CCNA focuses on networks for SMBs (small, medium businesses)˳
A hierarchical design model is recommended˳
Easier to manage and expand˳
Problems are solved more quickly˳
Hierarchical design divides the network into 3 layers˳
Core, (CL)˳
Distribrution, (DL)˳
Access, (AL)˳
Each layer provides specific functions˳
This “modularity” facilitates scalability and performance˳
Access Layer, (AL): lowest
Interfaces with the end device (user)˳
Includes routers, switches, bridges, hubs and wireless APs˳
Provides a means of connecting devices to the network and controlling which one communicate on the network˳
Distribution Layer, (DL):
Aggregates data received from the AL before transmitting to the CL for routing˳
Controls traffic flow using policies and delineates broadcast domains with VLANs defined at the AL˳
VLANs allow traffic segmentation (separate subnetworks)˳
DL switches are typically high-performance devices that have high availability and redundancy to ensure reliability˳
Core Layer, (CL):
The high-speed backbone or the internetwork˳
Critical for interconnectivity between distribution layer devices ? needs to be highly available and redundant˳
Often connects to Internet resources˳
Aggregates tfc fm all devices, so it must be capable of forwarding large amounts of data quickly˳
Note: smaller networks often combine the distribution and core layers˳
Three Logical Laye3rs are separated into a well-defined hierarchy˳
It is much harder to see these layers physically˳
Benefits of a Hierarchical Network:
Scalability:
Hierarchical networks scale very well˳
The modularity allows you to replicate design elements˳
Expansion is easy to plan and implement˳
Redundancy:
As a network grows, availability becomes more important˳
Availability increases dramatically with hierarchical networks˳
E˳G˳ AL switches connect to 2 DL switches˳ If one DL switch fails, the AL switch can switch to the other one˳
Redundancy is limited is at the access layer˳ Typically, end devices do not connect to multiple switches˳
Performance:
Properly designed networks can achieve near wire speed btwn all devices˳
Security:
AL switches can be configured to provide control over which devices are allowed to connect to the network˳
More advanced security policies available at the DL˳
Some AL switches support L3 functionality, but it is usually the job of the DL switches, because they can process it much more efficiently˳
Manageability:
Changes can be repeated across all devices in a layer because they presumably perform the same functions˳
Deployment of new switches is simplified because configs can be copied with few modifications˳
Consistency within each layer simplifies troubleshooting˳
Maintainability:
Because of their modularity and scalability, hierarchical networks are easy to maintain˳
This also means these networks are less expensive˳
With other designs, manageability becomes increasingly complicated as the network grows˳
Principles of Hierarchical Network Design:
Hierarchical design is no guarantee of good design˳
Simple guidelines help differentiate btwn well-designed and poorly designed hierarchical networks˳
Network Diameter:
Usually the first thing to consider˳
The # of devices a packet crosses to reach its destination˳
Small diameter ensures low and predictable latency˳
Bandwidth Aggregation, (adding together):
Combines links btwn switches to achieve up throughput˳
Cisco has a proprietary link aggregation technology called EtherChannel˳
Aggregated links are indicated by multiple dotted lines with an oval or a single, dotted line with an oval˳
Can be used at every layer (less common @ AL)˳
Redundancy:
Redundancy can be provided in a number of ways˳
E˳G˳ 2x connections btwn devices, or 2x devices˳
Redundant links can be expensive˳
Designing redundancy starts at the AL˳ You ensure that you accommodate all network devices ? 3 of AL switches˳
This helps determine 3 of DL switches ? CL switches˳
What is a Converged network?
