Online Courses
CCNA 200-301
Online Courses
CCNA 200-301
  • Introduction
  • Interfaces And Cables
    • Ethernet
    • UTP Cables
    • Fiber Optic
    • UTP vs Fiber-Optic
    • Quiz
  • OSI Model & TCP/IP Suite
    • Networking Model
      • OSI Model
        • Application
        • Presentation
        • Session
        • Transport
        • Network
        • Data Link
        • Physical
      • PDUs
      • TCP/IP Suite
    • Quiz
  • Intro to the CLI
    • What is a CLI
      • Global Configuration Mode
      • Enable Password
    • Configuration Files
    • Canceling commands
    • Quiz
  • Ethernet LAN Switching
    • Local Area Network (LAN)
    • MAC Address
    • Ethernet Frame
    • Quiz 1
    • ARP
    • Ping
    • Quiz 2
  • IPv4 Addressing
    • Network Layer Review
    • IPv4
    • Quiz
    • Cisco CLI
    • Quiz
  • Switch Interfaces
    • CLI
    • Full/Half Duplex
    • CSMA/CD
    • Speed / Duplex Auto-Negotiation
    • Interface Errors
    • Quiz
  • IPv4 Header
    • Fields
      • Do Not Fragment
    • Quiz
  • Static Routing
    • Topology
    • CLI
    • Default Route
    • Static Route
    • Most Specific Matching Route
    • Quiz
  • Subnetting
    • Subnetting
    • Quiz
    • Variable-Length Subnet Masks
  • VLANs
    • What is a LAN ?
    • VLAN Configuration
    • Quiz 1
    • Example
    • Trunk Ports
      • Configuration
    • VLAN Ranges
    • Native VLAN
    • Router on a Stick (ROAS)
    • Quiz 2
    • Native VLAN on Router
    • Layer 3 (Multilayer) Switches
    • Quiz 3
  • DTP/VTP
    • DTP
    • VTP
    • Quiz
  • Spanning Tree Protocol
    • Network Redundancy
    • Layer 2 Loops
    • Spanning Tree Protocol
      • Exercise
    • STP Port Role Selection
      • Exercise
    • Blocking Ports
    • Quiz 1
    • States
    • Timers
    • BPDU
    • STP Toolkit
    • Configurations
    • Load-Balancing
      • Quiz
    • Quiz 2
  • Rapid Spanning Tree Protocol
    • STP Version Comparison
    • RSTP Intro
    • Quiz 1
    • BPDU
    • Link Types
    • Quiz 2
  • EtherChannel
    • Why EtherChannel is needed?
    • Load-Balancing
      • Configuration
    • PAgP, LACP, and Static
      • PAgP
      • LACP
      • Static
      • Manually Configure the Negotiation Protocol
    • EtherChannel Requirements
    • EtherChannel Verification
    • Layer 3 EtherChannel
    • Quiz
  • Dynamic Routing
    • Network Topology
    • Dynamic Routing
    • Types
      • Distance Vector Protocols
      • Link State Protocols
    • Metrics
    • Administrative Distance
      • Floating Static Routes
    • Quiz
    • RIP
      • RIPv1 & RIPv2
      • RIP Configuration
    • EIGRP
      • EGRP Configuration
    • Quiz
    • OSPF
      • Areas
      • Configuration
      • Cost
      • Neighbors
      • Loopback Interfaces
      • Network Types
      • Neighbor Requirements
      • LSA Types
    • Configuration
    • Quiz
  • First Hop Redundancy Protocols
    • Introduction
    • HSRP
    • VRRP
    • GLBP
    • Comparing FHRPs
    • Configuring HSRP
    • Quiz
  • TCP & UDP
    • Basic of Layer 4
      • Port Numbers / Session Multiplexing
    • TCP
    • UDP
    • Comparing TCP & UDP
    • Port Numbers
    • Quiz
  • IPv6
    • What about IPv5?
    • Why IPv6?
    • IPv6
    • Identifying the IPv6 Prefix
    • Configuration
    • EUI-64
      • Configuration
    • Why invert the 7th bit?
    • Global Unicast Addresses
    • Unique Local Addresses
    • Link Local Addresses
    • Multicast Addresses
    • Anycast Addresses
    • Other IPv6 Addresses
    • Representation
    • Header
    • Solicited-Node Multicast Address
    • Neighbor Discovery Protocol
      • SLAAC
      • Duplicate Address Detection (DAD)
    • IPv6 Static Routing
    • Quiz
  • Access Control Lists
    • What are ACLs?
    • How ACLs work
    • Implicit Deny
    • ACL Types
    • Standard Numbered ACLs
    • Standard Named ACLs
    • Numbered ACLs With Subcommands
    • Resequencing ACLS
    • Extended ACLs
    • Quiz
  • Layer 2 Discovery Protocols
    • Introduction
    • Cisco Discovery Protocol
    • Link Layer Discovery Protocol
    • Quiz
  • Network Time Protocol
    • The importance of time
    • Manual Time Configuration
    • Network Time Protocol
    • Reference Clocks
    • NTP Hierarchy
    • NTP Configuration
    • NTP Server mode
    • Symmetric active mode
    • NTP Authentication
    • Quiz
  • Domain Name System
    • Purpose of DNS
    • DNS Cache
    • DNS in Cisco IOS
    • Quiz
  • Dynamic Host Configuration Protocol
    • Purpose of DHCP
    • DHCP Messages
    • Relay
    • DHCP Sever configuration in IOS
    • Quiz
  • Simple Network Management Protocol
    • SNMP
    • Versions
    • Messages
    • Configuration
    • Quiz
  • Syslog
    • Syslog
    • Message Format
    • Logging Locations
    • Configuration
    • Syslog vs SNMP
    • Quiz
  • Secure Shell
    • Page
    • Console Port Security
    • L2 Switch Management IP
    • Telnet
    • SSH
    • Quiz
  • FTP & TFTP
    • FTP and TFTP
    • Trivial File Transfer Protocol
    • File Transfer Protocol
    • FTP vs TFTP
    • IOS File Systems
    • Upgrading Cisco IOS
    • Quiz
  • Network Address Translation
    • Private IPv4 Addressess
    • Network Address Translation (NAT)
    • Static NAT
    • Configuration
    • Dynamic NAT
    • Configuration
    • PAT (NAT Overload)
    • Quiz
  • Quality of Service
    • IP Phones
    • Power over Ethernet (PoE)
    • Quality of Service (QoS)
    • Queuing
    • Classification
    • IP Precedence and DSCP
    • RFC 4954
    • Trust Boundaries
    • Queuing/Congestion Management
    • Shaping and Policing
    • Classification
    • Quiz
  • Security Fundamentals
    • Why Security?
    • Concepts
    • Denial-of-service Attack
    • Spoofing Attacks
    • Reflection/Amplification Attacks
    • Man-in-the-middle Attack
    • Reconnaissance Attacks
    • Malware
    • Social Engineering Attacks
    • Password-related attacks
    • Multi-factor Authentication
    • Digital certificates
    • Controlling and Monitoring Users with AAA
    • Security Program Elements
    • Quiz
  • Port Security
    • Port Security
    • Why Port Security?
    • Enabling Port Security
    • Violation Modes
    • Secure MAC Address Aging
    • Sticky Secure MAC Addresses
    • Quiz
  • DHCP Snooping
    • DHCP Snooping
    • DHCP Starvation
    • DHCP Poisoning (Man-in-the-Middle)
    • DHCP Messages
    • DHCP Snooping Operations
    • DHCP Snooping Rate-Limiting
    • DHCP Option 82 (Information Option)
    • Quiz
  • Dynamic ARP Inspection
    • Gratuitous ARP
    • DAI
    • ARP Poisoning (Man-in-the-Middle)
    • Operations
    • Configurations
    • Optional Checks
    • ARP ACLs
    • Quiz
  • LAN Architectures
    • Common Terminologies
    • Two-Tier Campus LAN Design
    • Three-Tier Campus LAN Design
    • Spine-Leaf Architecture
    • SOHO Networks
    • Quiz
  • WAN Architectures
    • WAN
    • Leased Lines
    • MPLS
    • Internet Connections
    • Redundant Internet Connections
    • Internet VPNs
      • Site-to-Site VPNs (IPsec)
      • Remote-Access VPNs
    • Quiz
  • Virtualization & Cloud
    • Server Hardware
    • Servers before Virtualization
    • Virtualization
    • Why Virtualization
    • Connecting VMs to the Network
    • Cloud Services
    • Five Essential Characteristics of Cloud
    • Three Service Models of Cloud
    • Four Deployment Models of Cloud
    • Benefits of Cloud Computing
    • Connecting to Cloud Resources
    • Quiz
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On this page
  • Tagging
  • Protocols
  • 802.1Q Tag
  • TPID
  • TCI
  1. VLANs

