Vlan trunk problem

Question

Hi,
Im configuring a vlan trunk between 2 switches but I'm having a problem somehow.
Switch 1 a Cisco 3750G n
name: alrswcc00
interface GigabitEthernet1/0/28
 description Uplink Alrswcc20
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 1-30
 switchport mode trunk
end
Name: Gi1/0/28
Switchport: Enabled
Administrative Mode: trunk
Operational Mode: trunk
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
Voice VLAN: none
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk private VLANs: none
Operational private-vlan: none
Trunking VLANs Enabled: 1-30
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL
Switch 2 a Cisco 2960S
name: alrswcc20
interface GigabitEthernet1/0/25
 description Uplink Alrswcc00
 switchport trunk allowed vlan 1-30
 switchport mode trunk
end
Name: Gi1/0/24
Switchport: Enabled
Administrative Mode: trunk
Operational Mode: trunk
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 10 (Inactive)
Administrative Native VLAN tagging: enabled
Voice VLAN: none
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk associations: none
Administrative private-vlan trunk mappings: none
Operational private-vlan: none
Trunking VLANs Enabled: 10,20,30,40
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Then lastly on switch 2 I created a port for an Ubiquiti access point with following settings.
interface GigabitEthernet1/0/24
 switchport trunk native vlan 10
 switchport trunk allowed vlan 10,20,30,40
 switchport mode trunk
end
But my AP doesn't seem the get an IP. Where as if I plug it in on Switch 1 it does with the same settings.
So I am assuming there is something wrong with my trunk. What am I doing wrong?
Thank you,
Michael

Answer 1

Here are a couple of observations:
1.  The switchport trunk encap dot1q command was not applied on the 2960 because 802.1q trunking is the default.  The 2960 series switches do not support ISL encapsulation, as the OP observed.  There is, therefore, no need to manually specify the trunking protocol.  The show int g1/0/24 switchport command confirmed that trunking is working.  I find the show int g1/0/24 trunk command to be more informative in this context.  It tells you what VLANs are active and trunking between the connection.
2.  You do need to define VLANS 2-30 on your second switch. You can do so manually or you can configure VLAN Trunking Protocol (VTP).  VTP is your easiest bet.  Example config:
Switch 1
sw1(config)# vtp mode server
sw1(config)# vtp version 2
sw1(config)# vtp domain MY_DOMAIN
sw1(config)# vtp password MySecret
Issue a show vtp status  in priv exce mode to very your settings.
Switch 2
sw2# show vtp status
Do this command FIRST and make sure that the configuration revision number is smaller than the revision number of SW1.
VTP Operating Mode                : Client
Maximum VLANs supported locally   : 255
Number of existing VLANs          : 25
Configuration Revision            : 174
If config revision on SW2 is greater than config revision of SW1, then issue following command:
SW2(config)# vtp domain bogus
SW2(config)# vtp domain MY_Domain
SW2(config)# do show vtp status
Your config revision should go back to zero.
Now issue the same commands on SW2. 
SW2(config)# vtp version 2  (pretty sure that is default, but I issue it anyway)
SW2(config)# vtp mode client (means you cannot define VLANs on this switch.  Most admins prefer that only one switch be capable of creating VLANs).
SW2(config)# do sh vtp status
The config revision was important because injecting a switch into your network that has a higher VTP revision can overwrite your existing VLAN database.  If that happens, chances are that most of your network traffic will cease to function as all of your access ports will be in a VLAN mismatch mode.