Traffic only going one way on Fiber Module

support systemsGo · ‎10-31-2013

Hello.

I have 2 switches connected via Cisco Fiber SFP module over a Layer 2 EtherMAN connection.

C3750 and C3750x

Both ports are configured with the same settings, however, a "sh int" command reveals that there are only output packets (no input packets).

This is happening on both connections. What can I try to fix it? See below for interface output and configuration.

Tried changing module to another spare one, and also confirmed with line provider that it is multimode and supports encapsulation.

GigabitEthernet1/0/28 is up, line protocol is up (connected)

Hardware is Gigabit Ethernet, address is xxxxxxxxxxxxxxxxx

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 force-up, media type is 1000BaseSX SFP

input flow-control is off, output flow-control is unsupported

ARP type: ARPA, ARP Timeout 04:00:00

Last input 2d08h, output 00:00:00, output hang never

Last clearing of "show interface" counters 01:39:48

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

30 second input rate 0 bits/sec, 0 packets/sec

30 second output rate 3000 bits/sec, 7 packets/sec

0 packets input, 0 bytes, 0 no buffer

Received 0 broadcasts (0 multicasts)

0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

0 watchdog, 0 multicast, 0 pause input

0 input packets with dribble condition detected

48510 packets output, 3735808 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier, 0 PAUSE output

0 output buffer failures, 0 output buffers swapped out

interface GigabitEthernet1/0/28

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 1,2,5,6,20

switchport mode trunk

switchport nonegotiate

load-interval 30

speed nonegotiate

srr-queue bandwidth share 1 30 35 5

queue-set 2

priority-queue out

mls qos trust cos

auto qos trust

devils_advocate · ‎10-31-2013

I assuming you have tried changing the cable itself?

Kyle McKay · ‎10-31-2013

This is most commonly seen when the fiber cable polarity is not reversed. Fiber connections do not support auto-MDIX like copper connections do.. that is, they cannot sense whether their neighbor port is transmitting and/or receiving and dynamically change to accommodate.

You must physically match the RX/TX fiber strands. Depending on which type of connector you are using (LC is most common) you would have to physically open it up and reverse the position of the two strands of fiber. This should correct your issue.

support systemsGo · ‎10-31-2013

Ok.

I will try chaning the RX and TX positions (cant remember if the cable connected would allow me to do that, since it the strand ends are encased in plastic together).

I'll also try changing the cable itself in a few hours, and let you know how it goes.

Most likely it is an issue on the 3750 end (not 3750x).

Just a note, earlier today, on the 3750x end, I tried connecting the TX on the right of the SFP port and the RX on the right, but got no connectivity light or status. But once I swapped it, it came right up.

Thanks again guys for the quick responses.

Leo Laohoo · ‎10-31-2013

Hmmm ... Layer 1 and Layer 2 is up on the interface. I've got a strange feeling this could either be a mis-configuration of the etherchannel (one way traffic) or you are running an IOS which has a bug.

support systemsGo · ‎10-31-2013

How would I test to see if it is a misconfiguration of etherchannel?

acampbell · ‎10-31-2013

Hi,

I agree with Leo.

If the interfaces are showing as up/up at both ends it seems very unlikely to

be a physical issue.

Can you post the configs from both ends

Regards,
Alex.
Please rate useful posts.

Regards, Alex. Please rate useful posts.

Leo Laohoo · ‎10-31-2013

How would I test to see if it is a misconfiguration of etherchannel?

The most common culprit could be someone did NOT configure etherchannel. It's like someone connected both links as individual uplink. So one traffic goes one port and the return traffic comes from another port.

support systemsGo · ‎10-31-2013

Ok.

Could you give me an example of what I would need to configure on the switch on each end to get the etherchannel going?

Leo Laohoo · ‎10-31-2013

Could you give me an example of what I would need to configure on the switch on each end to get the etherchannel going?

I think I'm going way too ahead of myself.

Can you confirm that the link between both switches? Can you confirm there's only ONE link? Can you post the following output:

1. sh cdp neighbor;

2. sh interface trunk

support systemsGo · ‎10-31-2013

I can get the output for you in a little while.

But what I can tell you is that there is another working EtherMAN link between these 2 switches, except that this link is only 100Mbps and it is copper. (Same line provider as fiber line that is having issue.)

Port config is same as above config, except speed manually set to 100 and duplex manually set to full.

Last time sh cdp neighbor showed the switches on the copper link, but nothing for the fiber.

