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Cisco Networking Academy

Cisco Networking Academy. Version 3.0 Module 9 VLAN Trunking Protocol George Karnbauer, CCNA. Trunking. Trunking . A trunk is a physical and logical connection between two switches across which network traffic travels. Trunking Concepts.

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  1. Cisco Networking Academy Version 3.0 Module 9 VLAN Trunking Protocol George Karnbauer, CCNA

  2. Trunking

  3. Trunking • A trunk is a physical and logical connection between two switches across which network traffic travels.

  4. Trunking Concepts • A trunk may be a physical or logical connection between devices. • A trunk is a point-to-point link capable of supporting multiple VLAN’s. • Trunking will bundle multiple virtual links over one physical link by allowing the traffic for several VLAN’s to travel over a single cable between the switches.

  5. Trunking Operation • Two main methods are used to enable trunking: • Cisco proprietary protocol, Inter-Switch Link (ISL) • IEEE 802.1q • Both use frame-tagging to identify multiple VLAN information to pass on a single trunk link.

  6. IEEE 802.1q • IEEE 802.1q is the open standard Trunking protocol used by most switches. • Places a unique identifier in the header to identify which VLAN a frame is communicating on. • The ID is removed when the frame reaches it’s final switch destination.

  7. Inter-Switch Link (ISL) • Cisco’s proprietary method of frame-tagging. • Encapsulates the Ethernet frame with information that contains the VLAN ID. • Only used on Cisco devices.

  8. Trunking Implementation • To implement Trunking, the following steps must be taken: • Configure port as a trunk port. • Switch1(config-if) switchport mode trunk • Specify port encapsulation method • Switch1(config-if) switchport trunk encapsulation dot1q • Verify trunking is enabled. • Switch1# Show Trunk

  9. VLAN Trunking Protocol-VTP

  10. VTP • VLAN Trunking Protocol (VTP) was created to solve operational problems in a switched network with VLAN’s.

  11. VTP • VTP is a messaging protocol that uses Layer 2 trunk frames to manage the addition, deletion, and renaming of VLAN’s on a single domain.

  12. VTP • VTP allows for centralized changes that are communicated to all other switches in the network. • VTP messages are encapsulated in either Cisco proprietary Inter-Switch Link (ISL) or IEEE 802.1Q protocol frames, and passed across trunk links to other devices.

  13. Benefits of VTP • VTP has the following benefits: • Configuration consistency across the network. • Ability to trunk across mixed media networks. • Reduces complexity of managing and monitoring VLAN’s across the network.

  14. VTP Trunks • Switch ports can be assigned to VLAN’s or as Trunk ports. • To assign a switch port to a VLAN; • Switch1(config-if)switchport mode access • To assign a switch port as a trunk port; • Switch1(config-if)switchport mode trunk

  15. Switch Port Assignment • While switch ports are normally assigned to only one VLAN, trunk ports, by default, carry data from all VLAN’s.

  16. VTP Operation • A VTP domain is made up of one or more interconnected devices that share the same VTP domain name. • A switch can be in one VTP domain only.

  17. VTP Switch Modes • A VTP switch can operate in one of three modes: • Server • Client • Transparent

  18. VTP Server Mode • VTP servers can create, modify, and delete VLAN and VLAN configuration parameters for the entire domain. • VTP servers save VLAN configuration information in the switch NVRAM. • VTP servers send VTP messages out to all trunk ports.

  19. VTP Client Mode • VTP clients cannotcreate, modify, or delete VLAN information. • The only role of VTP clients is to process VLAN changes and send VTP messages out all trunk ports.

  20. VTP Transparent Mode • Switches in VTP transparent mode forward VTP advertisements but ignore information contained in the message.

  21. VTP Transparent Mode • A transparent switch will not modify its database when updates are received, nor will the switch send out an update indicating a change in its VLAN status • Except for forwarding VTP advertisements, VTP is disabled on a transparent switch.

  22. VLAN Implementations • A switch will advertise its: • Management Domain • Revision Number • VLAN’s it knows about • In small networks, most switches will be set as servers. • Each switch will send this information every five minutes

  23. VLAN Implementations • VTP Advertisements are sent via multicast. • Each has a revision number assigned. • When a switch sends an advertisement with new information, it increases the revision number by 1. (N+1)

  24. VTP Advertisements • Types of VTP advertisements: • Advertisement requests • Summary advertisements • Subset advertisements

  25. Advertisement Requests • When a new device is booted, an advertisement request is generated. • A server will then respond with a summary advertisement or a subset advertisement.

  26. Summary Advertisement • Sent every five minutes. • List current revision number. • If revision is same as client, it stops. • If revision number is higher, client requests subset advertisement.

  27. Subset Advertisement • Subset advertisements contain detailed information about VLAN’s such as VTP version type, domain name and related fields, and the configuration revision number.

  28. Subset Advertisement • The following trigger these advertisements: • Creating or deleting a VLAN • Suspending or activating a VLAN • Changing the name of a VLAN • Changing the maximum transmission unit (MTU) of a VLAN • A newly created VLAN will not be advertised until ports are assigned to it.

  29. VTP Configuration

  30. VTP Configuration • To configure VTP the following must be done: • Determine the VTP domain name, Devices on different VTP domains do not communicate VTP information • Determine VTP Version 1 or 2, 1 is default • Choose VTP mode of operation

  31. VTP Configuration • To change the VTP version issue the following command: • Switch1#Vlan database • Switch1(VLAN)#vtp v2-mode • For the first switch configured, setup the VTP domain name: • Switch1(VLAN)#VTP Domain (Name)

  32. VTP Configuration • To setup switch as VTP Server: • Switch1(VLAN)# vtp server • When adding a new switch to a VTP domain, first check the existing revision number. Make sure new switch has a lower revision number. • Switch1#Show vtp status

  33. Inter VLAN Communications • Hosts on one VLAN can only communicate directly with other devices on the same VLAN. • All devices on a VLAN should be part of the same IP subnet. • If a host on one VLAN wants to communicate to a host on another VLAN, it must go through a router.

  34. Inter VLAN Communications • It is possible to have a physical connection for each configured VLAN. • This topology does not scale well. • This topology wastes connections.

  35. Inter VLAN Communications • Using sub interfaces and a trunked link allow multiple VLAN’s to run on a single link, reducing the number of ports and wire runs required.

  36. Sub-Interface Configuration • To define sub-interfaces on a physical interface, perform the following tasks: • Identify the interface. • Define the VLAN encapsulation. • Assign an IP address to the interface

  37. Sub-Interface Configuration

  38. Sub-Interface Configuration • When configuring sub-interfaces, the interface address must be a part of the subnet assigned to the VLAN.

  39. VTP Troubleshooting • Switches can only be assigned to one management domain. • Sub-interfaces must be part of the IP subnet assigned. • VTP version numbers must be the same for all switches in a VTP domain.

  40. VTP Troubleshooting • When new switches are brought into a Management domain, the revision number must be lower the current revision number.

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