- ISL is an Cisco proprietary protocol.
- Supports up to 1000 Vlans
- Original frame is encapsulated and a new header is inserted during encapsulation process.
- A 26 byte header and a 4 byte FCS (frame check sequence) are inserted. Hence a total of 30 Bytes of overhead.
- ISL tags frames from native Vlans.
- ISL is less preferred in networks because of its high overhead value which is added to each Ethernet frame.
- It is an IEEE Standard.
- 802.1q supports 4096 Vlans.
- In 802.1q encapsulation process, a 4 byte tag is inserted into original frame and FCS (Frame Check Sequence) is re-calculated.
- 802.1q does not tag frames from native Vlans.
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