Cisco Systems RJ-45-to-AUX manual Vlan Trunking Protocol VTP, LAN Emulation Lane

∙High bit of source address (HSA)—The 3−byte manufacturer’s portion of the SA field or vendor field of the source port’s MAC address.

∙15−bit descriptor—Used to distinguish the frame from other VLANs or colors. 10 bits are used to indicate the source port.

∙Bridge Protocol Data Units (BPDU) bit—Used to indicate Spanning Tree Protocol (STP) or Cisco Discovery Protocol (CDP) topology information.

∙16−bit index value—Used to indicate the port address. This index can be set to any value and may be used for diagnostic purposes only.

∙Reserved field—Used only by FDDI and Token Ring. In Token Ring, the Frame Control (FC) and Token Ring AC bits (AC) fields are placed in the header. For FDDI, the FC is placed in the field. For Ethernet, the field includes all zeros.

LAN Emulation (LANE)

LANE is an IEEE standard for transporting VLANs over networks utilizing ATM. It uses no encapsulation or tagging. This process will be covered in detail in Chapter 8.

VLAN Trunking Protocol (VTP)

From the name of this protocol, you might think it is used to create trunk links. Sorry—the closest it gets to trunk links is sending its VTP information between switches by using a trunk port between the switches and routers. VTP was created by Cisco to manage and distribute VLAN configuration information across a switched internetwork. When you configure VTP on all of your switches and assign them to the same VTP domain name, you can merely configure one switch to make changes on all the switches—the changes will be propagated to all the other switches in the network. Not only can you add VLANs, but you can delete and rename VLANs as well; the new configuration will be propagated to all the switches.

VTP maintains consistent VLAN configurations throughout the network by propagating the VLAN mapping scheme of the VTP domain across the network using many different physical media types. VTP provides for plug−and−play−type connections when you add additional VLANs. It also provides tracking, monitoring, and reporting of VLANs in the network.

In order to allow VTP to manage your VLANs across the switched internetwork, you must first designate one or more of your Cisco switches as a VTP server. All the VTP servers that need to share VLAN information must use the same domain name, and a switch can only be a member of one VTP domain. A switch configured as a server can only share VTP configuration information with switches configured as members of the same VTP domain.

VTP is used to avoid situations in which security violations occur when VLANs cross−connect and thus produce duplicate names on the network. This duplication results in a disconnection, particularly when VLANs are connected from one physical media type to another.

On Cisco Catalyst switches, the default configuration places VTP in non−secure mode. This allows other switches in the network to join the VTP domain at will and either use the domain’s configuration information or make changes to the configuration. To ensure that other switches do not join your domain without your knowledge, and to avoid security violations that can occur when inconsistent VLAN configurations reside on the network (caused when VLANs cross−connect using duplicate names on the network), you need to configure a secure mode password for your VTP management domain. The management domain name can be up to 32 characters long. You must also provide a password to place the switches in secure mode; the password can be from 8 to 64 characters long.

Note	A switch can be a member of only one VTP management domain. All the switches in the
	domain must share the same VTP domain name.

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