VLANS Flashcards
LAN Designs
• The campus LAN should be designed for scalability, performance and security
To aid in a best practice design process, the network topology is split into access, distribution and core layers
The layers have their own design principles and characteristics
The Access Layer
• End hosts such as desktop computers, servers and IP phones connect into the network at the access layer
• It is designed to have a high port count at an affordable cost
• Desktops typically have only one Network Interface Card (NIC) so they connect into one switch or Wireless Access Point
• Servers will often have dual NICs and connect to a pair of redundant switches
• client access security measures are enabled at the Access Layer
The Distribution Layer
• Access Layer switches uplink to Distribution Layer switches
• The Distribution Layer switches serve as an aggregation point for the Access Layer and provide scalability
• Distribution Layer switches are typically deployed in redundant pairs, with downstream Access Layer switches connected to both
• End hosts are not typically connected here
• Most software policy such as Qos is enabled at this laver
The Core Layer
• Distribution Layer switches uplink to Core Layer switches
• Core Layer switches are typically deployed in redundant pairs, with downstream Distribution Layer switches connected to both
• Traffic between different parts of the campus travels through the core so it is designed for speed and resiliency
• Software policy slows the switch down so should be avoided in the
Core Layer
Collapsed Distribution and Core
• Smaller campuses do not need the scalability of three separate layers
• In these cases a Collapsed Distribution and Core layer is used, where the Distribution and Core layer functions are performed on the same hardware device
Spine-Leaf Data Center Design
Tier 1 - Leaf
Tier 2 - Spine
Router Operations
• Routers operate at Layer 3 of the OSI stack
• Hosts in separate IP subnets must send traffic via a router to communicate
• Security rules on routers or firewalls can be used to easily control what traffic is allowed between different IP subnets at Layer 3
• Routers do not forward broadcast traffic by default
• They provide performance and security by splitting networks into smaller domains at Layer 3
Switch Operations
• Switches operate at Layer 2 of the OSI stack
• They do forward broadcast traffic by default
• By default a campus switched network is one large broadcast domain
• Switches flood broadcast traffic everywhere, including between different IP subnets
• This raises performance and security concerns
Broadcast traffic problem in switch
B
