trunk port issue

[shrinivas.k]

Hi,

We are try to connect some AP's to trunk port on switch 3750 & AP's are not coming up with IP address from DHCP server ....if suppose we will configure the interface as normal access port, AP"s are getting IP & working also.....We have cross checked port configuration & it is correct....Please let me know whether the vlan dot1q tag native command is creating the problem....this is enabled in the switch.

my port configurations as below.

interface FastEthernet1/0/4

switchport trunk encapsulation dot1q

switchport trunk native vlan 2

switchport trunk allowed vlan 2,10

switchport mode trunk

no logging event link-status

spanning-tree portfast

end

RACKA-SW1#sh int fa1/0/4 trunk

Port        Mode             Encapsulation  Status        Native vlan

Fa1/0/4     on               802.1q         trunking      2

Port        Vlans allowed on trunk

Fa1/0/4     2,10

Port        Vlans allowed and active in management domain

Fa1/0/4     2,10

Port        Vlans in spanning tree forwarding state and not pruned

Fa1/0/4     2,10

RACKA-SW1#sh int fa1/0/4 switchport

Name: Fa1/0/4

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: 2 (V-CH)

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: 2,10

Pruning VLANs Enabled: 2-1001

Capture Mode Disabled

Capture VLANs Allowed: ALL

[ranraju]

Hi Shrinivas,

On the access ports the frames that switch receives are untagged. If you explicitly configure that access port to be in a vlan x then that frame would be belong to vlan x. By default the port will be in vlan 1 then all the frames that are coming into the switch through that port would belong to vlan1.

So, if the link connected to the AP is made an access port with default port configuration (port would be in vlan 1) - and the AP gets an IP address from the DHCP it indicates that the DHCP server is in VLAN1 or its able to reach the DHCP server through VLAN1. ------ if this is working then you need to allow vlan 1 on the trunk and configure vlan 1 as native vlan, with this the AP would get an IP address.

else...

I am not sure if you'd configured the access-port to be in vlan 2 so that it gets an IP from the DHCP server - if this is true then yes "vlan dot1q tag native" could be causing the issue, the configurations on the AP has to be checked. You can confirm this by removing this configuration on the trunk and see if the AP can get the IP address from the DHCP server.

Hope this answers your question.

Regards,

Ranraju