Physical Fiber Connection Issue

[jeremiah.nelson]

Hello.  I am trying to get a Cisco 3750g and a Hirschman rs30 to communicate through fiber.  For some reason I cannot even get link lights.  This means physical connection issue to me.  I am using known working sfp modules and a known working fiber jumper.  I can get the ports to work as long as I go Cisco to Cisco or Hirschman to Hirshman.  I have tried MM and SM jumpers (all known working).  I have switched polarities on the fiber.  I can connect via copper just fine as long as I force the speed to 100mb.  The speed on the hirschman fiber port is 1000mb.  I assume I would have to force the speed to 1000mb on the Cisco but do not know how as the only "speed" command option is "nonegotiate".  If anyone has ever worked with these and has pointers I'd appreciate it.

Jeremiah Nelson

[samavedula_rama]

Yes. On Cisco Gigabit Fiber port, you can only ask it to either negotiate or not.

You should try to use "speed nonegotiate" and see what happens. Also, do you have a media converter in between both the switches?

[jeremiah.nelson]

Thank you for the response.  I have tried the command "speed nonegotiate" and still no link lights.  I do not have a media converter in between the 2.  There is only a single fiber jumper.  The total distance is about 6 feet.  Any ideas?

Jeremiah Nelson

[Antonio Knox]

A few of things to check:

-Try swapping the pairs.  The Tx may be where the Rx should be and vice versa.  This is a common issue when connecting new fiber.

-Make sure that 'no shut' is configured on the link

-Ensure that the configrations are a match at both ends (native vlan, encapsulation, mode)

If no joy, post back here, and we'll dig deeper.

[jeremiah.nelson]

Here is the config for the copper port that is working fine.

interface GigabitEthernet1/0/48
description test trunk to Hirschmann
switchport access vlan 209
switchport trunk encapsulation dot1q
switchport trunk native vlan 209
switchport trunk allowed vlan 1,209
switchport mode trunk
speed 100
end

Here is the corresponding config on the Hirschmann copper port.

interface  1/1
exit

Here is the config on the fiber port.

interface GigabitEthernet1/0/52
description test fiber trunk to Hirschmann
switchport access vlan 209
switchport trunk encapsulation dot1q
switchport trunk native vlan 209
switchport trunk allowed vlan 1,209
switchport mode trunk
speed nonegotiate
end

Here is the the config on the Hirschmann Fiber port.

interface  1/2
exit

Would setting a vlan on the Hirschmann show a link light?  I tried switching the polarity on the fiber multiple times and still no link lights of any sort.

Jeremiah Nelson

[Antonio Knox]

Place this config on the Hirschmann Fiber port.

interface GigabitEthernet1/2
switchport access vlan 209
switchport trunk encapsulation dot1q
switchport trunk native vlan 209
switchport trunk allowed vlan 1,209
switchport mode trunk
no shut

Also, though this part is not a link issue, make sure your VTP config is correct so that you don't have vlan problems.

[jeremiah.nelson]

I guess I'm not understanding why the copper connection works but the fiber doesn't?

Jeremiah Nelson

[Antonio Knox · Accepted solution]

Typically, with fiber it's a physical issue.  Here are some more things to check:

• on each switch, run this command 'sh int gi2/14 | i media'  your output should look like this

          Full-duplex, 1000Mb/s, media type is LH  <----this could also read SX, either way it should MATCH on both switches. 

If it doesn't then you need to find out which one you should be using, and make sure you have the same on both ends.  Also, this is what you need in both cases:

• If SX, you will need MM cabling.
• If LH, you will need SM (or MM with mode conditioning, depending on the length of the run)

It would be best to not attempt to equate the operation of a copper run to a fiber run.  They are technically and fundamentally apples and oranges.  You may confuse yourself if you attempt to base operation of on the other.  Fiber can work or not work in conditions different from copper and vice versa.

Message was edited by: Antonio Knox

[jeremiah.nelson]

I don't know the commands to show that information on a hirschmann switch.  I am closing the post for now as I was pulled to work on something else and will have to revisit this issue at a later time.

Thank you for the assistance though.

Jeremiah Nelson

[Viper2000]

Hi Everyone

I had the same problem and solve it by disabling IGMP snooping on the Cisco.

Regards

Johan Robbetze

[parmstrong]

Disabling IGMP globally on the switch resolved this issue for me, as well.
no ip igmp snooping - config mode.

I have a: WS-C3750G-12S with a FastE SFP inserted into a gig interface.

<< Per capabilities >>
GigabitEthernet2/0/3
Model: WS-C3750G-12S
Type: 100BaseFX SFP
Trunk encap. type: 802.1Q,ISL
Trunk mode: on,off,desirable,nonegotiate
Channel: yes
Broadcast suppression: percentage(0-100)
Flowcontrol: rx-(off,on,desired),tx-(none)
Fast Start: yes
QoS scheduling: rx-(not configurable on per port basis),
tx-(4q3t) (3t: Two configurable values and one fixed.)
CoS rewrite: yes
ToS rewrite: yes
UDLD: yes
Inline power: no
SPAN: source/destination
PortSecure: yes
Dot1x: yes

<< Per Interface >>
GigabitEthernet2/0/3 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is 0018.19da.9703 (bia 0018.19da.9703)
Description: ** Conn To Hirschman RS20 Switch **
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive not set
Half-duplex, 100Mb/s, link type is auto, media type is 100BaseFX SFP
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input never, output 00:00:00, output hang never
Last clearing of "show interface" counters 05:07:00
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 0 bits/sec, 0 packets/sec
5 minute output rate 21000 bits/sec, 30 packets/sec
0 packets input, 38040 bytes, 0 no buffer
Received 0 broadcasts (0 multicasts)
0 runts, 0 giants, 0 throttles
58 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
15011 packets output, 1272719 bytes, 0 underruns
20 output errors, 38 collisions, 17 interface resets
0 babbles, 5 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 PAUSE output
0 output buffer failures, 0 output buffers swapped out

<< My interface config >>
interface GigabitEthernet2/0/3
description ** Conn To Hirschman RS20 Switch **
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,129-134,1002-1005
switchport mode trunk
switchport nonegotiate