Chapter 1. LAN Design
Introduction
The campus local area network (LAN) is the network that supports devices people use within a location to connect to information.
Campus Wired LAN Designs
Cisco Validated Designs
Hierarchical Design Model
Hierarchical design model break the design up into modular groups or layers.
Breaking the design up into layers allows each layer to implement specific functions
which simplifies
• the network design and therefore
• the deployment and management of the network.
The access layer provides endpoints and users direct access to the network
The distribution layer aggregates access layers and provides connectivity to services.
The core layer provides connectivity between distribution layers for large LAN environments.
some smaller enterprise networks may implement a two-tier hierarchical design
Modular structuring of the network into small, easy-to-understand elements also facilitates resiliency via improved fault isolation.
Resilience, refers to a system's ability to adapt to failures and to resume (recover) normal operations when the failure has been resolved.
Expanding the Network
Design for Scalability
The network designer must develop a strategy to enable the network to be available and to scale effectively and easily.
Included in a basic network design strategy are the following recommendations:
Use expandable, modular equipment or clustered devices that can be easily upgraded to increase capabilities. Device modules can be added to the existing equipment to support new features and devices without requiring major equipment upgrades. Some devices can be integrated in a cluster to act as one device to simplify management and configuration.
Design a hierarchical network to include modules that can be added, upgraded, and modified, as necessary, without affecting the design of the other functional areas of the network. For example, creating a separate access layer that can be expanded without affecting the distribution and core layers of the campus network.
Create an IPv4 or IPv6 address strategy that is hierarchical. Careful address planning eliminates the need to re-address the network to support additional users and services.
Choose routers or multilayer switches to limit broadcasts and filter other undesirable traffic from the network. Use Layer 3 devices to filter and reduce traffic to the network core.
More advanced network design requirements include
Implementing redundant links in the network between critical devices and between access layer and core layer devices.
Implementing multiple links between equipment, with either link aggregation (EtherChannel) or equal cost load balancing, to increase bandwidth. Combining multiple Ethernet links into a single, load-balanced EtherChannel configuration increases available bandwidth. EtherChannel implementations can be used when budget restrictions prohibit purchasing high-speed interfaces and fiber runs.
Using a scalable routing protocol and implementing features within that routing protocol to isolate routing updates and minimize the size of the routing table.
Implementing wireless connectivity to allow for mobility and expansion.
Planning for Redundancy
Redundancy is an important part of network design for preventing disruption of network services by minimizing the possibility of a single point of failure.
One method of implementing redundancy is by installing duplicate equipment and providing failover services for critical devices.
Failover: a method of protecting computer systems from failure, in which standby equipment automatically takes over when the main system fails.
Another method of implementing redundancy is redundant paths to offer alternate physical paths for data to traverse the network. Due to the operation of switches, redundant paths in a switched Ethernet network may cause logical Layer 2 loops. For this reason, Spanning Tree Protocol (STP) is required.
STP eliminates Layer 2 loops when redundant links are used between switches. It does this by providing a mechanism for disabling redundant paths in a switched network until the path is necessary, such as when failures occur. STP is an open standard protocol, used in a switched environment to create a loop-free logical topology.
Failure Domains
A failure domain is the area of a network that is impacted when a critical device or network service experiences problems.
Smaller failure domains reduce the impact of a failure on company productivity. They also simplify the troubleshooting process, thereby, shortening the downtime for all users.
Limiting the Size of Failure Domains
it is easiest and usually least expensive to control the size of a failure domain in the distribution layer
Network errors can be contained to a smaller area; thus, affecting fewer users
Switch Block Deployment
Routers, or multilayer switches, are usually deployed in pairs, with access layer switches evenly divided between them. This configuration is referred to as a building, or departmental, switch block
Each switch block acts independently of the others. As a result, the failure of a single device does not cause the network to go down. Even the failure of an entire switch block does not affect a significant number of end users.
Increasing Bandwidth
Implementing EtherChannel
As traffic from multiple links converges onto a single, outgoing link, it is possible for that link to become a bottleneck.
Link aggregation allows an administrator to increase the amount of bandwidth between devices by creating one logical link made up of several physical links
EtherChannel is a form of link aggregation used in switched networks
The EtherChannel is seen as one logical link using an EtherChannel interface.
Most configuration tasks are done on the EtherChannel interface, instead of on each individual port, ensuring configuration consistency throughout the links
Expanding the Access Layer
Implementing Wireless Connectivity
Providing wireless connectivity offers many advantages, such as increased flexibility, reduced costs, and the ability to grow and adapt to changing network and business requirements.
There are many considerations when implementing a wireless network, such as the
• types of wireless devices to use,
• wireless coverage requirements,
• interference considerations,
• and security considerations.
Fine-tuning Routing Protocols
Managing the Routed Network
Link-state routing protocols such as Open Shortest Path First (OSPF), works well for larger hierarchical networks where fast convergence is important.
OSPF routers establish and maintain neighbor adjacency or adjacencies, with other connected OSPF routers.
Routers reach a FULL state of adjacency when they have synchronized views on their link-state database.
link state updates are sent when network changes occur
Additionally, OSPF supports a two-layer hierarchical design, referred to as multiarea OSPF
All multiarea OSPF networks must have an Area 0, also called the backbone area. Non-backbone areas must be directly connected to area 0.
Another popular routing protocol for larger networks is Enhanced Interior Gateway Routing Protocol (EIGRP).
Cisco developed EIGRP as a proprietary distance vector routing protocol with enhanced capabilities.
EIGRP uses multiple tables to manage the routing process
Selecting Network Devices
Switch Hardware
Switch Platforms
There are five categories of switches for enterprise networks
Campus LAN Switches - To scale network performance in an enterprise LAN, there are core, distribution, access, and compact switches. These switch platforms vary from fanless switches with eight fixed ports to 13-blade switches supporting hundreds of ports. Campus LAN switch platforms include the Cisco 2960, 3560, 3650, 3850, 4500, 6500, and 6800 Series.
Cloud-Managed Switches - The Cisco Meraki cloud-managed access switches enable virtual stacking of switches. They monitor and configure thousands of switch ports over the web, without the intervention of onsite IT staff.
Data Center Switches - A data center should be built based on switches that promote infrastructure scalability, operational continuity, and transport flexibility. The data center switch platforms include the Cisco Nexus Series switches and the Cisco Catalyst 6500 Series switches.
Service Provider Switches - Service provider switches fall under two categories: aggregation switches and Ethernet access switches. Aggregation switches are carrier-grade Ethernet switches that aggregate traffic at the edge of a network. Service provider Ethernet access switches feature application intelligence, unified services, virtualization, integrated security, and simplified management.
Virtual Networking - Networks are becoming increasingly virtualized. Cisco Nexus virtual networking switch platforms provide secure multi-tenant services by adding virtualization intelligence technology to the data center network.
When selecting switches, network administrators must determine the switch form factors. This includes fixed configuration, modular configuration, stackable, or non-stackable.
The thickness of the switch, which is expressed in the number of rack units, is also important for switches that are mounted in a rack