Let me point to the answer from the difference between these two protocols :
First, ISL is a Cisco-proprietary trunking protocol, where dot1q is the business standard. (Those of you new to Cisco testing should get used to the phrases "Cisco-proprietary" and "business customary".) If you're working in a multivendor atmosphere, ISL will not be a great choice. And despite the fact that ISL is Cisco's personal trunking protocol, some Cisco switches run only dot1q.
ISL also encapsulates all the body, increasing the community overhead. Dot1q only places a header on the body, and in some cir[censored] stances, would not even do that. There may be much less overhead with dot1q as compared to ISL. That leads to the third major distinction, the way the protocols work with the native vlan.
The native vlan is just the default vlan that change ports are positioned into if they don't seem to be expressly placed into one other vlan. On Cisco switches, the native vlan is vlan 1. (This may be changed.) If dot1q is working, frames which can be going to be despatched across the trunk line do not even have a header positioned on them; the distant change will assume that any frame that has no header is destined for the native vlan.
The issue with ISL is that's does not perceive what a native vlan is. Every single body will probably be encapsulated, whatever the vlan it is destined for.
Hope this helps your
Regards.
Encapsulation is the process of giving the security to the data being transmitted between Networks.
it provides the data security my providing the header and footer to the data which contain the information about the source and destination IP address and the port numbers.
Encapsulation is the Security of Data Link layer (Layer 2) while the data being in the process of transformation, even at the Switch Trunk port it the score of providing the security to the Data(packets) getting transmitted at the ports.