SMBs are increasingly running voice, video and data˳
Convergence is the process of combining these˳
Until recently this was limited to large enterprises˳
Legacy (older) equipment hinders convergence˳
Because analog phones have not yet been replaced, you will also see legacy PBX telephone and IP-based systems˳
Convergence is now easier and less expensive˳
With a convergence there is just one network to manage˳
This costs less to implement and manage˳
IT cabling requirements are simplified˳
Convergence also creates new opportunities˳
You can tie voice and video directly into an employee’s PC˳
No need for an expensive phone or video equipment˳
Softphones (Cisco IP |Communicator) offer a lot of flexibility˳
With software businesses can quickly convert to converged networks with little capital expense˳
With cheap webcams videoconferencing can be added˳
Separate Voice, Video and Data Networks:
Voice networks contain isolated phone lines running to a PBX (Private BDXT Exchange) switch located in a Telco wiring closet PSTN (Public Switch Telephone Network)˳
Telco closet often separate fm the data and video closets˳
New phone ? a new line to the PBX˳
Using a properly designed hierarchical network voice lines can be added with little or no impact˳
Now that networks can accommodate the BW it makes sense to converge˳
Considerations for Hierarchical Network Switches:
Tfc Flow Analysis:
The process of measuring BW usage and analyzing it for performance tuning, planning, and HW improvement˳
To select the appropriate gear in a hierarchical network, you need to spec out tfc flows, users and servers˳
Networks must be designed with an eye on growth˳
Done using tfc flow analysis software˳
Should consider port densities and forwarding rates to ensure adequate growth capability˳
Analysis Tools:
Many tfc flow analysis tools are available˳
E˳G˳ Solarwinds Orion 8˳1 NetFlow Analysis˳
User Communities Analysis:
Identifies user grpings and their impact on net performance˳
Affects port density and tfc flow, which influences the selection of network switches˳
Typically users are grped according to job function˳
E˳G˳ HR one floor and Finance on another˳
Each dept˳ has different users and needs, and requires access to different resources through the network˳
Choose switches that have enough ports to meet the dept needs and pwrful enough to accommodate tfc˳
Good network design also factors in the growth˳
Investigate the tfc generated by end-user applications˳
Some user communities generate a lot, some do not˳
The location of the user communities influences where data stores and server farms are located˳
By locating users close to their servers, you can reduce network diameter, reducing the impact on other users˳
However, usage is not always bound by department or physical location˳
Data Stores and Data Servers Analysis:
Data stores can be servers, SANs, NAS, tape bu units, or any other storage device or component˳
Considers both client-server and server-server tfc˳
Client-server tfc typically traverses multiple switches˳
BW aggregation and switch forwarding rates can help eliminate bottlenecks for this type of tfc˳
Some server apps generate high volumes btwn servers˳
These server shouls be located close to each other (i˳e˳ secured data centers)˳
Tfc across data center switches is typically very high˳
Requires higher performing switches˳
Topology Diagrams:
A graphical representation of a network infrastructure˳
Shows how all switches are interconnected, including which ports interconnect devices˳
It shows where and how many switches are in use˳
Can also contain info on device densities and user grps˳
Helps visually identify potential bottlenecks˳
Very difficult to create after the fact˳
Switch Features:
Switch Form Factors:
Fixed or modular config, and stackable or non-stackable˳
Thickness is expressed in rack units˳ (i˳e˳ 1U, 3U)˳
Fixed Config Switches – Cannot add hardware˳
Modular Switches – chassis allows for multiple line cards which contain the ports˳
The larger the chassis, the more modules it can support˳
Stackable Switches:
Can be interconnected using a special backplane cable that provides high-bandwidth throughput btwn the switches˳
Cisco’s StackWise technology allows you to interconnect up to nine switches using fully redundant backplane connections˳
Stacked switches effectively operate as a single larger switch˳
Desirable where fault tolerance and BW availability are critical and a modular switch is too costly˳
Performance:
Port Density:
Port density is the 3 of ports available per switch˳
Fixed sitches typically 1,000 ports!
