Wednesday, February 10, 2016

CCNAv2 Chapter 3 Notes - VLANs

Author's Note:
The majority of this chapter are packet tracers, which I will upload when given the time.
They will be (most likely) released this or next week.

CCNA2 Notes 

Chapter 3
VLANs (& Trunking)
VLAN Defitions
  • A VLAN is a logical partition of a layer 2 network.
  • Multiple partitions can be created, allowing for multiple vlans to co-exist.
  • Each VLAN is a broadcast domain with its own IP network.
  • VLANs are mutually isolated and packets can only pass via router.
  • The partitioning of the Layer 2 network takes place inside a layer two device, usually via switch.
  • The hosts grouped with a VLAN are unaware of the VLANs existence.
  • VLAN Trunks carry more than one VLAN.

What is a native VLAN?
Native VLANs pass untagged traffic over trunk, as well as identifies both ends of the trunk.
When native VLANs are assigned to a port, or the port is in the default port, it does not tag the frame passing over the VLAN.

How do you remove a single VLAN from a switch (or related)?
"no vlan <number>"

If there are multiple VLANs on a switch, and a device on the switch sends a broadcast message, what devices attached to the switch will receive that broadcast message?
Only the same devices in the same VLAN as the sending device will receive that broadcast message. So, for example, if a PC from VLAN 10 sends a broadcast, a secondary 

What is DTP?
Dynamic Trunking Protocol

What does DTP do?
DTP allows switches to configure either trunking or access among the network.

How would you block DTP from working?
Use "nonegotiate" on the interface to disable trunking.

VLANs are split into two categories:
  • Normal Range VLANs
    • VLAN numbers from 1 to 1005.
    • Configurations stored in vlan.dat
    • VTP can only learn and store numbers.

Using these four methods...
1. Dynamic Auto
2. Dynamic Desirable
3. Trunk
4. Access

You can enable trunking by using the following:
2 to 2 (Dynamic Desirable -> Dynamic Desirable)
2 to 1 (Dynamic Desirable -> Dynamic Auto)
2 to 3 (Dynamic Desirable -> Trunk)

Why can't you have 'dynamic auto' on both ends of a link configuration?
Given 'dynamic auto's nature, neither side will initiate trunking.

How to create a VLAN?
     -     configure terminal
  • vlan <vlan number>
    • name <vlan_name>
  • end
  • config terminal
  • interface <id>
  • ip address
  • switchport mode <access/trunk>

VLAN Design Guides

  • Move all ports from VLAN 1 and assign them to a not-in-use VLAN.
  • Shutdown all unused switch ports
  • Separate management and user data traffic
  • Change the management VLAN to VLAN other than VLAN 1
  • Ensure that only devices in the management VLAN can connect the switches
  • The switch should only accept SSH connections
  • Disable autonegotiation on trunk ports
  • Do not use auto or desirable switch port modes

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