Flapping circuit question and loopback question...

[uubozou11]

Two questions)

1) If someone reset a pc or cable modem will that cause the circuit to flap (as shown below)?

054396: Oct 21 19:51:24.288 PDT: %LINK-3-UPDOWN: Interface FastEthernet0/25, changed state to down

054397: Oct 21 19:51:25.289 PDT: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/25, changed state to down

054398: Oct 22 04:11:50.740 PDT: %LINK-3-UPDOWN: Interface FastEthernet0/25, changed state to up

054399: Oct 22 04:11:51.776 PDT: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/25, changed state to up

054400: Oct 22 04:12:29.280 PDT: %LINK-3-UPDOWN: Interface FastEthernet0/25, changed state to down

054401: Oct 22 04:12:30.308 PDT: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/25, changed state to down

2) Does this mean someone plugged a loopback adaptor into a switch port?

020561: Oct 20 02:21:12.212 PDT: %LINK-3-UPDOWN: Interface FastEthernet0/12, changed state to up

020562: Oct 20 02:21:14.004 PDT: %ETHCNTR-3-LOOP_BACK_DETECTED: Keepalive packet loop-back detected on FastEthernet0/12.

020563: Oct 20 02:21:14.004 PDT: %PM-4-ERR_DISABLE: loopback error detected on Fa0/12, putting Fa0/12 in err-disable state

020564: Oct 20 02:21:16.048 PDT: %LINK-3-UPDOWN: Interface FastEthernet0/12, changed state to down

020565: Oct 20 02:21:43.196 PDT: %PM-4-ERR_RECOVER: Attempting to recover from loopback err-disable state on Fa0/12

Thank you,

[JORGE RODRIGUEZ]

Hi,

for your first question the disconnection can cause flapping state , in most cases duplex mismatch between switch port and cable modem.. Check into duplex settings at either end, if cable modem is not manageable the switch port should be set to auto for speed and duplex.

for the error disable loop back detection find out what connects to that port, there are quite few factors where ports shutdown, go to this link for background on error-disable ports and its causes.

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00806cd87b.shtml

HTH

Jorge

[uubozou11]

Thanks for your reply....why would a fe connection go up/down just suddenly then never again (as of yet)....could it be a slightly loose cable that got bumped or due to vibrations?

098422: Oct 24 00:50:15.227 PDT: %RTD-1-LINK_FLAP: FastEthernet0/1 link down/up 5 times per min

098424: Oct 24 00:50:25.225 PDT: %RTD-1-LINK_FLAP: FastEthernet0/1 link down/up 5 times per min

098425: Oct 24 00:50:30.303 PDT: %RTD-1-LINK_FLAP: FastEthernet0/1 link down/up 5 times per min

098426: Oct 24 00:52:37.483 PDT: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to up

098427: Oct 24 00:52:37.821 PDT: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to down

098428: Oct 24 00:52:41.693 PDT: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to up

098429: Oct 24 00:52:42.535 PDT: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to down

098430: Oct 24 00:52:44.640 PDT: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to up

[JORGE RODRIGUEZ · Accepted solution]

it is possible cabling, one way to tell is look at the switch port stats output and look for errors which are indicators of physical problems.. if you see errors clear counters and see if they increment change cables with new ones if possible, however, consecutive up/down grants to look into, look into what connects to fe0/1 and again dup settings matching is important.

to see port issue " show interfaces " or

" show interface fastethernet0/1"

to clear counters " clear counters " and watch for errors.

Rgds

Jorge