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New Member

Odd routing problem?

I've got an odd problem that I'm not sure is a routing issue or something else.

I have a Free Space Optic(FSO) link that I need to relocate from one switch to another.

The link is currently attached to a 3524XL through a gigabit fiber GBIC.

The 3524XL is part of a stack of five 3524XL's that, in turn, attach to a 3750E on a different floor via another fiber GBIC/SFP connection on the building's fiber backbone.

When I attach the FSO directly to the 3750E via the building's fiber backbone, the SFP on the 3750E shows a solid link, but there is zero traffic through the connection.

All the ports involved are configured as dot1q trunks.

I left the new configuration connected for about 20 minutes without change.
When I reconnected the FSO to the 3524XL, the link worked almost instantly.

The port configurations are very basic:

3524XL port settings:
interface GigabitEthernet0/2
no flowcontrol
switchport trunk encapsulation dot1q
switchport mode trunk

3750E port settings:
interface GigabitEthernet1/0/52
description UT FSO Link
switchport trunk encapsulation dot1q
switchport mode trunk

Any ideas as to where to start troubleshooting would be appreciated.

New Member

Re: Odd routing problem?

Double check if the duplex & speed is matching in both sides.



New Member

Re: Odd routing problem?

Have you checked that the GBIC you are using in the 3750 is good?

Also, the port itself could be bad in the 3750. Set up a test link with that port and another gbic and see if you get a link to a test port in another switch.

Hall of Fame Super Silver

Re: Odd routing problem?


I wonder if it is significant that on the 3524XL you have configured no flow-control but on the 3750E you have not configured this?



New Member

Re: Odd routing problem?

Thank you all for your input.

Dasuntha: My original post included the configuration of the ports.
Neither have any commands regarding speed and duplex.
Since both the GBIC port of the 3524 and the SFP port of the 3750E are GbE, they're both auto/auto by default.
I did check that however, and both ports showed a status of Gigabit/full duplex.

Good thought.
I have used different SFP's on that particular port with the same result.
I have not, however, tried using that particular port to connect to anything else.
I will try that tomorrow to confirm that both the SFP and the port it's in will connect to another switch without issue.

That is the default setting on the GBIC ports of a 3524XL.

Flow control is a traffic shaping method that predates QoS.
I've never seen any of my 3524's (I have about 15 of them in use) set any other way.
Additionally, the flow control is a throttling mechanism, and doesn't ever cut off data flow.
If it was causing issues, I would still see traffic.

New Member

Re: Odd routing problem?

A bad SFP port on a router can be tricky. We just had a similar situation here. You go into all kinds of detail on the port setup and the routing and then it all comes back to being a layer 1 issue. Aaarrrrrr! Anyway, let us know how this turns out.