03-20-2014 09:08 PM - edited 03-07-2019 06:48 PM
Hi,
I have a query on Native vlan.
Here is the topology
Router 1 (e0/0) ------ (f0/1)SW1 (f0/2) ------ (f0/2) SW2 (f0/1) ------(e0/0) Router 2
Necessary configuration on the devices
Router 1
int e0/0.100
encapsulation dot1Q 100
ip address 10.0.0.1 255.255.255.252
SW1
int f0/1
switchport trunk encapsulation dot1q
switchport mode trunk
int f0/2
switchport trunk encapsulation dot1q
switchport mode trunk
SW2
int f0/2
switchport trunk encapsulation dot1q
switchport mode trunk
int f0/1
switchport access vlan 100
switchport mode access
Router 2
int e0/0.100
encapsulation dot1Q 100
ip address 10.0.0.2 255.255.255.252
Obeservations
# With the above configuration i am not able to ping 10.0.0.1 from router 2
# Changing port f0/1 on switch 2 from access to trunk port resolve the issue , which i can understand
# hoverver If i set native vlan as 100 on router 2 (encapsulation dot1Q 100 native ) , i am able to ping . I am not able to understand why this happens
Any help on this is highly appreciated ..
Thanks
MS
03-20-2014 11:07 PM
Hi,
When you have following,
int f0/1
switchport access vlan 100
switchport mode access
Swithc will untagg all vlan 100 traffic as it goes out that inerface "UNTAGGED" traffic.
on router 2 ,you have your IP address on VLAN 100. Which means that if you want to access that IP address, the packets should enter the router as TAGGED VLAN100 traffic. which will not work because your switch UNTAGs them as it leavs the port.
When you configure your router with the NATIVE VLAN 100 command, we basically instruct the router to consider the UNTAGGED traffic comming in from that port as VLAN 100 traffic". Think of this as if the router is accutally tagging incoming UNTAGGED traffic as TAGGED VLAN 100 traffic as it enters this interface.. so this is why it works when you have the switch port access command on the switch
Hope this helps..
please rate the hlepful posts.. :)
Thanks
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