Problem with Etherchannel

Unanswered Question
Dec 10th, 2008

Hi all

We have connected 2 building with four 3Com WL-575 Wireless bridge,each two are connected on Cisco3560 switches trunk ports, and these trunk ports are configured as Etherchannel,

The problem is when the Remote Desktop is accessed from any site,the Port channel goes down and not able to access the Remote Desktop.

Please help


I have this problem too.
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SJessulat_2 Wed, 12/10/2008 - 22:30


just to check: You connected four wireless bridges (each with one port) to one C3560 Switch. And on that switch You configured these four ports into one EtherChannel?

If i got that right, then this is a slight misunderstanding of an EtherChannel. An EtherChannel bundles multiple uplinks between TWO devices to combine their bandwidth.

So all of the ports of one EtherChannel have to start on one device and end on another single device.



sudeesh12 Wed, 12/10/2008 - 22:42


Thanks for ur reply,

Two Bridges are connected on one Switch in one site and the other two bridges connected on other switch .two ports of each switch is bundled as etherchannel, this etherchannel is started on one switch and ended on other switch

I hope now u got the scenario


SJessulat_2 Wed, 12/10/2008 - 22:44

Ahh, ok, now i get it.

Hmm, maybe it's a problem with vlans.

What is the message appearing when the EtherChannel goes down?

sudeesh12 Wed, 12/10/2008 - 22:59

The message is Port-channel 1 is down,

We can ping all device from one site to other as well .

SJessulat_2 Wed, 12/10/2008 - 23:04

Could You paste the config (or part of it) of one or both switches. This would help, i think.

sudeesh12 Wed, 12/10/2008 - 23:40

This is the config on both Switches

inteface port-channel 1

switchport trunk encapsulation isl

switchport mode trunk




interface FastEthernet0/45

switchport trunk encapsulation isl

switchport mode trunk

channel-group 1 mode desirable


interface FastEthernet0/46

switchport trunk encapsulation isl

switchport mode trunk

channel-group 1 mode desirable

rgodden Thu, 12/11/2008 - 03:20

Can the 3com devide handle cisco proprietry ISL frames ?

felipe.santarelli Thu, 12/11/2008 - 04:26

The ISL is incapsulated, there should be no problem for the bridges to handle it.

My guess is something with the MTU. Have you checked both on Cisco and 3Com for them to accept all sizes, like enabling jumboframe?

Also, try to change the encapsulation to dot1q which is interoperable between multi-vendor products.

sudeesh12 Sat, 12/13/2008 - 00:04


I didnt checked for MTU and Jumbo frames

I tried dot1q,With dot1q also not working



MARK CHRISTY Tue, 11/19/2013 - 14:48

With the same exact topology, I was having a similar problem because I had a transparent unmanaged switch between my cisco port, and the wireless equipment (cable length > 327 feet or 100 m). The unmanaged switch could not pass maximum size valid ethernet frames when TAGGED or using vlan trunks. It adds 4 bytes to the frame making a 1522 byte frame. Most TCP applicaitons try to use the maximum MTU ethernet frame, so when they do, the tag + 4 bytes makes those packets dissappear. Removing those devices fixed my problem.


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