# Trunk Port(Tag Port)

## 1-1 What's Trunk port?

 A trunk port is a port that is assigned to carry traffic for all the VLANs.Trunk send Untagged and Tagged information. There are two standards for Trunking:

* ISL(Cisco)
* 802.1Q(Industry Standard) is 4 Byte which is considered without Native Vlan

**Example:**

![Trunk between two switches](/files/-LAPD517Yheb1Bx_qoVt)

```
sw1(config)# int fa0/1
sw1(config-if)# switchport mode trunk
```

```
sw2(config)# int fa0/1
sw2(config-vlan)# switchport mode trunk
```

{% hint style="info" %}
In older version of Cisco devices first you have to write:

 *switchport encapsulation dot1q* 

then  

*switchport mode trunk*
{% endhint %}

## 1-2 Changing Native Vlan

For changing Native Vlan just write:

```
sw1(config)# int fa0/1
sw1(config-if)# switchport trunk native vlan 20
```

## 1-3 Allow Specific Vlan

To allow specific vlan just write:

```
sw1(config)# int fa0/1
sw1(config-if)# switchport allowed vlan 10,20,30
```

In above-mentioned code, just vlan 10, 20, 30 allowed through trunk port

{% hint style="info" %}
You can use switchport command with add/all/except/none 

```
sw1(config-if)# switchport allowed vlan 10,20,30
sw1(config-if)# switchport allowed vlan add/all/except/none 10,20,30
```

{% endhint %}

## 1-4 How to see trunk port

```
switch# show interface trunk
or 
switch# show interface fa0/1 switchport
```


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