Layer 2 "down/down" on Port channel after issuing "speed 100" command on 3750E switches

[Eric McMiller]

Hello all!

First discussion post here...

I have two 3750E switches in my home lab with gigE (1000mbps) ports.  The ports on switch1 are connected to to ports on switch2 with gigE cables.  

When I create the Port channel, it works fine and the layer 2 status is "up/up" (on both sides).  However, when I issue the "speed 100" command, the Port channel (and all corresponding ports bundled within the Port channel) immediately transition to "down/down".  The reason I would strongly prefer the links to act as FastEthernet ports is to match the INE lab workbook I purchased.  Everything in the Switch lab is all FastE including show commands, screenshots, etc..

I don't have my home lab's screenshots with me right now.  I'd be happy to share more later today, but the best I can do right now is offer this general description.  I feel like I've exhausted all the troubleshooting techniques I can think of...  I've flapped the individual links.  I've flapped the Port channels.  I've swapped cables.  I've tried entering the commands in different ways (in case this was related to an order of operations).

Does the 3750E switch even support the "speed 100" command on Port channels?  It lets me enter the command, but I have not had any luck getting it to work.

[paul driver]

Hello

The port-channel need to be consistent both ends to the link- and on the physical interfaces its bound to,

So if you have a speed mix-match then the ehterchannel with be torn down.

So when creating a L2 PC from scratch, I would suggest shutting your physical interface down and then apply the correct speed/duplex etc, then assign it to a channel-group and then let the logical interface of the PC to be created automatically.

Apply the trunking etc,, there after to the PC NOT the physical interfaces

Lastly enable the physical interfaces.

res
Paul

[Eric McMiller]

I'll try this approach (with screenshots) and reply back.

Thanks Paul!

[Eric McMiller]

Even by following the appropriate order of operations - and I believe you have articulated it perfectly in your post - it still does not work on my side.

Would it be helpful to share my switches iOS version?    Here it is:


Sw1#sh ver
Cisco IOS Software, C3750E Software (C3750E-UNIVERSALK9-M), Version 15.0(2)SE10, RELEASE SOFTWARE (fc2)

[Richard Burts]

Since a port channel is a virtual interface and aggregates some number of physical ports, I am puzzled at the attempt to apply a speed command to the port channel. It might make sense to set the speed of a physical interface but I do not see the purpose on a virtual interface.

Some switch Gig interfaces can be set to run at lower speed and some run only at Gig speed. I am not clear whether the Gig interfaces on your switch support setting the speed to 100. Can you try setting the speed on one of the physical interfaces and let us know the result?

HTH

Rick

[Eric McMiller]

Yes, I can try this and reply back with the result.

It's a unique situation as I am trying to force my switches to act in a legacy fashion to match my INE workbook (and ensure I'm doing things correctly to their specifications, such as proper Spanning-tree root bring election in my home network).  I will certainly let you know.  Thanks Rick!

[Eric McMiller]

Here is another twist which factors in Layer 1.  I have an old "category 5" cable with a maximum speed of 100mbps.  When I plug in this cable, my switches communicate successfully at FastEthernet speed in an "up/up" state.  Again, I believe this lends itself to the theory that my 3750E gig ports do not support the "speed 100" command.  What do you think about this?

[GRANT3779]

Out of interest do the ports come up/up if you manually set speed to 1000Mbps rather than let it auto negotiate?

[Eric McMiller]

Good question.  Interestingly, they do not.  Similar to my previous posts - after adding the "speed 1000" device to the ports - the result is Layer 2 "down/down".  Here is the output of my show commands on both devices:

Sw1#sh ip int bri
.
GigabitEthernet1/0/1 unassigned YES unset up up
GigabitEthernet1/0/2 unassigned YES unset administratively down down
GigabitEthernet1/0/3 unassigned YES unset administratively down down
GigabitEthernet1/0/4 unassigned YES unset administratively down down
GigabitEthernet1/0/5 unassigned YES unset administratively down down
GigabitEthernet1/0/6 unassigned YES unset administratively down down
GigabitEthernet1/0/7 unassigned YES unset administratively down down
GigabitEthernet1/0/8 unassigned YES unset administratively down down
GigabitEthernet1/0/9 unassigned YES unset administratively down down
GigabitEthernet1/0/10 unassigned YES unset down down
GigabitEthernet1/0/11 unassigned YES unset down down
GigabitEthernet1/0/12 unassigned YES unset down down
GigabitEthernet1/0/13 unassigned YES unset down down

========================================================

Sw2#sh ip int bri
.
GigabitEthernet2/0/1 unassigned YES unset down down
GigabitEthernet2/0/2 unassigned YES unset administratively down down
GigabitEthernet2/0/3 unassigned YES unset administratively down down
GigabitEthernet2/0/4 unassigned YES unset up up
GigabitEthernet2/0/5 unassigned YES unset administratively down down
GigabitEthernet2/0/6 unassigned YES unset administratively down down
GigabitEthernet2/0/7 unassigned YES unset administratively down down
GigabitEthernet2/0/8 unassigned YES unset administratively down down
GigabitEthernet2/0/9 unassigned YES unset administratively down down
GigabitEthernet2/0/10 unassigned YES unset down down
GigabitEthernet2/0/11 unassigned YES unset down down
GigabitEthernet2/0/12 unassigned YES unset down down
GigabitEthernet2/0/13 unassigned YES unset administratively down down

.

[Rob Cluett]

Eric, did you set 1000mpbs/full on both sides for your test?

[Eric McMiller]

Yes.  Both sides.  So I configured it as follows...

SW1:

conf t

int ra gi1/0/10-12

speed 1000

end

SW2:

conf t

int ra gi2/0/10-12

speed 1000

end

Results shown above via the "sh ip int bri" command.

[Rob Cluett]

Do you have another switch to test with? in other words eliminate one of the 3750's.

or

I'm not sure this will work but plug an Ethernet into two ports on one 3750 and see if you can get them to run at the 100 speed.

Are the 3750's new... out of the box?

[Eric McMiller]

They are used.  I bought them second-hand, on eBay. I can plug one of my FastEthernet cables and get them to run at 100 speed.  I've verified this works, which is a bit odd to me, but I'm glad to verify this once again.

I do have a 3rd 3750 which I could try testing.  I'm still wondering if this has to do with what you mentioned earlier regarding negotiation, but I'm not certain - its just a thought. I'll try the debugging, as well.

[Rob Cluett]

When you try the debugging set it to all scenarios.

1) "negotiation auto"

2) "speed 1000" and "deplux full"

3) "speed 100" and "deplux full"

From the debug we should see the point at which it fails.

[Eric McMiller]

Are there more commands that I need to execute in order to achieve an output similar to what you captured, above?

For instance, I enabled "terminal monitor", before I executed the "debug ethernet interface" command, but I'm not sure that's enough to display the proper debug messages on-screen.