Defining VLANs

Implementing Best Practices for VLAN Topologies

Issues in a Poorly Designed Network

• Unbounded failure domains

• Large broadcast domains

• Large amount of unknown MAC unicast traffic（单播流量过大）

• Unbounded multicast traffic（组播流量多大）

• Management and support challenges（不好管理与支持）

• Possible security vulnerabilities(安全问题 )

Scalable Network Addressing

• Allocate IP address spaces in contiguous blocks.

• Allocate one IP subnet per VLAN.

IT, Human Resources Sales, Marketing Finance, Accounting

Interconnection Technologies —互联技术

Technology Use

Fast Ethernet Connects end-user devices to the access layer switch

Gigabit Ethernet

Access to distribution switch, high-use servers

10-Gigabit Ethernet

High-speed switch to switch links, backbones

EtherChannel High-speed switch to switch links, backbones with redundancy

Determining Equipment and Cabling Needs

Each link provides adequate bandwidth for traffic aggregating over that link.

VLANs and the Logical Network

Network Traffic Types

Traffic types to consider:• Network management(网络管理流量 )

• IP telephony （ ip电话流量）• Multicast（组播）• Normal data（正常数据流）• Scavenger class（清道夫流量）

Traffic Path for IP Telephony

Consider complete traffic path when placing equipment and configuring VLANs.（使用设备与配置 vlan使要仔细考虑）

Traffic Path for IP Multicast

Consider complete traffic path when placing equipment and configuring VLANs.

Summary

• Poorly designed networks can lead to large broadcast domains.

• A hierarchical IP addressing scheme scales well in the Campus Infrastructure module.

• The interconnection technology used depends on the amount of traffic the link must carry.

• Select the best equipment, cabling, and interconnection technologies to connect devices.

• VLANs should map to the IP hierarchy for the Campus Infrastructure module.

• Separate voice and data VLANs are recommended.