Switch unable to ping router

[NaderHussain]

I have a switch and router on Packet Tracer and I cannot ping the router from the switch. Below, is the interface script on the switch and the router's f0/0 configuration.

Configs:

Router:

 interface FastEthernet0/0
ip address 192.168.20.1 255.255.255.0
duplex auto
speed auto
!

(f0/0 is Up)

Switch:

interface FastEthernet0/1

switchport trunk native vlan 99

switchport trunk allowed vlan 1,20

switchport mode trunk

switchport nonegotiate

!

Why is the switch unable to connect to the router?

interface Vlan1
ip address 192.168.20.2 255.255.255.0
!
ip default-gateway 192.168.20.1
!

[Meheretab Mengistu]

Please share the output of the following commands:  sh vlan bri, sh int trunk and sh int vlan1. I guess the SVI (interface vlan1) is up/down because there is nothing connected to the switch.

HTH,

Meheretab

[jalejand]

Your trunk link towards the Router is using vlan 99 as native vlan. This means that frames from vlan 99 will become untagged and frames from vlan 1 will have a dot1q tag on it.

The router interface expects untagged packets on fa0/0, configure a subinterface matching dot1q to accept packets from vlan 1.
interface fa0/0.1
encapsulation dot1q 1
ip add 192.168.20.1 255.255.255.0
no shut

and then leave fa0/0 with no Ip address.

[jalejand]

Your trunk link towards Fa0/0 is using native vlan as 99, frames from vlan 99 are now untagged while vlan 1 frames will have a dot1q tag of 1.

Fa0/0 interface on the router side will process untagged frames as it has no encapsulation configured.
* Remove the native vlan 99 command from the switch to keep vlan 1 frames as untagged again
* Create a subinterface in for fa0/0 in the router matching encapsulation dot1q for vlan 1 tagged packets.