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Interface flapping after bandwidth upgrade

Dear All,


After a bandwidth upgrade from 10 mpbs to 20 mbps, the interface keeps flapping intermittently on a nexus 5k switch. The switch is connected to 3750 located at another location. We could observe that cdp neighborship flap occurs only on the Nexus 5k switch and there are no logs observed on 3750 switch. Please hep as to what could cause the issue

Hall of Fame Super Gold

Post the output to the

Post the output to the command "sh interface <BLAH>" on both ends. 


The link between Nexus and 3750, is it copper or fibre optic? 


What is the exact model of the 3750?  Is it a plain FE, G, E or X?

Community Member

Hi Leo,Thank you for getting

Hi Leo,

Thank you for getting back with your questions.We are only observing  that the cdp neighborship flaps and comes up within 121 sec on Nexus 7k switches,without any link down alarms. However the customer faces a downtime during this period.No logs are observed on the 3750 switch


Is this possible, if only CDP flaps why should there be an outage during that period. The speed and duplex settings have been hardcoded to full and 100 mpbs


The link between Nexus and 3750, is it copper or fibre optic?

Fibre optic

The exact model is 3750e.


Show interface Ethernet2//2


R1##  sh int eth2/2

Ethernet2/2 is up

admin state is up, Dedicated Interface

  Hardware: 10/100/1000 Ethernet, address: 4055.4015.b674(bia 30e4.dbc1.05b0)

  Description: ***Connected to 3750  Internet Address is

  MTU 1500 bytes, BW 100000 Kbit, DLY 10 usec

  reliability 255/255, txload 11/255, rxload 28/255

  Encapsulation ARPA, medium is broadcast

  Port mode is routed

100 Mb/s  full-duplex,

  Beacon is turned off

  Auto-Negotiation is turned on

  Input flow-control is off, output flow-control is off

  Auto-mdix is turned on

  Switchport monitor is off

  EtherType is 0x8100

  EEE (efficient-ethernet) : n/a

  Last link flapped 2d17h

  Last clearing of "show interface" counters never

  4 interface resets

  Load-Interval #1: 30 seconds

    30 seconds input rate 11224580 bits/sec, 1112 packets/sec

    30 seconds output rate 4332124 bits/sec, 1140 packets/sec

  Load-Interval #2: 5 minute (300 seconds)

    300 seconds input rate 11433944 bits/sec, 1317 packets/sec

    300 seconds output rate 4060360 bits/sec, 1014 packets/sec

  L3 in Switched:

    ucast: 4673149810 pkts, 594555598148 bytes - mcast: 108 pkts, 7488 bytes

  L3 out Switched:

    ucast: 3000051974 pkts, 913035545316 bytes - mcast: 0 pkts, 0 bytes


    4674311181 unicast packets  71666 multicast packets  276 broadcast packets

    4674394567 input packets  5945608808888 bytes

    0 jumbo packets  0 storm suppression packets

    0 runts  0 giants  0 CRC/FCS  0 no buffer

    0 input error  0 short frame  0 overrun   0 underrun  0 ignored

    0 watchdog  0 bad etype drop  0 bad proto drop  0 if down drop

    0 input with dribble  0 input discard

    204 Rx pause


    3000206964 unicast packets  71523 multicast packets  23 broadcast packets

    3000278687 output packets  913067890991 bytes

    0 jumbo packets

    0 output error  0 collision  0 deferred  0 late collision

    0 lost carrier  0 no carrier  0 babble  0 output discard

    0 Tx pause


Hall of Fame Super Gold

No line errors received from

No line errors received from the 3750E.  So can you post the output to the command "sh interface <BLAH>" from the 3750E side?

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