What is the need of Native VLAN and default VLAN. How they are related? Can Somebody explain this in detail?
The default VLAN in a switch is the one applied to ports when their configuration is reset, for instance when you remove a port from a LAG trunk, or a new port module is inserted in a chassis.
The native VLAN of a trunk port is the one that is forwarded and accepted without tag. Often, a VLAN trunk port has all VLANs tagged.
With default switch configuration native vlan and default vlan are the same - vlan 1. You can configure native vlan to use any vlan if you want to and default vlan is always vlan 1, you can't change this.
Native vlan is needed to accept traffic without vlan tag on the trunk port, after receiving traffic without vlan tag switch would add native vlan tag to that traffic. By default it adds vlan 1 tag(default vlan).