Link flaps between two gigabit ethernet links

kaushik.phookan710 · ‎04-16-2015

Hi All,

We have two switches C3560G-48TS and C3750G-12S(is a stack switch). They are connected via two gigabit ethernet links bundled into a port channel. gi 0/47 & gi 0/48 of C3560G-48TS are connected to gi 1/0/3 & gi 2/0/3 resply. We have intermittent link flaps for only gi 0/47 connected to gi 1/0/3. Below is the log files from C3750G-12S and for C3560G-48TS logs are not showing.

So, requesting all to help me find the discrepancy, if it is somewhere. Appreciate your time.

C3750G-12S:
Apr 12 17:01:38.653 EDT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/3, changed state to up
Apr 12 17:02:22.225 EDT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/3, changed state to down
Apr 12 17:02:23.240 EDT: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/3, changed state to down
Apr 12 17:02:25.672 EDT: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/3, changed state to up
Apr 12 17:02:31.343 EDT: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/3, changed state to down
Apr 12 17:02:43.624 EDT: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/3, changed state to up

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Apr 12 17:02:49.480 EDT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/3, changed state to up

For C3560G-48TS: show interface cmd output:
sh int gi 0/47
GigabitEthernet0/47 is up, line protocol is up (connected)
MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 1000Mb/s, media type is 10/100/1000BaseTX
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters 7w4d
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 14000 bits/sec, 16 packets/sec
5 minute output rate 14000 bits/sec, 15 packets/sec
     258378059 packets input, 160471077187 bytes, 0 no buffer
     Received 33424530 broadcasts (8587908 multicasts)
     0 runts, 0 giants, 0 throttles
     476 input errors, 255 CRC, 0 frame, 0 overrun, 0 ignored

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C3750G-12S: show interface cmd output:
#sh int gi 1/0/3
GigabitEthernet1/0/3 is up, line protocol is up (connected)
MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive not set
Full-duplex, 1000Mb/s, link type is auto, media type is 10/100/1000BaseTX SFP
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:12, output 00:00:01, output hang never
Last clearing of "show interface" counters 7w4d
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 14000 bits/sec, 14 packets/sec
5 minute output rate 17000 bits/sec, 22 packets/sec
     648452143 packets input, 617654556023 bytes, 0 no buffer
     Received 1461988 broadcasts (712355 multicasts)
     0 runts, 0 giants, 0 throttles
     2 input errors, 1 CRC, 0 frame, 0 overrun, 0 ignored

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C3560G-48TS: interface config:

#sh run int gi 0/47
Building configuration...

Current configuration : 251 bytes
!
interface GigabitEthernet0/47
switchport trunk encapsulation dot1q
switchport trunk native vlan 999
switchport mode trunk
bandwidth 1000000
speed 1000
channel-group 16 mode active

C3750G-12S: interface config:

sh run int gi 1/0/3
Building configuration...

Current configuration : 338 bytes
!
interface GigabitEthernet1/0/3
switchport trunk encapsulation dot1q
switchport trunk native vlan 999
switchport mode trunk
srr-queue bandwidth share 10 10 60 20
queue-set 2
priority-queue out
mls qos trust dscp
auto qos voip trust
channel-group 16 mode active

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Madhukrishnan Gopinathan Nair · ‎04-16-2015

Hi kaushik,

I can see some input erros on gi0/47. So next step would be to check physical layer.

Try replacing cable, SFP etc on both sides.

Also regading 3560 not showing link down in logs, you may try enabling under gi1/0/3

logging event link-status

Hope this helps and kindly rate my post if it is useful to you.

Thanks,

Madhu.

kaushik.phookan710 · ‎04-16-2015

Hi Madhu,

Thanks for your reply. I will get the cables verified first and then go for SFP module. But the configuration of the interfaces, are they fine? I just have a little doubt about the manual configuration of bandwith and speed of GigabitEthernet0/47 of C3560G-48TS.

Also please note that the speed of C3560G-48TS's Gi0/47 is 100MB and Gi0/48 is 1000MB. And, since they were participating in etherchannel so speed of Gi0/47 has been changed about 1 year back, to 1000MB as can be seen in the configuration that I had provided above. So, is that also causing any type of issue?

Thanks for your time and help.