12-19-2007 06:55 PM - edited 03-05-2019 08:05 PM
I have a trunk connecting my 3750G switch with a Fiber ZX SFP module:
Model: WS-C3750G-24PS
Type: 1000BaseZX SFP
connecting to a ZX SFP on a 6506 switch.
On 3750G
interface GigabitEthernet1/0/25
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 120
switchport mode trunk
speed nonegotiate
If I set the speed to "no speed nonegotiate", the link does not come up at all. If I set "speed nonegotiate", the link flaps as seen below.
5w2d: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/25, changed state to down
xxx#
5w2d: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/25, changed state to up
xxx#
5w2d: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/25, changed state to down
xxx#
5w2d: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/25, changed state to up
xxx#
5w2d: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/25, changed state to down
xxx#
5w2d: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/25, changed state to up
xxx#
5w2d: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/25, changed state to down
xxx#
5w2d: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/25, changed state to up
The config on both sides is the same. I have tried all different combinations of speed on both sides.
speed nonegotiate with negotiate
speed nonegotiate with nonegotiate
no speed nonegotiate with negotiate
no speed nonegotiate with nonegotiate
I cant get this link to come up.
Can this have anything to do with spanning-tree?
Any help ?
12-19-2007 07:27 PM
Spanning tree won't cause this to happen. The line protocol refers to the actual ethernet link establishment (so even if STP put this port in the block/discard state, the line would remain up)
In this case, I'd try another SFP or check out my fiber. This looks like a layer 1 issue at first review.
12-19-2007 08:13 PM
That was my guess also. I will try and reseat the fiber and sfp tomorrow.
12-19-2007 08:26 PM
How long is the fiber run between the two switches? I connected a 6509 and 4510 with the ZX SFPs, and after a 12km run was only at -1db of loss. I remember reading that Cisco recommends if you have anything less then -8 to add a 10db attenuator to the link.
12-22-2007 01:54 PM
Good point, Everest. Cisco says that if there is less than 8db of total attenuation that you should add a 10db attenuator (because the SFP will shoot between 5 and 0 db). In this case, I'd, optimally, measure the power on the fiber and see if I need to add the attenuator. If you can't measure the power, add the attenuator and see if that doesn't solve your problem.
If you add the attenuator and the problem is still there, the SFPs may be dead from receiving too much power.
(Source: http://www.cisco.com/en/US/products/hw/modules/ps5455/products_data_sheet0900aecd8033f885.html)
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