Confusing Situation at Work Today, Need Some Guidance

Danielh22185 · July 2012

This may seem as common grounds for many of you here but I ran into this issue today at work. An onsite tech called into the NOC stating that he was seeing an amber light on a L3 switch. He immediately thought the connecting port of the amber light was indicating err-disabled. So naturally I got the loopback IP from him and proceeded to troubleshoot by logging into the switch.

The tech claimed the port went amber on port 7/3, a gig port. I proceeded to do a 'show interface status err-disabled'. I couldn't even use this command on the L3 switch. This was on an older switch running IOS 12.1 so that may have been the cause for that. Next, I thought okay well let me look up the port, typed in: 'sh int gi7/3', nothing. So then I proceeded with a: 'sh ip int bri' I could now see interfaces BUT they were all VLANs and a few loopbacks. Now I’m beginning to get lost. I basically am not seeing a whole lot of anything the onsite tech is seeing physically.

I asked if this port was a part of any VLAN on the switch. He believed it was a member of a vlan, vlan46. So I did a 'show int vlan46' and got some information about the vlan. What interested me here was the hardware description. It stated the following:
Hardware is Cat6k RP Virtual Ethernet, address xxxx.xxxx.xxxx
Description: from 5/14 to: (a "connecting L2 switch name xxxx")

Now you can image my confusion level rising. I still am trying to wrap my head around why the tech is seeing an amber light on the L3 device, he sees a port, but I cannot see anything physically from show commands on the switch.

As it turns out from a level 2 engineer from my NOC took over on the situation. At this point there was a shutdown port on the connecting L2 switch that connects to the L3. I guess my biggest confusion is how the L2 switch is connecting to the L3 switch if I cannot see any physical ports listed on the L3 switch. Also, how was this showing an amber port on the L3 switch?

Sorry for the novel but this really bugged me today. I am still pretty new to working professionally in the networking world but this seemed like something rather fundamental I was just totally missing.

Ideas or suggestions on what I might have missed / could have checked? Let me know if this wasn't enough information. I have tried to explain as much as I could about the situation w/o leaking corporate information about the network. Thanks!

NetworkVeteran · July 2012

Danielh22185 wrote: »

He immediately thought the connecting port of the amber light was indicating err-disabled. So naturally I got the loopback IP from him and proceeded to troubleshoot by logging into the switch.
The tech claimed the port went amber on port 7/3, a gig port. I proceeded to do a 'show interface status err-disabled'. I couldn't even use this command on the L3 switch. This was on an older switch running IOS 12.1 so that may have been the cause for that. Next, I thought okay well let me look up the port, typed in: 'sh int gi7/3'.. nothing. So then I proceeded with a: 'sh ip int bri' I could now see interfaces BUT they were all VLANs and a few loopbacks. Now I’m beginning to get lost. I basically am not seeing a whole lot of anything the onsite tech is seeing physically. I asked if this port was a part of any VLAN on the switch.

Begin with "show run int Gig7/3" That should tell you quite a bit--specifically, whether it's a L2 switchport or a L3 interface, and any interesting confguration. I often do "show run | inc 7/3" as well to look for related subinterfaces to avoid any surprises.

Hardware is Cat6k RP Virtual Ethernet, address xxxx.xxxx.xxxx
Description: from 5/14 to: (a "connecting L2 switch name xxxx")

They may have given you the wrong VLANID or the description could be stale. "show int Gig7/3 switchport" is likely the command you wanted.

I guess my biggest confusion is how the L2 switch is connecting to the L3 switch if I cannot see any physical ports listed on the L3 switch.

An L3 switch can have L2 ports, in which case "show interface" isn't so illuminating.

I am still pretty new to working professionally in the networking world but this seemed like something rather fundamental I was just totally missing.

Start studying for the CCNP Switch exam.

Danielh22185 · July 2012

Ya I realize some of this is over my head at the moment because I only have a CCNA background. I am studying Route currently so Switch will come soon after.

What I thought was odd was the sh interface commands simply were not working. I also don't understand why I would see zero physical ports on the L3 device and only logical stuff.

NetworkVeteran · July 2012

Danielh22185 wrote: »

What I thought was odd was the sh interface commands simply were not working. I also don't understand why I would see zero physical ports on the L3 device and only logical stuff.

I'd also be skeptical of things said but not seen. For example, his estimation of which switch an interface has an amber LED. I sometimes do something to prove it, like a quick shut / no shut of the interface if that won't have any terrible repercussions (verify first!).

(Of course, do this in a nice way, not an accusatory tone!)

kmcintosh78 · August 2012

Yeah, some of the IOS and older devices will not support the generic "sh int" command.
Learn the Pipe command, it is SO valuable.
There are some devices, like the ASAs that the port goes Amber when it establishes a Gig connection.
Try some of these commands as well.
show int status
show int status | inc connected
show int counters errors

Poke around with the ? command.

I work solely in a L2 environment, minus the ASA, so I deal with switches all day.

Confusing Situation at Work Today, Need Some Guidance

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