Download LAN design

Network design
Topic 4
LAN design
Agenda
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Modular design
Hierarchal model
Campus network design
Design considerations
Switch features
Problem of flat networks
• Large broadcast domains
– Broadcast packets interrupt the CPU on each host
• Routers, workstations and servers
• Large routing domains
– CPU processing hit on routers which are required
to process updates and advertisements from
many other routers
• Flat networks are adequate only for very small
networks
Hierarchical design model
Each element has
a specific set of
functions and
services and a
specific role
Core layer
• Performance
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High-speed backbone of the internetwork
Sufficient capacity
Low latency with a limited and consistent network diameter
No filtering and traffic inspection to slow down flows
• Interconnectivity
– Connects campus networks to edge distribution (Internet services)
– Highly available and highly reliable with redundant and hot
swappable components
– Adapts to change quickly with fast converging protocols
• Scalable
– Distribution layer switches (routers) can be added without
increasing the diameter
– Collapsed core, where core and distribution functions combined
onto same device for smaller networks
Distribution layer
• Aggregates the data received from the access layer
switches before it is transmitted to the core layer
– Controls the flow of network traffic using policies
• Filtering (ACLs) to control traffic moving onto the backbone
and between VLANs
– Defines the size of broadcast domains
– Routes traffic between VLANs
– Controls and optimises network traffic to the core
• Redistributes less optimal protocols to maintain optimal
protocols across the core
• Uses summarised routes to core to simplify routing tables
• High availability and redundancy to ensure reliability
– Two or more high performance switches, duplicate links and dual
power supplies
Access layer
• Switches and wireless access points to connect
users
• VLAN access for applications with specific
requirements such as voice
• Controls which devices are allowed to
communicate on the network
– Access layer should be controlled so that users can
not add a fourth layer by connecting extra
switches, hubs, routers ‘adding a chain’…
– Switchport security
– BPDUguard
Benefits of a hierarchical network
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Scalability
Availability and redundancy
Performance
Security
Manageability
Maintainability
Cost efficiency
Campus network design
Campus network design
• Campus backbone
– high-performance, switched backbone that connects buildings and different
parts of the campus
• Building distribution
– Distribution layer switches which aggregates the switches in the wiring closets
of the building
• Building access
– Workstations, IP phones and endpoints connected to access switches and
wireless access point
• Server farm
– Accessed over the core and provides internal server resources to users such as
application, file, print, e-mail, and Domain Name System (DNS) services.
• Network management
– Access to management devices that support monitoring, logging,
troubleshooting and security functions
• Edge distribution
– at provides connectivity between the campus and the rest of the internetwork,
WAN services
Modular design
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Minimise costs by using only required features
Capacity planning – less bandwidth waste
Network management systems can be distributed
Simple and easy to understand
Testing simplified
Fault isolation is improved
Scalable and consistent
Facilitates change
Design guidelines
• Use hierarchical and modular models
• Examine single points of failure and build in
redundancy
• Characterise application and protocol traffic
• Analyse bandwidth availability and determine
capacity required
– Design the access layer first
– Design the distribution layer next
– Design the core layer
Redundancy
• Duplicate network components to eliminate single points of failure
– Core and distribution router or switch, trunk links, power supplies
– Redundant data centres!
• Expensive to deploy and maintain
– Select a level of redundancy that matches the customer‘s requirements for
availability and affordability
– Identify critical applications, systems, internetworking devices, and links
– Analyse the customer's tolerance for risk and the consequences of not
implementing redundancy
– Discuss with the customer the tradeoffs of redundancy versus low cost, and
simplicity versus complexity
• Redundancy facilitates load balancing
– Requires routing protocol support
• EIGRP and variance command for unequal load balancing
• OSPF equal cost load balancing
Network diameter
• Network diameter is the number of devices that a
packet has to cross before it reaches its
destination.
– The number of switches in the path between
endpoints
• Keep the network diameter low to avoid high
impact from device latency
– Device latency is the delay the packet incurs crossing
the switch.
