Cisco Systems RJ-45-to-AUX manual InterVLAN Routing, Methods for Vlan Identification, Server Mode

Server Mode

Server mode, which is configured by default, allows you to create, modify, and delete VLANs for the management domain. Configuration changes are then sent to all other participating members of the VTP domain. At least one VTP server should exist in the VTP management domain. Two or more switches can be configured as servers for redundancy. When a server’s power is cycled, the switch configured as a server maintains its global VLAN information.

Transparent Mode

Transparent mode allows VTP switches to be configured to not accept VTP information and to merely forward advertisements the switch receives to other switches participating in the VTP domain. Even though switches configured for transparent mode will still send VTP information and advertisements, they will not update their databases or send out information on VLAN or topology changes. In this mode, switches do not participate in any VTP functions, such as sending VTP advertisements or synchronizing VLAN information. VTP version 2 does allow a switch operating in transparent mode to forward the advertisements it receives out any configured trunk ports, thus allowing other switches participating in VTP to obtain the advertisements.

Methods for VLAN Identification

To logically identify which packets belong to which VLAN or VLAN group, Cisco Catalyst switches support many trunking protocols to put a header on frames. The headers identify the VLAN associated with the frame; each switch in the switch block removes the header before the frame exits the access link port or ports belonging to the identified VLAN.

Dynamic Trunking Protocol

The Dynamic Trunking Protocol (DTP) is another way of allowing trunk links to carry VLAN tagged frames across multiple switches or routers. DTP manages trunk negotiation in the Catalyst Supervisor Engine software releases 4.2 and later.

With previous versions of the Catalyst Supervisor Engine software, trunk negotiation was managed by the Dynamic Inter−Switch Link (DISL) protocol. Version 4.1 of the Catalyst Supervisor Engine software allows DISL auto−negotiation of ISL trunks only. In this version, you can manually configure DISL to auto−negotiate IEEE 802.1Q trunks.

In versions 4.2 and later, DTP supports and manages IEEE 802.1Q and ISL trunk links.

Warning	If you have non−DTP−compatible networking devices on the network, you might
	want to disable this feature because non−DTP internetworking devices forward DTP
	frames improperly. When you disable DTP, the link still can become a trunk, but
	DTP frames will no longer be generated.

InterVLAN Routing

Access layer switches occupy the same place in the network as hubs. However, unlike hubs operating at Layer 1, switches examine the frames at Layer 2 and try to process the frames. A hub simply repeats the data to every single port, whereas a switch filters the data and forwards it directly to the destination port if the destination does not require routing. If data arrives on a port assigned to a VLAN and the destination is unknown, the switch repeats the signal only to the port or ports assigned to the VLAN, except for the port of arrival.

The switch also has the ability to regenerate packets, enabling the data to be forwarded even greater distances

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