In fact, what separates you from tearing down the entire infrastructure is often a single command. While this is important, today we will focus on network design. Since networks grow organically, you need to plan everything from the beginning. To avoid the worst, you should know the lifecycle of a network.

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Moreover, Layer 2 switches deliver the ability to increase bandwidth to the wiring closet without adding unnecessary complexity to the network. At Layer 2, no modification is required to the frame content when going between Layer 1 interfaces, such as Fast Ethernet to 10 Gigabit Ethernet. In review, the network design properties of current-generation Layer 2 switches include the following: Designed for near wire-speed performance Built using high-speed, specialized ASICs Switches at low latency Scalable to a several switch topology without a router or Layer 3 switch Supports Layer 3 functionality such as Internet Group Management Protocol IGMP snooping and QoS marking Offers limited scalability in large networks without Layer 3 boundaries Layer 3 Switching In-Depth Layer 3 switching is hardware-based routing.

Layer 3 switches overcome the inadequacies of Layer 2 scalability by providing routing domains. A Layer 3 switch performs everything on a packet that a traditional router does, including the following: Determines the forwarding path based on Layer 3 information Validates the integrity of the Layer 3 packet header via the Layer 3 checksum Verifies and decrements packet Time-To-Live TTL expiration Rewrites the source and destination MAC address during IP rewrites Updates Layer 2 CRC during Layer 3 rewrite Processes and responds to any option information in the packet such as the Internet Control Message Protocol ICMP record Updates forwarding statistics for network management applications Applies security controls and classification of service if required Layer 3 routing requires the ability of packet rewriting.

Packet rewriting occurs on any routed boundary. Figure illustrates the basic packet rewriting requirements of Layer 3 routing in an example in which two workstations are communicating using ICMP.

Without knowing the MAC address of the default gateway, Workstation A cannot send any traffic outside the local subnet.

Figure illustrates the Layer 2 and Layer 3 rewriting at different places along the path between Workstation A and B. This figure and example illustrate the fundamental operation of Layer 3 routing and switching.

The primary difference between the packet-forwarding operation of a router and Layer 3 switching is the physical implementation. Layer 3 switches use different hardware components and have greater port density than traditional routers. These concepts of Layer 2 switching, Layer 3 forwarding, and Layer 3 switching are applied in a single platform: the multilayer switch. Because it is designed to handle high-performance LAN traffic, a Layer 3 switch is locatable when there is a need for a router and a switch within the network, cost effectively replacing the traditional router and router-on-a-stick designs of the past.

Understanding Multilayer Switching Multilayer switching combines Layer 2 switching and Layer 3 routing functionality.

Generally, the networking field uses the terms Layer 3 switch and multilayer switch interchangeably to describe a switch that is capable of Layer 2 and Layer 3 switching. In specific terms, multilayer switches move campus traffic at wire speed while satisfying Layer 3 connectivity requirements. This combination not only solves throughput problems but also helps to remove the conditions under which Layer 3 bottlenecks form.

Moreover, multilayer switches support many other Layer 2 and Layer 3 features besides routing and switching. For example, many multilayer switches support QoS marking. Combining both Layer 2 and Layer 3 functionality and features allows for ease of deployment and simplified network topologies. Moreover, Layer 3 switches limit the scale of spanning tree by segmenting Layer 2, which eases network complexity.

In addition, Layer 3 routing protocols enable load-balancing, fast convergence, scalability, and control compared to traditional Layer 2 features. In review, multilayer switching is a marketing term used to refer to any Cisco switch capable of Layer 2 switching and Layer 3 routing. From a design perspective, all enterprise campus designs include multilayer switches in some aspect, most likely in the core or distribution layers.

Moreover, some campus designs are evolving to include an option for designing Layer 3 switching all the way to the access layer with a future option of supporting Layer 3 network ports on each individual access port. Over the next few years, the trend in the campus is to move to a pure Layer 3 environment consisting of inexpensive Layer 3 switches. For brevity, this section highlights a few popular models used in the campus, core backbone, and data center. For a complete list of Cisco switches, consult product documentation at Cisco.

They are found in a wide variety of installs not only including campus, data center, and backbone, but also found in deployment of services, WAN, branch, and so on in both enterprise and service provider networks.

For the purpose of CCNP SWITCH and the scope of this book, the Cisco Catalyst family of switches are summarized as follows: Scalable modular switch up to 13 slots Supports up to 16 Gigabit Ethernet interfaces per slot in an over-subscription model Up to 80 Gbps of bandwidth per slot in current generation hardware Supports Cisco IOS with a plethora of Layer 2 and Layer 3 switching features Optionally supports up to Layer 7 features with specialized modules Integrated redundant and high-available power supplies, fans, and supervisor engineers Supports Layer 3 Non-Stop Forwarding NSF whereby routing peers are maintained during a supervisor switchover.

Backward capability and investment protection have lead to a long life cycle Cisco Catalyst Family of Switches The Cisco Catalyst family of switches is a vastly popular modular switch found in many campus networks at the distribution layer or in collapsed core networks of small to medium-sized networks.