• STP/RSTP is optimised for a network diameter of
seven
– Diameters greater that seven will produce errors
Designing links
• Identify user communities
– Consider port density – number of switchports needed by the user community
– Consider future growth
– Consider the traffic flows generated from the network applications and the
locations of servers used
• Data Stores and Data Servers Analysis
– Consider the location of data stores: such as servers, storage area networks
(SANs), network-attached storage (NAS)
– Consider client-server traffic and use bandwidth aggregation and switch
forwarding rates to eliminate bottlenecks for traffic crossing many switches
– Consider Server-server traffic and locate servers together to reduce high traffic
impact from rest of network
• Traffic flow analysis
– Use traffic flow analysis to ensure capacity is sufficient
• Capacity on trunks
• Internal forwarding rates on switches
Design capacity
• Bandwidth aggregation
– Consider the bandwidth requirements of each
layer and aggregate links for more bandwidth
– Link aggregation allows multiple switch port links
to be combined to achieve higher throughput
between switches.
– EtherChannel, Cisco® proprietary link aggregation
technology
Create topology diagrams
• A topology is a map of an internetwork
– Indicates network segments, interconnection points
and user communities, servers and data stores
– Indicates size and scope of networks
– Types of internetworking devices
• Access, distribution and core switches, APs, Routers
– Redundant paths and aggregated links
• Document network infrastructure in a topology
diagram
Switch performance features
• Port density
– Number of ports available on a single switch
– Higher port densities use less space and power and require less uplink ports
and less port aggregation for uplinks
• Forwarding rates
– How much data the switch can process per second – the processing ability
– Wire speed is the data rate that each port on the switch is capable of attaining
Fa or Gig
– Does the forwarding rate allow full wire speed across all ports? Is this required?
Yes for distribution switches, probably not for access layer switches
• Link aggregation
– To reduce bottlenecks of traffic by allowing up to eight switch ports to be
bound together for data communications
– 8 * 1Gb/s = 8 Gbps throughput on uplink
– EtherChannel technology allows the grouping of switchports to create one
logical Ethernet link
– Fault tolerance and high-speed links between switches, routers, and servers
Switch features
• Switch form factors
– Fixed configuration switches:
• Cannot be expanded with extra features such as ports
– Modular configuration switches
• Buy a chassis of a particular size and modular line cards with
the switchports – more flexible
– Stackable switches
• StackWise® technology to connect up to nine switches using a
special backplane cable
• Higher bandwidth throughput between the switches than
using line ports
• Rack size
– thickness of the switch expressed in number of rack units
– 1 rack unit (1U)
Other switch features
• Power over Ethernet
– Switch delivers power using existing Ethernet cabling
– Wireless Access Points and phones can be located
where cables are
– Adds considerable cost to switch
– Balance cost of switch to cost of power packs and
installing outlets
• Multilayer switches
• Perform layer 3 and 4 functions such as routing
and enforcing security policy with ACLs
Access layer switch features
• Port security
– By number of hosts and by MAC address
• VLANs
– For security domains and performance (voice VLAN)
• Port speed and link aggregation
– Fast Ethernet or Gigabit Ethernet
– Reserve extra switchports for aggregation, faster uplink connections
• Power over Ethernet (PoE)
– Extra expensive – is it required for IP phones and Access Points?
• Internal forwarding rate
– Does not need to be as high as combined switchport speed as end devices
unlikely to be fully used all the time
• QoS support
– Classification of voice and video traffic in a converged network
Distribution layer switch features
• Layer 3 support
– Inter-VLAN routing
– Security policies – ACLS control where traffic can flow
– QoS – classified traffic moves through priority queues more quickly
• Redundancy
– Two power supplies which are hot swappable
• High forwarding rates
– Layer 3 functions are processor intensive
• Link aggregation
– Accept aggregated links from access layer switches
– Ether-channel capabilities
• Performance
– Move traffic to core with high speed aggregated links – Gig and 10 Gig
Core layer switch features
• Very high forwarding rates
– Depends on number and location of devices and their traffic flows
– Use traffic flow analysis to determine the rate required
• Link aggregation
– to ensure adequate bandwidth support for aggregated 10 GbE
connections
• Redundancy
– Fast convergence- the time to resume after hardware or link failure
– Layer 3 protocols are faster to recover than layer 2 protocols
– Hot-swappable hardware such as power supplies and fans to avoid
downtime
• Quality of Service (QoS)
– Moving traffic through the network at the optimal rates for the type of
traffic
Selecting switches
• What are the business goals for performance level
or redundancy?
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How many end devices?
How many access layer switches?
Estimate traffic that each end device generates
Select distribution switches able to process traffic
• Performance and forwarding rates , interfaces
• What technology features are required?
• Build in redundancy for distribution layer
– Select core switches able to process traffic crossing
backbone
• Performance and forwarding rates, interfaces
• Build in redundancy for core layer
Agenda
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Modular design
Hierarchal model
Campus network design
Design considerations
Switch features