configuring unused nativ vl on router

[sumerfat]

for this network

 the instructor wants to configure unused vl as native , on Sw1 g0/1 , sw2 g0/1 and g0/2 , he simply configures vl 1001 as native , but when talking about the router he configures vl 10 : 

 does it mean we can't configure unused native vl on a router? how could it be 1001 on the switches but 10 on tje router , shouldn't be the same native overall.

[David Ruess]

Hello,

When configuring the Native VLAN whether it be from a SW to another SW or a Router to a SW it needs to be the same. Your instructor may be using 2 different examples and possible merging them together which makes it confusing. The switch connections can have one native VLAN between them and the SW02 and router can have another Native VLAN between them. As long as the connected devices match their native VLAN you wont have issues. You can even configure a native VLAN on a trunk port and not even allow it so every VLAN is tagged across the trunk no matter what.

Hope that helps

-David

[ilhambasuki]

If you configured ip address on physical interface like in the picture, all packet from router will be bundled in ethernet frame on switch as VLAN 1001, since it is the native / untagged VLAN.

If you want to make it in VLAN 10, you can try:
1. Change native vlan on switch to VLAN 10

2. Configure sub-interface on router with dot1q 10

[sumerfat]

ok, but in this case it won't be unused vlan, the idea here is about using unused native vlan, in switches he already made native unused vl 1001, while the used are 10, 20, 30

[ilhambasuki · Accepted solution]

Hi,

I assume you have this configuration on your router

interface g0/0
ip address 192.168.1.62 255.255.255.192
!
interface g0/0.20
encapsulation dot1q 20
ip address 10.0.0.65 255.255.255.192
!
interface g0/0.30
encapsulation dot1q 30
ip address 10.0.0.129 255.255.255.192

If true, your instructor is correct. Router physical interface's ip address will use native vlan configured on switch. The rest sub-interface will use corresponding vlan.

Return to your original question:
- does it mean we can't configure unused native vl on a router?

Answer: We can. If you want to configure unused native vlan in sub-interface, you configure: encapsulation dot1q 1001 native

- how could it be 1001 on the switches but 10 on tje route

Answer: Actually, as I stated before, if you configure physical interface on router it will works like normal NIC on you computer or laptop. Their traffic will be untagged, and on switch, all of untagged traffic will be assigned to native VLAN for that port (in this case vlan 1001).

The result of this behaviour is subnet 192.168.1.62/26 on your network will be available on vlan 1001, not vlan 10. Logically, there is no more vlan 10 on your router.

[Gopinath_Pigili]

Native vlan must be same between the devices...Switch to Switch or Switch to Routers. To avoid any issues....configure same valn as native in all devices. Both the switches...create new vlan for example vlan 100 make it as native ....execute  following commands on both switches...

Switch(config)# vlan 100

Switch(config-vlan)# name Native

Switch(config)# Interface Gig0/1

Switch(config-if)# switchport mode trunk

Switch(config-if)#switchport trunk native vlan 100

Switch(config-if)# switchport trunk allowed vlan 10,20,30,100

For inter-valn communication...In Router...You can configure a sub-interface.....Sub-interface number you can use any number.

Router(config)# interface Gig0/0

Router(config-if)# no shutdown

Router(config)# interface Gig0/0.100

Router(config-subif)# encapsulation dot1q 100

Router(config-subif)# ip address  x.x.x.x  x.x.x.x

Best regards
******* If This Helps, Please Rate *******

[sumerfat]

ok, for the switches just clreat vl 100 and configure it as native, but on the router it needs IP address , what Ip adress could be assigned since for the used vlans 10, 20, 30 the  assigned ip addresses on the router already are the default gateway for each subnet, but for the Gig0/0.100 there is no subnet

[Gopinath_Pigili]

According to your topology...you have used 10.0.0.0/26 for vlan 10, 10.0.0.64/26 used for vlan 20, 10.0.0.0/128 used for vlan 30. Threre is one more subnet is left 10.0.0.0/192 ? You can use it for Native vlan .

Best regards
******* If This Helps, Please Rate *******