Etherchannel Summary

[Sharin Taib]

I have a etherchannel setup but it seems that the port-channel is down while the ports are up.

6509E#sh etherchan sum

Group  Port-channel  Protocol    Ports

------+-------------+-----------+-----------------------------------------------
3      Po3(SD)         PAgP      Gi2/1(I)       Gi2/5(I)       Gi2/6(I)
                                 Gi3/12(I)

C6509E#sh int po3
Port-channel3 is down, line protocol is down (notconnect)

the 4 ports are configured as such

 switchport
 switchport access vlan 10
 switchport mode access
 logging event link-status
 spanning-tree portfast edge
 channel-group 3 mode desirable

I tried to reset the port-channel 3 but it refuses to be up.

Any advice?

[RafaelSpain]

Hi Sharin,

Has you configurated the Ethernet-Channel on the other end of the link (the other switch on the link)?

[Sharin Taib]

the other end is a windows server that is doing "teaming", so I believe yes.

[Peter Paluch]

Hi Sharin,

You have configured your EtherChannel to use the PAgP negotiation protocol (this follows from the mode desirable). However, PAgP is Cisco proprietary, and most certainly, Windows do not support it. As a result, the creation of the EtherChannel is not negotiated successfully, and the Port-channel interface never goes up.

You will need to check whether your Windows server and NIC drivers support LACP to negotiate the "teaming". If so, you will need to remove the Port-channel configuration from your switch and recreate it anew using channel-group 3 mode active that activates LACP. If there is no LACP support on your Windows server then you will need to use the channel-group 3 mode on that runs EtherChannels statically without resorting to any negotiation.

Please be aware that when you remove the channel-group or the entire Port-channel interface, the physical interface may be automatically shut down, and you will need to activate it again.

Best regards,
Peter

[Sharin Taib]

ok. will no int po3 and then modify the ports to be channel-group 3 mode on

will try it again soon

[paul driver]

Hello

Configure one side of this etherchannel
channel-group 1 mode auto

res

Paul

[Peter Paluch]

Hi Paul,

Configure one side of this etherchannel
channel-group 1 mode auto

I am sorry but this won't solve the problem. mode auto is PAgP again, just in passive mode (expecting the other side to start PAgP negotiation). Windows will never start or respond to PAgP because they do not support it - they never have.

The desirable and auto modes imply PAgP.  The active and passive modes imply LACP. The on mode does not start any negotiation protocol.

Best regards,
Peter

[paul driver]

Hello

No need to be sorry peter -Although I think I understand etherchannel my TS process is obviously different than yours.

I have indeed found on occasions with LACP/PAgP paring a port-channel to active/passive or auto/desirable does sometime fix an issue pertaining negotiation than having the same mode configured either side of the link.

My next step would have been requesting Sharin to turn off negotiation and test

res
Paul

[Sharin Taib]

ok something happened.

i issued this onto all 4 interfaces

no channel-group 3 mode desi

channel-group 3 mode on

and the port channel came up BUT the server became unpingable.

So I had to go back to the previous config

and this time the port channel went down BUT the server became pingable.

so now I'm left confused.

[Peter Paluch]

Hi Sharin,

I think that you are experiencing an inconsistency in how the individual ports are handled by the switch. You have to keep in mind that if ports grouped under a dynamic (LACP or PAgP-based) EtherChannel are not successfully negotiated as bundled ports, they will still be kept as individual ports (marked with I in the show etherchannel summary output). Some switches continue using individual ports as normal ports - as if the EtherChannel was not even configured. Some others will consider them unusable and unsuitable to carry traffic. This may differ based on the actual mode and certainly on the switch platform. Some switches even allow you to configure how the ports are to be treated if they remain as individual ports.

Quite frankly, I do not believe that it is in any way useful to experiment with PAgP dynamic modes toward a Windows server. As I cautioned, Windows do not speak PAgP and so all attempts at running it toward a Windows host are futile. Either test LACP (mode active) or static EtherChannel (mode on).

Best regards,
Peter

[Sharin Taib]

sorry. made a typo. edited the earlier comment

i changed from desirable to on. my port-channel interface went up/up

the FE ports all came up and were marked with a P under etherchan sum output.

but my server was unpingable for awhile.

seeing that, i set it back to desirable again and the server was pingable. bu etherchan sum was marked with an I

[Peter Paluch]

Sharin,

I am afraid we're going round in circles. Attempting to solve this problem by randomly testing different EtherChannel modes is not going to provide satisfactory results. I believe you need to very carefully inspect the configuration of the Windows server and the way the teaming is configured there before making a conclusion whether the EtherChannel mode to be used is LACP-based (mode active/mode passive) or static (mode on), or whether the teaming as configured is actually compatible with EtherChannel at all. Definitely, though, PAgP (mode desirable/mode auto) is out of the question. Windows don't speak PAgP, period. It can't be made more plain than that. It appears to work only because it leaves the ports still operating as individual ports, as the negotiation has failed.

Best regards,
Peter

[Sharin Taib]

Oh. I don't think we are going in circles. I was merely trying to figure out if i set it to mode on, would the etherchannel work. as it didn't, i have forwarded it to the owner of the server to check on their end as leaving as mode on is the best way to troubleshoot. that's all. not throwing random commands hoping the problem will go away. this is a legacy configuration which I'm trying to clean up.

[Peter Paluch]

Hey Paul,

Although I think I understand etherchannel my TS process is obviously different than yours.

That's the great thing about these forums ;) To your former suggestion, I did not really object to using the auto / desirable combination even though the best practice is to use both ends as desirable. Rather, I wanted to point out that in my previous response, I explicitly stated that Windows have never spoken PAgP so it is a futile attempt to configure an EtherChannel toward a Windows server to be PAgP-negotiated, while your suggestion was again in favor of running PAgP which didn't really make sense to me.

In my opinion, Sharin needs to stop randomly throwing different EtherChannel modes at the Windows server (I never saw him configure LACP, though, which I recommended doing in the first place), and instead make himself perfectly acquainted with the way the teaming is configured on Windows, and only then make an informed choice of the proper method. Without knowing how the teaming is configured, what it expects from the switch and whether these requirements can be met at all, this whole exercise may be useless.

Best regards,
Peter