1.3 VLAN Trunks

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1.3 VLAN Trunks

Last updated: November 26, 2014

Load the CCNP-Switch-Task1-3 initial configurations before starting.

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Tasks

  • Configure all inter-switch links shown in the topology diagram above as 802.1q VLAN Trunks using the following criteria:
    • 802.1q Trunks should be negotiated between switches using some combination of DTP modes.
    • If an 802.1q Trunk stops receiving DTP keepalives from its peer switch, that Trunk should fallback to an Access Port in VLAN-2.
    • The Native VLAN of all 802.1q Trunks should be set to VLAN-3.

All preconfigured Enable passwords are ine

Switch-1 Configuration

Switch-1#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
Switch-1(config)#interface range fastethernet 0/10 - 15
Switch-1(config-if-range)#switchport trunk encapsulation dot1q
Switch-1(config-if-range)#switchport mode dynamic desirable
Switch-1(config-if-range)#switchport access vlan 2
Switch-1(config-if-range)#switchport trunk native vlan 3
Switch-1(config-if-range)#no shutdown
Switch-1(config-if-range)#end
Switch-1#

Repeat the same steps above on Switch-2 and Switch-3, substituting the appropriate interface numbers.

Verification

Many switches that support both ISL and 802.1q Trunking methods will first require you to select one or the other before configuring the switchport mode command. That's why this example started with the switchport trunk encapsulation dot1q command.

The first two criteria required you to use some form of the switchport mode dynamic command. In the example, all of the switchports have been configured as dynamic desirable, but you could also have selected dynamic auto on one side of any given link (as long as the other side of that same link was desirable).

The command switchport access vlan 2 ensured that if this interface ever fell back to being an Access Switchport, it would be in Access VLAN-2. Finally, you needed to use the switchport trunk native vlan command to ensure that the Native VLAN was set to VLAN-3.

To verify that your interfaces were operational as 802.1q VLAN Trunks (and utilizing VLAN-3 as the Native VLAN), there are several commands you could have issued. Shown below is the output of the command show interface trunk.

Switch-1 Verification

Switch-1#show interface trunk

Port        Mode             Encapsulation  Status        Native vlan
Fa0/10      desirable        802.1q         trunking      3
Fa0/11      desirable        802.1q         trunking      3
Fa0/12      desirable        802.1q         trunking      3
Fa0/13      desirable        802.1q         trunking      3
Fa0/14      desirable        802.1q         trunking      3
Fa0/15      desirable        802.1q         trunking      3

<output omitted for brevity>

The command show interface switchport | include (Name|Access) could be used to verify that if any trunk fell back to being an Access Switchport, it would be in Access VLAN-2.

Switch-1#sho interface switchport | include (Name|Access)  
Name: Fa0/1
Access Mode VLAN: 1 (default)
Name: Fa0/2
Access Mode VLAN: 1 (default)
Name: Fa0/3
Access Mode VLAN: 1 (default)
Name: Fa0/4
Access Mode VLAN: 1 (default)
Name: Fa0/5
Access Mode VLAN: 1 (default)
Name: Fa0/6
Access Mode VLAN: 1 (default)
Name: Fa0/7
Access Mode VLAN: 1 (default)
Name: Fa0/8
Access Mode VLAN: 1 (default)
Name: Fa0/9
Access Mode VLAN: 1 (default)
Name: Fa0/10
Access Mode VLAN: 2 (VLAN0002)
Name: Fa0/11
Access Mode VLAN: 2 (VLAN0002)
Name: Fa0/12
Access Mode VLAN: 2 (VLAN0002)
Name: Fa0/13
Access Mode VLAN: 2 (VLAN0002)
Name: Fa0/14
Access Mode VLAN: 2 (VLAN0002)
Name: Fa0/15
Access Mode VLAN: 2 (VLAN0002)
Name: Fa0/16
Access Mode VLAN: 1 (default)
Name: Fa0/17
Access Mode VLAN: 1 (default)
Name: Fa0/18
Access Mode VLAN: 1 (default)
Name: Fa0/19
Access Mode VLAN: 1 (default)
Name: Fa0/20
Access Mode VLAN: 1 (default)
Name: Fa0/21
Access Mode VLAN: 1 (default)
Name: Fa0/22
Access Mode VLAN: 1 (default)
Name: Fa0/23
Access Mode VLAN: 1 (default)
Name: Fa0/24
Access Mode VLAN: 1 (default)
Name: Gi0/1
Access Mode VLAN: 1 (default)
Name: Gi0/2
Access Mode VLAN: 1 (default)
Switch-1#
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