support systemsGo · ‎10-31-2013

Output from 3750 end:

coresw#sh cdp nei

Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge

S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone,

D - Remote, C - CVTA, M - Two-port Mac Relay

Device ID Local Intrfce Holdtme Capability Platform Port ID

aplcucm1.localdomain

Gig 1/0/7 143 H 7835I3 eth0

SW05.test.com

Gig 1/0/22 153 S I WS-C2960S Gig 1/0/47

SW02.test.com

Gig 1/0/23 156 S I WS-C2960S Gig 1/0/49

SW02.test.com

Gig 2/0/23 156 S I WS-C2960S Gig 1/0/50

SW01.test.com

Gig 1/0/24 177 S I WS-C2960S Gig 1/0/49

SW01.test.com

Gig 2/0/24 177 S I WS-C2960S Gig 1/0/50

aplcucm2 Gig 1/0/10 125 H Cisco-MCS eth0

kvh-coresw.test.com

Gig 2/0/26 122 R S I WS-C3750X Gig 2/0/24

rtr02.test.com

Gig 2/0/18 153 R S I 1812W-P Fas 9

rtr02.test.com

Gig 2/0/15 163 R S I 1812W-P Fas 1

rtr01.test.com

Device ID Local Intrfce Holdtme Capability Platform Port ID

Gig 1/0/18 127 R S I 1812W-P Fas 9

rtr01.test.com

Gig 1/0/15 157 R S I 1812W-P Fas 1

VGW01.test.com

Gig 1/0/2 151 R S I CISCO2911 Gig 0/1

VGW01.test.com

Gig 2/0/2 151 R S I CISCO2911 Gig 0/2

VGW02.test.com

Gig 2/0/8 153 R S I CISCO2911 Gig 0/2

coresw#sh interface trunk

Port Mode Encapsulation Status Native vlan

Gi1/0/1 on 802.1q trunking 1

Gi1/0/28 on 802.1q trunking 1

Gi2/0/1 on 802.1q trunking 1

Gi2/0/22 on 802.1q trunking 1

Gi2/0/26 on 802.1q trunking 1

Po1 on 802.1q trunking 1

Po2 on 802.1q trunking 1

Po3 on 802.1q trunking 1

Po5 on 802.1q trunking 1

Port Vlans allowed on trunk

Gi1/0/1 13,200

Gi1/0/28 1-2,5-6,20

Gi2/0/1 13,20,200

Gi2/0/22 1-2,5-6,20,200

Gi2/0/26 1-2,5-6,20

Po1 1-2,5-6,20

Po2 1-2,5-6,20

Po3 1-2,5-6,20,200

Po5 1-2,5-6,20

Port Vlans allowed and active in management domain

Gi1/0/1 13,200

Gi1/0/28 1-2,5-6,20

Gi2/0/1 13,20,200

Gi2/0/22 1-2,5-6,20,200

Gi2/0/26 1-2,5-6,20

Po1 1-2,5-6,20

Po2 1-2,5-6,20

Po3 1-2,5-6,20,200

Po5 1-2,5-6,20

Port Vlans in spanning tree forwarding state and not pruned

Gi1/0/1 13,200

Gi1/0/28 1-2,5-6,20

Gi2/0/1 13,20,200

Gi2/0/22 1-2,5-6,20,200

Gi2/0/26 1-2,5-6,20

Po1 1-2,5-6,20

Po2 1-2,5-6,20

Po3 1-2,5-6,20,200

Po5 1-2,5-6,20

coresw#

Output from 3750x end:

coresw#sh cdp nei

Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge

S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone,

D - Remote, C - CVTA, M - Two-port Mac Relay

Device ID Local Intrfce Holdtme Capability Platform Port ID

coresw.test.com

Gig 2/0/24 145 R S I WS-C3750G Gig 2/0/26

coresw#sh interface trunk

Port Mode Encapsulation Status Native vlan

Gi1/1/1 on 802.1q trunking 1

Gi2/0/24 on 802.1q trunking 1

Port Vlans allowed on trunk

Gi1/1/1 1-2,5-6,20

Gi2/0/24 1-2,5-6,20

Port Vlans allowed and active in management domain

Gi1/1/1 1-2,5-6,20

Gi2/0/24 1-2,5-6,20

Port Vlans in spanning tree forwarding state and not pruned

Gi1/1/1 1-2,5-6,20

Gi2/0/24 1-2,5-6,20

coresw#

Notes

3750 end - Fiber port is 1/0/28, copper port is 2/0/26

3750x end - Fiber port is 1/1/1, copper port is 2/0/24

Leo Laohoo · ‎11-01-2013

3750 end - Fiber port is 1/0/28, copper port is 2/0/26

3750x end - Fiber port is 1/1/1, copper port is 2/0/24

Judging from the output, I'd say ports 1/0/28 and 2/0/26 are in a etherchannel, possibly Po 1, Po 2 or Po 5. Can't determine which one until you furnish the output "sh etherchannel <1, 2 or 5> summary".

However, in the 3750X side, there's no ethernchannel being configured. So I guess this does support my theory that you are getting asymetric traffic due to etherchannel misconfiguration.

support systemsGo · ‎11-06-2013

I will get you the output soon.

But I did find that if I removed the qos from the fiber line, it comes up.

aabhatia2012 · ‎08-01-2016

i also see the same issue on my switches. nothing on fiber copper comes up ok.

if i shut down fiber port on one switch the other end shows down too but not vice versa if i shut down port on switch 2, switch 1 port still shows up.

nothing coming in sh cdp nei

SYD1-ACCS-1101#sh cdp nei | ex Phone
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
D - Remote, C - CVTA, M - Two-port Mac Relay

Device ID Local Intrfce Holdtme Capability Platform Port ID
SYD1-CORR-001.executiveboard.com
Gig 2/0/48 130 R S I WS-C4507R Gig 5/46
SYD1-CORR-001.executiveboard.com
Gig 1/0/48 130 R S I WS-C4507R Gig 2/46