Collapsed core designs combine the core and distribution layers into a single area. The Catalyst is one step down from the Catalyst but does support a wide array of Layer 2 and Layer 3 features. In summary, the Cisco Catalyst family of switches are summarized as follows: Scalable module switch with up to 10 slots Supports multiple 10 Gigabit Ethernet interfaces per slot Supports Cisco IOS Supports both Layer 2 switching and Layer 3 switching Optionally supports integrated redundant and high-available power supplies and supervisor engines Cisco Catalyst G, , and Family of Switches The Cisco Catalyst G, , and family of switches are popular switches used in campus networks for fixed-port scenarios, most often the access layer.

These switches are summarized as follows: Available in a variety of fixed port configurations with up to 48 1-Gbps access layer ports and 4 Gigabit Ethernet interfaces for uplinks to distribution layer Supports Cisco IOS Supports both Layer 2 and Layer 3 switching Not architected with redundant hardware Cisco Catalyst Family of Switches The Cisco Catalyst family of switches are Layer 2-only switches capable of few Layer 3 features aside from Layer 3 routing.

These features are often found in the access layer in campus networks. These switches are summarized as follows: Available in a variety of fixed port configurations with up to 48 1-Gbps access layer ports and multiple Gigabit Ethernet uplinks Supports Cisco IOS Supports only Layer 2 switching Not architected with redundant hardware Nexus Family of Switches The Nexus family of switches are the Cisco premier data center switches.

The product launch in ; and thus, the Nexus software does not support all the features of Cisco IOS yet. Nonetheless, the Nexus is summarized as follows: Modular switch with up to 18 slots Supports up to Gbps per slot Supports Nexus OS NX-OS slot chassis is built on front-to-back airflow Supports redundant supervisor engines, fans, and power supplies Nexus and Family of Switches The Nexus and family of switches are low-latency switches designed for deployment in the access layer of the data center.

These switches are Layer 2-only switches today but support cut-through switching for low latency. Hardware and Software-Switching Terminology This book refers to the terms hardware-switching and software-switching regularly throughout the text.

The industry term hardware-switching refers to the act of processing packets at any Layers 2 through 7, via specialized hardware components referred to as application-specific integrated circuits ASIC. These terms are used interchangeably throughout the text.

Multilayer switching MLS is another term commonly used to describe hardware-switching. The term MLS can be confusing; for example, with the Catalyst , the term MLS described a legacy hardware-switching method and feature. Switching and routing traffic via hardware-switching is considerably faster than the traditional software-switching of frames via a CPU.

Many ASICs, especially ASICs for Layer 3 routing, use specialized memory referred to as ternary content addressable memory TCAM along with packet-matching algorithms to achieve high performance, whereas CPUs simply use higher processing rates to achieve greater degrees of performance.

ASICs integrate not only on Supervisor Engines, but also on individual line modules of Catalyst switches to hardware-switch packets in a distributed manner. ASICs do have memory limitations. For example, the Catalyst family of switches can accommodate ACLs with a larger number of entries compared to the Catalyst E family of switches due to the larger ASIC memory on the Catalyst family of switches.

Generally, the size of the ASIC memory is relative to the cost and application of the switch. As products continue to evolve and memory becomes cheaper, ASICs gain additional memory and feature support. Use the content in this section as information for sections that refer to the terminology. The next section changes scope from switching hardware and technology to campus network types. Campus Network Traffic Types Campus designs are significantly tied to network size.

However, traffic patterns and traffic types through each layer hold significant importance on how to shape a campus design. Each type of traffic represents specific needs in terms of bandwidth and flow patterns.

Table lists several different types of traffic that might exist on a campus network. As such, indentifying traffic flows, types, and patterns is a prerequisite to designing a campus network. Table Common Traffic Types Traffic Type.


Cisco PPDIOO | A Network Life Cycle

This methodology is composed by six phases closely related: prepare, plan, design, implement, operate, optimize. Lowering the total cost of network ownership: Companies try to lower the total cost of network ownership while they add new technologies to an existing network, procure equipment, train staff, manage network performance, and maintain the network. For example, an IP Communications system could be outfitted with a customer relationship application that enables incoming calls to automatically trigger the display of customer account information and contact history, providing staff with the information they need to respond quickly and effectively. Increasing availability: Downtime can adversely affect revenue and can reduce profitability through costs associated with the network staff having to troubleshoot and function in a reactive mode. High availability depends on carefully planned redundancy, sound security, and scalability and also requires diligence throughout the network lifecycle. Availability targets are influenced by business goals.


The PPDIOO network lifecycle

You can also properly make a plan for changes in infrastructure and changes in requirements for resources. PPDIOO also improve the networks availability because we are using a sound and solid network design and all alone the way we are validating our network operations. It also speed-up access to network resources and applications. One important thing to note that your network life cycle may not necessary to go through all the phases in the define order. It is quite likely to go into preparation phase, planning phase, design phase and implementation phase and then you may have to go back to planning phase to make some changes and then have to go at design phase forimplementing changes into design.

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