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SchinkelA
Beginner

Removing vlan tagging after trunking?

I'm attempting to bridge two locations.
One is on the third floor of the building with a number of vlans.
The other is in the basement (a C4948).

I want to trunk the vlans from the third floor down to the basement.

Once they are trunked down there, I want to split each vlan up to its own switch and remove the tagging..

Problem is I am unsure how to go about this.
Is it simply to configure a native vlan on one port that connects to the trunked switch, and the native vlan trunk will untag the packets so nothing in the servers will need to be configured to recognize the vlans?

1 ACCEPTED SOLUTION

Accepted Solutions

Switch A fas0/0------trunk ------ fas0/0 Switch B ---------computer A

                                                                   |----------Computer B

Vlans X, Y and Z

in both switches

fas0/0

sw trun en dot

sw mo trunk

sw trunk allo vlan X Y Z

802.1Q has the concept of Native VLAN, untagged traffic received in any port will be assumed to be part of it. Once the traffic reaches Switch B, the tag will be removed and the it will be forwarded through the interfaces that belong to specific vlans

View solution in original post

7 REPLIES 7
Roman Rodichev
Rising star

You can configure the ports that go to individual switches in the basement like this:

int inerfacex/x

switchport mode access

switchport access vlan X

or like this

int interfacex/x

switchport trunk enap dot1q

switchport mode trunk

switchport trunk native vlan X

switchport trunk allowed vlan X

Thank you Roman, I am aware of access mode and trunking with allowed lists.

I want to take all the VLANs in Site A that connect to Switch A,
Trunk Switch A to Switch B,
In Site B, I want to take the VLANS that were trunked into Switch B and send them out to their own individual switches on a per-vlan basis (using access mode / allow lists),
Then on those individual switches I need all servers that hook into it to be able to use the network anywhere in Site B or Site A.

Am I just overthinking this and any trunk configured with the native VLAN option will not only tag the outgoing untagged traffic, but sumarily untag the 'native tagged' traffic when it comes back in?

Thank you,

Are you saying you want hosts on those 3 switches to be in the same IP subnet and have access to each other, and at the same time have access to the top floor devices in the appropriate VLANs?

If i understand correctly then yes you are over thinking it

It has nothing to do with the native vlan. Simply connect the 2 switches together with a trunk and allow all the vlans you want on that trunk.

Then as you say, on switch B for example if you had 3 ports with switches at the other end and you wanted these ports to be in vlan 10,11 and 12 respectively simply configure the ports to be switchports in the correct vlan ie.

int gi0/1

switchport mode access

switchport access vlan 10

int gi0/2

switchport mode access

switchport access vlan 11

int gi0/12

switchport mode access

switchport access vlan 12

then on each switch at the other end simply configure all ports (including the port connected to switch B) to be in the same vlan.

As for a device in vlan 10 for example being able to communicate with any other vlan you will need to do inter-vlan routing somewhere within your network. Without inter-vlan routing then with the above setup devices with a particular vlan will only be able to communicate with other devices in the same vlan.

Jon

Switch A fas0/0------trunk ------ fas0/0 Switch B ---------computer A

                                                                   |----------Computer B

Vlans X, Y and Z

in both switches

fas0/0

sw trun en dot

sw mo trunk

sw trunk allo vlan X Y Z

802.1Q has the concept of Native VLAN, untagged traffic received in any port will be assumed to be part of it. Once the traffic reaches Switch B, the tag will be removed and the it will be forwarded through the interfaces that belong to specific vlans

View solution in original post

Thank you very much fzamora,
I believe you deciphered what I was trying to ask =]

Subnet1.Switch1.vlan1-----trunk.dot1q.nativeVlan100-------|
Subnet2.Switch2.vlan1-----trunk.dot1q.nativeVlan101----SwitchA===trunk.All.sfp===SwitchB===.......
Subnet3.Switch3.vlan1-----trunk.dot1q.nativeVlan102-------|

                                                               |------------trunk.dot1q.nativeVlan100-------Subnet1.Switch4.vlan1

.......=trunk.All.gigabitethernet===SwitchC-----trunk.dot1q.nativeVlan101------Subnet2.Switch5.vlan1

                                                               |------------trunk.dot1q.nativeVlan102-------Subnet3.Switch6.vlan1

great