Hosts flapping on switches after etherchannel set up

[18121999]

Hi guys,

I am having a problem with the dual cisco 4506 switches placed at the core of our network. Both switches are connected via the 2 gigabit ports on each switch - gi1/1 &gi1/2 on each server.
Now my problem is I tried to create an ether channel to bundle the links, this is the command I used on each switch:

Interface range gi1/1 - 2
Channel-group 1 mode on
Switchport trunk encapsulation dot1q
Switchport mode trunk

Interface Port-channel 1
Switchport
Switchport trunk encapsulation dot1q
Switchport mode trunk

As soon as I put the command in, there were a series of errors in the logs on both switches for so long. I gave it over 40 minutes for STP to fully negotiate but it obviously didn't happen. I had to eventually shut down one gigabit interface on one of the switches while I further investigated as network traffic slowed down considerably and users had started coming in.
What am I doing wrong??
Any help will be appreciated

Error log:
May 19 07:41:35.769: %C4K_EBM-4-HOSTFLAPPING: Host 00:02:55:47:17:63 in vlan 1 i
s flapping between port Po1 and port Gi1/2
May 19 07:41:38.077: %C4K_EBM-4-HOSTFLAPPING: Host 00:02:B32D:80 in vlan 1 i
s flapping between port Gi1/2 and port Po1
May 19 07:41:53.713: %C4K_EBM-4-HOSTFLAPPING: Host 00:09:6B:B1:47:8A in vlan 1 i
s flapping between port Gi1/2 and port Po1
May 19 07:42:00.181: %C4K_EBM-4-HOSTFLAPPING: Host 00:04C:0D:8B:2E in vlan 1 i
s flapping between port Gi1/2 and port Po1
May 19 07:42:03.137: %C4K_EBM-4-HOSTFLAPPING: Host 00:02:B32F:53 in vlan 1 i
s flapping between port Po1 and port Gi1/2

Relevant portion of config:

interface Port-channel1
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
!
interface GigabitEthernet1/1
switchport trunk encapsulation dot1q
switchport mode trunk
channel-group 1 mode on
!
interface GigabitEthernet1/2
switchport trunk encapsulation dot1q
switchport mode trunk
channel-group 1 mode on

Thanks.

 

[ccmuser]

try this command it will tell you what port have joined Channel

show etherchannel 1 port-channel

There error means the switch is passing traffic over an interface in the bundle and over the regular gige port not in the bundle.. this is and stp violation..In essence it is telling you there is a possible loop forming..

Try desirable instead of on..

and verify all interfaces are configed the same and have machting trunk configs on all four interfaces ( very important)

 

[18121999]

Thanks ccmuser for the prompt response.
I will try this again and let you know how I get on.