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Native vlan

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

 

 

Everyone's tags (1)
1 REPLY
Bronze

Hi,When you have following

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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