traffic flows between the switches. With ISL, an Ethernet frame is encapsulated with a header that contains a VLAN ID. Web Links Understanding and Configuring VLAN Trunking Protocol (VTP) http://www.cisco.com/en/US/tech/
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Content 9.1 Trunking 9.1.5 Trunking implementation To create or configure a VLAN trunk on a Cisco IOS command-based switch, configure the port first as a trunk and then specify the trunk encapsulation with the following commands: Before attempting to configure a VLAN trunk on a port, determine what encapsulation the port can support. This can be done using the show port capabilities command. In the example, notice in the highlighted text that Port 2/1 will support only the IEEE 802.1Q encapsulation. Verify that trunking has been configured and verify the settings by using the show trunk [mod_num/port_num] command from privileged mode on the switch. Figure shows the trunking modes available in Fast Ethernet and Gigabit Ethernet. Lab Activity Lab Exercise: Trunking with ISL This lab is to create an ISL trunk line between the two switches to allow communication between paired VLANs. Lab Activity Lab Exercise: Trunking with 802.1q This lab is to create an 802.1q trunk line between the two switches to allow communication between paired VLANs. Lab Activity e-Lab Activity: Trunking with ISL In this lab, the student will create multiple VLANs on two separate switches, name the switches, and assign multiple member ports to the switches. Lab Activity e-Lab Activity: Trunking with 802.1q In this lab, the student will create multiple VLANs on two separate switches, name the switches, and assign multiple member ports to the switches. Web Links Understanding and Configuring VLAN Trunk Protocol (VTP) http://www.cisco.com/en/US/tech/ tk389/tk689/ technologies_tech_ note09186a0080094c52.shtml
Content 9.2 VTP 9.2.1 History of VTP VLAN Trunking Protocol (VTP) was created to solve operational problems in a switched network with VLANs. Consider the example of a domain with several interconnected switches that support several VLANs. To maintain connectivity within VLANs, each VLAN must be manually configured on each switch. As the organization grows and additional switches are added to the network, each new switch must be manually configured with VLAN information. A single incorrect VLAN assignment could cause two potential problems: With VTP, VLAN configuration is consistently maintained across a common administrative domain. Additionally, VTP reduces the complexity of managing and monitoring VLAN networks.
Content 9.2 VTP 9.2.2 VTP concepts The role of VTP is to maintain VLAN configuration consistency across a common network administration domain. VTP is a messaging protocol that uses Layer 2 trunk frames to manage the addition, deletion, and renaming of VLANs on a single domain. Further, 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. In IEEE 802.1Q frames a 4 byte field is added that tags the frame. Both formats carry the VLAN ID. While switch ports are normally assigned to only a single VLAN, trunk ports by default carry frames from all VLANs. Web Links VLAN Trunking Protocol Basics http://infocenter.cramsession.com/
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Content 9.2 VTP 9.2.3 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. When transmitting VTP messages to other switches in the network, the VTP message is encapsulated in a trunking protocol frame such as ISL or IEEE 802.1Q. Figure shows the generic encapsulation for VTP within an ISL frame. The VTP header varies, depending upon the type of VTP message, but generally, four items are found in all VTP messages: VTP switches operate in one of three modes: 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. VTP clients cannot create, modify, or delete VLAN information. This mode is useful for switches lacking memory to store large tables of VLAN information. The only role of VTP clients is to process VLAN changes and send VTP messages out all trunk ports. Switches in VTP transparent mode forward VTP advertisements but ignore information contained in the message. 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. VLANs detected within the advertisements serve as notification to the switch that traffic with the newly defined VLAN IDs may be expected. In Figure , Switch C transmits a VTP database entry with additions or deletions to Switch A and Switch B. The configuration database has a revision number that is incremented by one. A higher configuration revision number indicates that the VLAN information that is being sent is more current then the stored copy. Any time a switch receives an update that has a higher configuration revision number the switch will overwrite the stored information with the new information being sent in the VTP update. Switch F will not process the update because it is in a different domain. This overwrite process means that if the VLAN does not exist in the new database, it is deleted from the switch. In addition, VTP maintains its own NVRAM. An erase startup-configuration clears the NVRAM of configuration commands, but not the VTP database revision number. To set the configuration revision number back to zero, the switch must be rebooted. By default, management domains are set to a nonsecure mode, meaning that the switches interact without using a password. Adding a password automatically sets the management domain to secure mode. The same password must be configured on every switch in the management domain to use secure mode. Web Links VLAN Trunking Protocol Basics http://infocenter.cramsession.com/
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Content 9.2 VTP 9.2.4 VTP implementation With VTP, each switch advertises on its trunk ports, its management domain, configuration revision number, the VLANs that it knows about, and certain parameters for each known VLAN. These advertisement frames are sent to a multicast address so that all neighboring devices can receive the frames. However, the frames are not forwarded by normal bridging procedures. All devices in the same management domain learn about any new VLANs configured in the transmitting device. A new VLAN must be created and configured on one device only in the management domain. All the other devices in the same management domain automatically learn the information. Advertisements on factory-default VLANs are based on media types. User ports should not be configured as VTP trunks. Each advertisement starts as configuration revision number 0. As changes are made the configuration revision number is increased incrementally by one, (n + 1). The revision number continues to increment until it reaches 2,147,483,648. When it