Problems to add a VLAN to a working Cisco to IBM(AIX) Etherchannel

[vftgcosta]

Hi,

We have 4 Etherchannels between a stack of five 3750E-48TD and four IBM AIX.

The IBM AIX are configured as Etherchannel and the stack is also configured as etherchannel (here's an exemple of one of the POs):

interface Port-channel16
description ADPAIX03
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1284,1285,1316,1794-1799,1814,1828,1833,1839
switchport mode trunk

interface GigabitEthernet1/0/23
description ADPAIX03
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1284,1285,1316,1794-1799,1814,1828,1833,1839
switchport mode trunk
channel-group 16 mode on

interface GigabitEthernet3/0/20
description ADPAIX03
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1284,1285,1316,1794-1799,1814,1828,1833,1839
switchport mode trunk
channel-group 16 mode on

SW01#sh run int vlan 1839

ip address 192.168.2.1 255.255.255.0

The problem was that when we added a new vlan, we could see the mac address of the AIX on the switches ARP table but were unable to ping the AIX. Only after we issued a shut/no shut to the PO we could then ping the AIX sucessfully.

Has anyone encountered a similar issue? Should we use LACP instead of etherchannel?

Thanks in advance

[Michael Odom]

Switching to LACP shouldn't make any difference.  LACP just handles the etherchanneling, not the 802.1q trunking, and it sounds like your problem is specific to trunking.  It could be that resetting the links reset something on the AIX server that caused it to start working.  You might also have had something wierd happening with spanning-tree on that VLAN.  If you can recrate the issue, or are having the issue with another host, you might take a look at the output of show spanning-tree int po 16 and show spanning-tree vlan , and see if everything is how you expect it to be.