Link Protocols for Carrying Multiple VLANs

BD

Cisco switches can use two different encapsulation types for trunks, the industry standard 802.1q or the Cisco proprietary ISL. Generally, most network engineers prefer to use 802.1q since it is standards based and will interoperate with other vendors.

The two link protocols that are used to carry multiple VLANs over a single link are 802.1q and ISL.

802.1q is an IEEE standard that allows for VLAN tagging of Ethernet frames. It adds a 4-byte VLAN tag to the Ethernet frame, which includes information such as the VLAN ID. This tag allows multiple VLANs to be carried over a single link.

ISL, on the other hand, is a Cisco proprietary protocol that also allows for VLAN tagging of Ethernet frames. It adds a 26-byte header to the Ethernet frame, which includes information such as the VLAN ID. ISL has been largely replaced by 802.1q, which is a standardized protocol.

VTP (VLAN Trunking Protocol) is not a link protocol but rather a protocol used for VLAN management. It allows for the propagation of VLAN information across multiple switches in a network.

IGP (Interior Gateway Protocol) is a protocol used for routing within a single autonomous system (AS).

802.3u is a standard that defines Fast Ethernet (100 Mbps) over twisted pair cabling. It does not have any VLAN tagging capabilities.