Why does Link-Flap occur? %LINEPROTO-5-UPDOWN , %LINK-3-UPDOWN

[JustTakeTheFirstStep]

Nov 25 17:24:57.519: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/4, changed state to down
Nov 25 17:24:58.522: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/4, changed state to down
Nov 25 17:25:06.083: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/4, changed state to up
Nov 25 17:25:07.082: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/4, changed state to up

Port	Align-Err	FCS-Err	Xmit-Err	Rcv-Err	UnderSize	OutDiscards
Gi1/0/1	0	2	0	3	0	0
Gi1/0/2	0	0	0	0	0	0
Gi1/0/3	0	0	0	0	0	0
Gi1/0/4	0	0	0	0	0	0
Gi1/0/5	0	0	0	0	0	0
Gi1/0/6	0	0	0	0	0	0
Gi1/0/7	0	0	0	0	0	0
Gi1/0/8	0	0	0	0	0	0
Gi1/0/9	0	0	0	0	0	0
Gi1/0/10	0	0	0	0	0	0
Gi1/0/11	0	0	0	0	0	0
Gi1/0/12	0	0	0	0	0	0
Gi1/0/13	0	0	0	0	0	0
Gi1/0/14	0	0	0	0	0	0
Gi1/0/15	0	0	0	0	0	0
Gi1/0/16	0	0	0	0	0	0
Gi1/0/17	0	0	0	0	0	0
Gi1/0/18	0	0	0	0	0	0
Gi1/0/19	0	0	0	0	0	0
Gi1/0/20	0	0	0	0	0	0
Gi1/0/21	0	0	0	0	0	0
Gi1/0/22	0	0	0	0	0	0
Gi1/0/23	0	0	0	0	0	0
Gi1/0/24	0	0	0	0	0	0
Gi1/0/25	0	0	0	0	0	0
Gi1/0/26	0	0	0	0	0	0
Gi1/0/27	0	0	0	0	0	0
Gi1/0/28	0	0	0	0	0	0
Port	Single-Col	Multi-Col	Late-Col	Excess-Col	Carri-Sen	Runts	Giants
Gi1/0/1	0	0	0	0	0	0	0
Gi1/0/2	0	0	0	0	0	0	0
Gi1/0/3	0	0	0	0	0	0	0
Gi1/0/4	0	0	0	0	0	0	0
Gi1/0/5	0	0	0	0	0	0	0
Gi1/0/6	0	0	0	0	0	0	0
Gi1/0/7	0	0	0	0	0	0	0
Gi1/0/8	0	0	0	0	0	0	0
Gi1/0/9	0	0	0	0	0	0	0
Gi1/0/10	0	0	0	0	0	0	0
Gi1/0/11	0	0	0	0	0	0	0
Gi1/0/12	0	0	0	0	0	0	0
Gi1/0/13	0	0	0	0	0	0	0
Gi1/0/14	0	0	0	0	0	0	0
Gi1/0/15	0	0	0	0	0	0	0
Gi1/0/16	0	0	0	0	0	0	0
Gi1/0/17	0	0	0	0	0	0	0
Gi1/0/18	0	0	0	0	0	0	0
Gi1/0/19	0	0	0	0	0	0	0
Gi1/0/20	0	0	0	0	0	0	0
Gi1/0/21	0	0	0	0	0	0	0
Gi1/0/22	0	0	0	0	0	0	0
Gi1/0/23	0	0	0	0	0	0	0
Gi1/0/24	0	0	0	0	0	0	0
Port	Single-Col	Multi-Col	Late-Col	Excess-Col	Carri-Sen	Runts	Giants
Gi1/0/25	0	0	0	0	0	0	0
Gi1/0/26	0	0	0	0	0	0	0
Gi1/0/27	0	0	0	0	0	0	0
Gi1/0/28	0	0	0	0	0	0	0

Incheon_1A-2_OA_SW_1#sh controllers e g1/0/4

Transmit GigabitEthernet1/0/4 Receive
3373280282 Bytes 600635403 Bytes
2229266075 Unicast frames 3955304360 Unicast frames
21818483 Multicast frames 12765 Multicast frames
17407667 Broadcast frames 965 Broadcast frames
0 Too old frames 599527471 Unicast bytes
0 Deferred frames 1046172 Multicast bytes
0 MTU exceeded frames 61760 Broadcast bytes
0 1 collision frames 0 Alignment errors
0 2 collision frames 0 FCS errors
0 3 collision frames 0 Oversize frames
0 4 collision frames 0 Undersize frames
0 5 collision frames 0 Collision fragments
0 6 collision frames
0 7 collision frames 1778248 Minimum size frames
0 8 collision frames 1459493747 65 to 127 byte frames
0 9 collision frames 263347989 128 to 255 byte frames
0 10 collision frames 833099650 256 to 511 byte frames
0 11 collision frames 234184930 512 to 1023 byte frames
0 12 collision frames 1163413526 1024 to 1518 byte frames
0 13 collision frames 0 Overrun frames
0 14 collision frames 0 Pause frames
0 15 collision frames
0 Excessive collisions 0 Symbol error frames
0 Late collisions 0 Invalid frames, too large
0 VLAN discard frames 0 Valid frames, too large
0 Excess defer frames 0 Invalid frames, too small
2218320348 64 byte frames 0 Valid frames, too small
44918853 127 byte frames
1445244 255 byte frames 0 Too old frames
1021966 511 byte frames 0 Valid oversize frames
382895 1023 byte frames 0 System FCS error frames
2402903 1518 byte frames 0 RxPortFifoFull drop frame
16 Too large frames
0 Good (1 coll) frames
0 Good (>1 coll) frames

I don't know what the connected equipment is.

Why does Link-Flap occur?

[marce1000]

 - Because the connecting device is continuously activating and de-activating it's network connection.

 M.

[Jaderson Pessoa]

It is because a device connected on this port is unstable. Is it a poe device? Normally is caused for a bad NIC.

[JustTakeTheFirstStep]

Not a POE device. I think there are too many Link-Flap interfaces to see as a NIC issue.

[Jaderson Pessoa]

could you share output from one interface that appear this isse?

show interface gix/x broadcast
show interface gix/x multicast
show interface gix/x unicast
show interface gix/x switchport
show interface gix/x status
show interface gix/x trunk
show interface gix/x

[julian.bendix]

Hi!

We would need to know what exactly is connected on that interface.

Best regards
Julian

[Leo Laohoo]

The above is "normal". Look at the time and date: It's is close to "beer-o'clock".
Some OS will go into "power saving" mode of and bring the link down/up/down/up when logging in, logging out or when the computer goes to "sleep".