Large enterprise networks require high density, modular switches to make the best use of space and pwr˳
Also prevent uplink bottlenecks˳
A series of fixed swtches consume many additional ports for BW aggregation btwn switches˳
Whith a modular switch, aggregation is less of an issue because the chassis backplane provides the BW˳
Forwarding Rates:
The processing capabilities of a switch in bps˳
Switch product lines are classified by forwarding rates˳
If this rate is too low, it cannot accommodate wire-speed across all ports˳
Wire speed = rate that each port is capable of (10Mbps etc)˳
E˳G˳ 48-port GbE switch at wire speed = 48Gbps of tfc˳
If the switch only supports 32 Gbps (internally), it cannot run at full wire speed across all posrts simultaneously˳
Access switches typically do not need full wire speed because they are physically limited by their uplinks to the DL˳
Link Aggregation:
Determine if there are enough ports to aggregate to support the required BW˳
E˳G˳ GbE 24-port switch could generate up to 24 Gbps˳
If it is connected to the network by a single cable, it can only forward 1 Gbps to the rest of the network˳
That results in 1/24th wire speed for each of the 24 devices˳
Link aggregation helps to reduce these bottlenecks by allowing up to 8 ports to be grped, providing up to 8 Gbps˳
With multiple 10GbE uplinks very high throughput rates can be achieved˳
Cisco uses the term EtherChannel = aggregated ports˳
Power over Ethernet (PoE):
PoE allows a switch to deliver power over existing Ethernet˳
Can be used by IP phones and some wireless APs˳
Allows more flexibility for equipment installations˳
Adds considerable cost to the switch˳
PoE switch marked with a `V`for volts˳
Layer 3 Functions:
Typically, switches operate at L2 and deal primarily with MAC addresses˳
L3 switches offer advanced functionality˳
L3 switches = multilayer switches˳
Switch features in a Hierarchical Network:
Access Layer switch Features:
Port security – first line of defense for a network˳
How many or what devices are allowed to connect˳
All Cisco switches support port layer security˳
VLANs – component of converged networks˳
Voice tfc is typically given a separate VLAN˳
Port speed:
Fast Ethernet is adequate for VoIP and most data tfc˳
PoE – much more expensive, so use only when required˳
Link Aggregation – supported at all 3 lvls˳
QoS – needed for VoIP˳
Distribution Layer Switch features:
Collect all AL switch data and forward it to the CL switches˳
Provides the inter-VLAN routing functions˳
DL switches have higher processing capabilities than AL˳
Need L3 to support inter-VLAN routing˳
Security Policies:
Need L3 so advanced security policies can be applied˳
ACLs control tfc flows through a network˳
ACLs allow switches to filter tfc˳
ACLs are CPU-intensive because they need to inspect every packet and match ACL rules˳
Placing ACLs at the DL also reduces the 3 of switches that require the extra mgmt configuration˳
Policy-based connectivity and departmentaléworkgroup access to the core layer˳
Quality of Service:
DL switches need to maintain the priorities of tfc coming fm the AL switches that have implemented QoS˳
If not all the devices support QoS, the benefits will be reduced -˳ poor performance and quality˳
DL switches are under high demand˳
They need redundancy for adequate availability˳
DL switches are typically implemented in pairs˳
Recommended that they support multiple, hot swappable pwr supplies˳
Finally, they need to support link aggregation and high-bandwidth aggregated links back to the core˳
Core Layer Switch Features:
The CL is the high-speed backbone˳
The forwarding rate is dependent on the number of devices participating in the network˳
If you choose an inadequate switch at the core, you face potential bottleneck issues slowing down all tfc˳
CL switches should support aggregated 10GbE˳
L3 redundancy has faster convergence than L2, so, ensure CL switches support L3 functions˳
CL switches should support FULL redundancy features˳
QoS is important at the core since high-speed WAN access is often prohibitivel expensive˳
Switches for SMBs:
Identify the Cisco switches used in SMB applications˳
The features of Cisco Catalyst Switches:
You cannot simply select a switch by the size of a business˳
Businesses are often cross integrated with other entities˳
A 6500 makes sense as an AL switch where there are hundreds of users in an area, such as a stock exchange˳
Cat Express 500 – forwarding rates = 8˳8 – 24 Gbps˳
Cat 2960 – L3, QoS, no PoE, 16 – 32 Gbps˳
Cat 3560 – enterprise-class PoE, QoS, 32 – 128 Gbps˳
Cat 3750 – stackable high performance˳
Cat 4500 – DL midrange modular – up to 136 Gbps˳
Cat 4900 – data center˳
Cat 6500 – DL and CL – up to 720 Gbps˳
Miscellaneous:
MDF – Main Distribution Facility˳
Gi 0é1 – abbreviation for Gigabit Ethernet ports˳
Spanning Tree – protocols allows redundant paths, but shuts down some links to avoid switching loops˳
Source by https://ezinearticles˳com/?LAN-Design-and-the-Hierarchical-Network-Model&id=1414904
