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Adding stacked 3750's to network

I have a LAN that has 2  3560's  48TS ,  1 on each end of the building,  connected via twisted pair SPF ports.   I'm currently using all 4 channels.

I have just one Vlan.  

I have some spare 3750's   48TS ,    and I just stacked 2 of them and wish to add this stack to the LAN.  

I pulled out one of the SPF modules from a 3560 and inserted it into the master on the stack and connected via crossconnect twistedpair to a 3560.

My spf etherchannels soon go disabled after doing this,  and my only recourse is to reboot the 3560. 

I've opened a TAC case with CISCO but like any tac case I open,  I'm assigned an engineer who's accent is so thick,  I can't understand half of what he's trying to say to me.   Also,  they seem only to be able to help you during my business's working hours where I cannot hook up the 3750's lest I bring down the network. 

I am at a loss,   I have come in early to work,  these last 3 days, before the users get in, trying this and that,  but the bottom line is that I cannot get the 3750's to coincide with the 3560's.

Again,  everything is on 1 VLAN,    ip addresses are good,  gateway, mask addresses are good.   

Hall of Fame Mentor

Re: Adding stacked 3750's to network

Do you get an error on the errdisable?

You don't need to reboot to recover an errdisable state, if you are in the switch CLI, just do a shutdown followed by a no shutdown under the errdisabled interface.

One thing to keep in mind, when configuring etherchannels the source and destination must be the same logical device. Since, you have a 3750 stack, the source can be any of the members of the stack but the destination (your 3560) has to be the same.




Re: Adding stacked 3750's to network

Please clarify.   I don't understand what you mean by "same logical device".

I also don't understand your picture. 

I have switch 3560G-48ts-1.   It is connected to switch 3560G-48ts-2 via a sfp twisted pair module on each switch.    ( I have since disconnected and pulled out the other 3 sfp's I had connecting these switches.)      This all operates on Vlan 1.   The Cisco router is connected to 3560-1. 

Now I am trying to add 2 stacked 3750-48ts's to 3560-1.    I inserted one sfp module into the master 3750 and connect it to 3560-1.   So now 3560-1 has 2 sfp modules in it.

With a pc attached to a port on the 3750's,  I cannot ping the 3560, nor the router,  nor can I login to my domain, etc. etc. 

Shortly later,   all sfp channels go down due to error.   It doesn't state what the error is,  and my only recourse to get everything to work again is to reboot 3560-1 and unplug my connection to the 3750's.

I hope this clears the picture a bit.   I do know that the 3750's have an IP Services image and the 3560's have an IP Base image.   Not sure that matters though.

Hall of Fame Mentor

Re: Adding stacked 3750's to network

On your first post, you mentioned etherchannel then on your recent post, I see no mentioning of etherchannel in your topology.

My diagram was intented to illustrate etherchannel topologies while having a 3750 in your network.

When you stack a pair of 3750 switches, 2 devices become one logical device so in essence, the switch is seen as one device instead of two.

Without knowing the error, it's very hard to help you. I also have a hard time understating your topology and what you have currently configured inside the switches.

If you want further help, I need to see the show running-config from all switches along with a network diagram. Else, you may have to go back to TAC and ask for another engineer that can work with you.




Re: Adding stacked 3750's to network

I assume that the connection between 2 switches,  utilizing the sfp modules,  is an etherchannel? 

Please forgive me,  I am not a certified Cisco network engineer so I am not well versed in the lingo here.

One more time:

switch 1 (3560) connects to switch 2 (3560) via twisted pair sfp module. 

I now wish to add switch 3 (2 stacked 3750's) to the network.

I am doing this by connecting switch 3 to switch 1 via twisted pair sfp module as well.

When I do, all sfp modules (etherchannels),  whatever you want to call them,  go down due to error.

My question is why?

Hall of Fame Mentor

Re: Adding stacked 3750's to network

Please refer to this article so you can understand what Etherchannel is:

I can't help you without seeing errors and switch configuration.


Re: Adding stacked 3750's to network


you should log on  to the console of switch 1 and activate "logging buffer" then connect the 3750 and a minute later do a "show log".

If the ports gets errdisabled the reason should show up here i think.

If there is nothing in the log, do "show interface status" and check the status of the SFP port.

If reaction is slow on the console do "sho proc cpu hist".

Configurations would of course help.


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