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Switches
Antonio González Torres
Hierarchical Network Design
The design of larger LANs includes identifying the following: An access layer that connects end users into the LAN A distribution layer that provides policy-based
connectivity between end-user LANs A core layer that provides the fastest connection
between the distribution points
LAN design goals
Functionality Scalability Adaptability Manageability
Functionality
The network must work. The network must allow users to meet their job requirements. The network must provide user-to-user and user-to-application connectivity with reasonable speed and reliability.
Scalability
The network must be able to grow. The initial design should grow without any major changes to the overall design.
Adaptability
The network must be designed with a vision toward future technologies. The network should include no element that would limit implementation of new technologies as they become available.
Manageability
The network should be designed to facilitate network monitoring and management to ensure ongoing stability of operation.
LAN design considerations
LAN design considerations The function and
placement of servers
Collision detection issues
Segmentation issues
Broadcast domain issues
Enterprise servers support all the users should be placed in the
main distribution facility (MDF).
Workgroup servers support a specific set of
users should be placed in the
intermediate distribution facility (IDF).
Server Placement
Segmentation
the process of splitting a single collision domain into smaller collision domains reduces the number of collisions allows for greater utilization of bandwidth Using Layer 2 devices such as bridges and
switches Routers reduce the size of the collision
domain and the size of the broadcast domain at Layer 3
LAN design methodology
Gather requirements and expectations
Analyze requirements and data
Design the Layer 1, 2, and 3 LAN structure, or topology
Document the logical and physical network implementation
Availability measures
Availability measures the usefulness of the network.
things that affect availability: Throughput Response time Access to resources
Every customer has a different definition of availability.
Design LAN Structure
The most common LAN topologies are star and extended star
The topology structure can be broken into OSI layers to determine devices to use
LAN design documentation
OSI layer topology map
LAN logical map LAN physical map Cut sheets VLAN logical map Layer 3 logical map Addressing maps
Document Logical Diagram
the flow of data in a network
A snapshot view of all LAN implementation
OSI layer topology map
This diagram shows how the devices and telecommunication closets are connected
Cut sheets
Cut sheets store detail information about the different connections in the network
VLAN logical map
VLAN logical maps show the inter VLAN and Intra VLAN interconnection using a router or trunking ports
Layer 3 logical map
These diagrams show the logical addresses different devices use to send and receive information
Addressing maps
Addressing maps show the logical addresses configured for each network device
Layers design
Layer 1 Design
•One of the most important components to consider when designing a network is the physical cabling.
Layer 1 Design Issue: Type of Cabling
copper or fiber-optic?
the overall structure of the cabling
Some rules on Cabling
Fiber-optic cable should be used in the backbone and risers in all cable designs.
Category 5e UTP cable should be used in the horizontal runs.
The cable upgrade should take priority over any other necessary changes.
Enterprises should also make certain that these systems conform to well-defined industry standards, such as the TIA/EIA-568-A specifications.
Star Topology Using Cat. 5 UTP
Typical MDF in Star Topology
In a simple star topology with only one wiring closet, the MDF includes one or more horizontal cross-connect (HCC) patch panels.
HCC patch cables are used to connect the Layer 1 horizontal cabling with the Layer 2 LAN switch ports.
The uplink port of the LAN switch, depending on the model, is connected to the Ethernet port of the Layer 3 router using a patch cable. At this point, the end host has a complete physical connection to the router port.
Multi-Building Campus
When hosts in larger networks exceed the 100-meter limitation for Cat. 5e UTP, more than one wiring closet is required.
Multiple wiring closets mean multiple catchment areas.
The secondary wiring closets are referred to as IDFs.
Extended-Star Topology in a Multi-Building Campus
Fiber-optic cable is normally used because the vertical cable lengths are typically longer than 100 meters
VCC is used to interconnect the various IDFs to the central MDF.
IDFs should be connected to the MDF by vertical cabling, also called backbone cabling.
Logical Diagram
the network topology model without all the details of the exact installation paths of the cables
the basic road map of the LAN
the locations and identification of the MDF and IDF wiring closets
the type and quantity of cables used to interconnect the IDFs with the MDF
the number of spare cables
detailed documentation of all cable runs, the identification numbers, and the port the run is terminated on at the HCC or VCC.
Layer 2 Design
Devices at Layer 2 determine the size of the collision domains.
Asymmetric Switching
provides more bandwidth to vertical cabling, uplinks, and servers
The desired capacity of a vertical cable run is greater than that of a horizontal cable run.
Determine the number of 10 Mbps and 100 Mbps ports
review of the user requirements for the number of horizontal cable drops per room and the number of total drops in any catchment area.
This includes the number of vertical cable runs. E.g.: four horizontal cable runs per room;
total 18 rooms; require 72 LAN switch ports
Collision Domain Size with Hubs
Layer 2 Switch Collision Domains
An Acceptable Solution Using Hubs
Must make sure bandwidth to the host is provided in accordance to the specifications gathered in the requirements phase of the network design process
Layer 3 Design
Layer 3 Router for Segmentation
All data traffic from Network 1 destined for Network 2 has to go through the router.
There are two broadcast domains
Logical Addressing Mapped to the Physical Network
A standard convention should be set for addresses of important hosts on the network.
Address Map and Logical Network Map
Logical Network Map Address Mapprovides a snapshot of the network
Physical Network Map
helps to troubleshoot the network
VLAN Environment
combines Layer 2 switching and Layer 3 routing technologies
limits both collision domains and broadcast domains
provides security with the creation of VLAN groups
Hierarchical LAN Designeasier to make changes to the network as the organization grows
Access layer switches
the entry point for user workstations and servers to the network
provides services such as VLAN membership. Access layer functions also include MAC layer
filtering and microsegmentation
Distribution layer
Networks are segmented into broadcast domains
Policies are applied and ACLs can filter packets.
Switches in this layer operate at Layer 2 and Layer 3
Distribution layer functions: Aggregation of the wiring closet connections Broadcast/multicast domain definition Virtual LAN (VLAN) routing Any media transitions that need to occur Security
Distribution layer
The following Cisco switches are suitable for the distribution layer: Catalyst 2926G Catalyst 5000 family Catalyst 6000 family
Core layer
The core layer is a high-speed switching backbone.
If the switch does not have a router module, an external router is used for the Layer 3 function.
This layer should not perform any packet manipulation.
A core infrastructure with redundant alternate paths gives stability to the network
Asynchronous Transfer Mode (ATM) or Ethernet switches can be used.
Core layer
The following Cisco switches are suitable for the core layer: Catalyst 6500 series Catalyst 8500 series IGX 8400 series Lightstream 1010
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