Network Interview Question Today

[Vegito]

One question I got was

What can cause a switch port to disable itself, what can you check to fix the problem

I wasn't sure because in 5 year of dealing with cisco product, not one switched port died..

I put it could be duplexing or speed sensing problem.. I google and saw similar answer but what else can it be ? If its not physical cabling problem...

 

[spidey07]

whole lot of reasons...

port security
increasing errors (this is really common and probably what they were looking for to see if you had any experience...most likely cause is speed/duple mismatch or cable problem)
uni-directional link detection (detects a one-way link and disables the port...a god send)
bdpuguard (if a spanning-tree bdpu is seen on the port, shut it down)


Here's a shot of error disable/recovery on a 6500...so a port can be shutdown for any of the reasons listed. You can also control what and how the errdisable happens.

ErrDisable Reason Detection status
----------------- ----------------
udld Enabled
bpduguard Enabled
security-violatio Enabled
channel-misconfig Enabled
psecure-violation Enabled
unicast-flood Enabled
pagp-flap Enabled
dtp-flap Enabled
link-flap Enabled
l2ptguard Enabled
gbic-invalid Enabled
dhcp-rate-limit Enabled
unicast-flood Enabled
arp-inspection Enabled
inline-power Enabled
packet-buffer Enabled

 

[Vegito]

wow.. that is a lot.. at least that was my answer, duplex/speed.. got lucky with that one.. dodge a bullet.. thanks spidey

 

[spidey07]

just thought I'd open the hose and let you drink.

search cisco.com on "error recovery" or "errdisable" for more.