Hello Renzil,
a basic QoS policy for your purpose would look like this:
class-map match-all PRIORITY
match ip address 101
!
policy-map BANDWIDTH
class PRIORITY
bandwidth 512
!
interface Serial0
service-policy output BANDWIDTH
!
access-list 101 permit ip x.x.x.x any
Your access list has to match the Vlan IP address range that you want to reserve bandwidth for. If you just want to reserve bandwidth for public addresses (the Internet), you can exclude private space addresses from your access list. In that case, prepend the following to the access list:
access-list 101 deny ip x.x.x.x 10.0.0.0 0.255.255.255
access-list 101 deny ip x.x.x.x 172.16.0.0 0.15.255.255
access-list 101 deny ip 192.168.0.0 0.0.255.255
Can you try and see if this works for you ?
Regards,
GP