Trunk Ports

In a small network with few VLANs, it is possible to use a separate interface for each VLAN when connecting switches to switches, and switches to routers.

However, when the number of VLANs increases, this is not viable. It will result in wasted interfaces, and often routers won't have enough interfaces for each VLAN.

You can use trunk ports to carry traffic from multiple VLANs over a single interface.

Tagging

Switches will 'tab' all frames that they send over a trunk link. This allows the receiving switch to know which VLAN the frame belongs to.

  • Trunk ports = tagged ports.

  • Access ports = untagged ports.

Protocols

There ate two main trunking protocols: ISL (Inter-Switch Link) and IEEE 802.1Q.

ISL is an old Cisco proprietary protocol created before the industry standard IEEE 802.1Q.

IEEE 802.1Q is an industry standard protocol created by the IEEE (Institute of Electrical and Electronics Engineers).

Note

You will probably NEVER use ISL in the real world. Even modern Cisco equipment doesn't support it. For the CCNA you only need to learn 802.1Q.

802.1Q Tag

The 802.1Q tag is inserted between the Source and Type/Length fields of the Ethernet frame.

The tag is 4 bytes (32 bits) in length.

The tag consists of two main fields:

  • Tag Protocol Identifier (TPID);

  • Tag Control Information (TCI).

The TCI consists of three sub-fields.

TPID

16 bits (2 bytes) in length

Always set to a value of 0x8100. This indicates that the frame is 802.1Q-tagged.

TCI

PCP - Priority Code Point

3 bits in length

Used for Class of Service (CoS), which prioritizes important traffic in congested networks.

DEI - Drop Eligible Indicator

1 bit in length

Used to indicate frames that can be dropped if the network is congested.

VID - VLAN ID

12 bits in length

Identifies the VLAN the frame belongs to.

12 bits = 4096 total VLANs, range of 0 - 4095.

VLANs 0 and 4095 are reserved and can't be used.

Therefore, the actual range of VLANs is 1 - 4094.

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Last updated 2 years ago