Hi Munawar.
To set up a Etherchannel is easy; you just need to make sure that the ports you want to set up the channel have the exactly same config. Example:
interface FastEthernet1/0
switchport mode trunk
switchport trunk encapsulation dot1q
switchport trunk native vlan 10 (default is Vlan 1)
duplex full
speed 100
channel-group 1 mode on
So, you type the command below, to show the channel group summary:
R1#sh etherchannel 1 summary
Flags: D - down P - in port-channel
I - stand-alone s - suspended
R - Layer3 S - Layer2
U - in use
Group Port-channel Ports
-----+------------+-------------------------
1 Po1(SD) Fa1/0(D)
R1#
As simple as you see. You do not have to change any gateway settings, the Etherchannel acts as a single link and would not impact on the entire config. If you have more switches from different vendors, you can use a similar solution that is the Link Aggregation (LACP). Cisco switches use the proprietary solution, which is the Etherchannel.
Regards,
Fred.