP phones, voice gateways, video support, and video conferencing. Including data services.

A converged network with collaboration support may include features such as the following:     

-Call control  Telephone call processing, caller ID, call transfer, hold, and conference     

-Voice messaging   Voicemail     

-Mobility Receive important calls wherever you are     

-Automated attendant Serve customers faster by routing calls directly to the right department or individual

The benefits of transitioning to the converged network are that there is just one physical network to install and manage.  Affordability for small and medium businesses

1.2 Borderless Switchs Networks

Creating a borderless switched network requires that sound network design principles are used to ensure maximum availability, flexibility, security, and manageability.

The Cisco Borderless Network is built on an infrastructure of scalable and resilient hardware and software. It enables different elements, from access switches to wireless access points to work together and allow users to access resources from any place at any time, providing optimization, scalability, and security to collaboration and virtualization.

1.3 Hierarchy in the Borderless Switched Network

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

Critical layer are: access, distribution and core.

Access Layer

Traffic enters or exits, is the edge of the network.

Function: providing access to user

Access layer switches connect to distribution layer switches, which implement network foundation technologies such as routing, quality of service, and security.

To meet network application and end-user demand, the next-generation switching platforms now provide more converged, integrated, and intelligent services to various types of endpoints at the network edge.

With more intelligence in the access layer switches we allow application to operate on the net more efficiently and securely.

Distribution Layer (between access and core have more functions )

- 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.

Primary purpose: provide fault isolation (aislamiento de fallas) and high-speed backbone connectivity

To build a simplified, scalable, cost-effective, and efficient physical cable layout design, the recommendation is to build an extended-star physical network topology from a centralized building location to all other buildings on the same campus.

1.4 Role of the switched network

Now a day a switch is not only a flat layer 2 but allow more flexibility, traffic management, and additional features as:

-       Quality of Service

-       Additional security

-       Support for wireless networking and connectivity.

Type of switches are: Fixed configuration,  Modular,  and stackable

Cisco StackWise technology allows to interconnect up to 9 switches and operate as single layer. There are desirable where fault tolerance and bandwidth technology are critical. Modular switch is too costly to implement. Using cross-connected connections, the network can recover quickly if a single switch fails.

Special port for interconnecting and may support StackPower technology, witch enables power sharing among the stack members.

Consideration for selecting switch equipment: cost, Port density, Power, Reliability, Port Speed, Frame buffers, and scalability.

1.5 Switched environment

Fundamental concept of switching refers to a device making a decision based on two criteria:

-       Ingress port

-       Destination address

Only one master switching  table with a strict association between address and ports.

Depending of the ingress port the egress (exit) port is always the same. Cisco LAN switches forward Ethernet frames based on the destination MAC address of the frame.

A switch is an (ASIC) Application Specific Integrated Circuit.

A switch populates the MAC address table based on source MAC addresses.

In  multiple interconnected switches, the MAC address table contains multiple MAC addresses for a single port .

ASICs reduce the packet-handling time within the device, and allow the device to handle an increased number of ports without degrading performance.

Switch forwarding methods:

-       Store-and-forward: forwarding decision on a frame after it has received the entire frame and then checked the frame for errors.

Primary characteristics:  error checking (if CRC NOK drop the frame)  and automatic forwarding (flexibility to support any mix of Ethernet speeds)

-       Cut-through: begins the forwarding process after the destination MAC address of an incoming frame (first 14 bytes) and the egress port has been determined.

·      Switch may forward invalid frames because no FCS check is performed.

·      start forwarding a frame earlier

Characteristics:

             Rapid Frame Forwarding

             The switch does not have to wait for the rest of the frame to enter the ingress port before making its

             forwarding decision. Today MAC controllers and ASICs can quickly decide whether it needs to

             examine a larger portion of a frame’s headers for additional filtering purposes. Additional 40 bytes in

             order to perform more sophisticated functions relative to IPv4 Layers 3 and 4.

             If there is a high error rate (invalid frames) in the network, cut-through switching can have a

             negative impact on bandwidth.

            

             Fragment Free

             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.

            Frame will be checked into the data field to make sure no fragmentation has occurred.

            This mode provides better error checking than cut-through, with practically no increase in latency.

            High-performance computing (HPC) applications require process-to-process latencies of 10

            microseconds or less.

1.6 Switching domains

-       Collision Domains: Hub-based Ethernet segment, devices compete for the medium, because decives must take turns when transmitting. In switch every port have his own collision domains.

-       Broadcast Domains: Switches filter most frames based on MAC address, they do not filter broadcast frames. Interconnected switches are  single broadcast domains.

Only router can divide Layer 2 broadcast domains.

1.7 Alleviating Network Congestion.

Characteristics of switches that contribute to alleviating network congestion:

 High port density - Switches have high-port densities: 24- and 48-port switches are often just 1 rack unit (1.75 inches) in height and operate at speeds of 100 Mb/s, 1 Gb/s, and 10 Gb/s. Large enterprise switches may support many hundreds of ports.     

Large frame buffers - The ability to store more received frames before having to start dropping them is useful, particularly when there may be congested ports to servers or other parts of the network.     

Port speed - Depending on the cost of a switch, it may be possible to support a mixture of speeds. Ports of 100 Mb/s, and 1 or 10 Gb/s are common (100 Gb/s is also possible).     

Fast internal switching - Having fast internal forwarding capabilities allows high performance. The method that is used may be a fast internal bus or shared memory, which affects the overall performance of the switch.     

Low per-port cost - Switches provide high-port density at a lower cost. For this reason, LAN switches can accommodate network designs featuring fewer users per segment, therefore, increasing the average available bandwidth per user.

        

Layer 2 switches can send traffic based on the destination MAC address.

Process of the switch when receiving a frame with a address destination.

11)   Store the Mac address source

22)   If not in MAC-Address-Table Arp broadcast to all port except the ingress port.