Communicating Between VLANs
Cisco IOS provides full-feature routing at Layer 3, and translation at Layer 2 between VLANs. There are three different protocols available for routing between VLANs:
Inter-Switch Link (ISL)
IEEE 802.10
ATM LAN emulation
All three of these technologies are based on OSI Layer 2 bridge-multiplexing mechanisms.
ISL Protocol
ISL protocol is used to interconnect two VLAN-capable Fast Ethernet devices, such as the Catalyst 5000 or 3000 switches and Cisco 7500 routers. The ISL protocol is a packet-tagging protocol that contains a standard Ethernet frame and the VLAN information associated with that frame. The packets on the ISL link contain a standard Ethernet, FDDI, or Token Ring frame and the VLAN information associated ...
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