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New Member

Line Protocol change state up / down


I have got many connections in fiber mode (LX connections) between 4506 and 2950-48G or 2950-24G.

On one of this connection, once time by day, random time of the day, the

GigaEthernet 0/1 from the 2950 pass to down during 3 seconds and pass up again only on the 2950 side.

We can see that inside the show log and inside the LMS console .

We have change the GBICs connectors and LX fiber without successfull solution.

We use RSTP.

What can be the problem so ?

Hardware failure again ? Connection hardware failure ?

Problem of fibers?

The version of 4506 is 12.1.14E and the version of 2950 is 12.1.13.

Any ideas are welcome.

New Member

Re: Line Protocol change state up / down


This could depend of many things, but heres some ideas:


When running LX on MMF, you must think about the length of the fiber.

When in an interval (see the link) you may need a patchcable conditioner.


Check the logs on all switches for convergens of SPT. See that you have spanningtree portfast on ports with clients. Configure the root and secondary root hard manually.


Upgrade the switches to the latest version.

New Member

Re: Line Protocol change state up / down

Thx you for your answer.

1) We respect the lenght for LX.

2) There is no change on RTSP topologie. The port that is up/down is a blocking force port.

3) On the 4506 it's the last version.

On the 2950 it's not really possible to upgrade to the last version actually :/

It's really strange problem. :|


Re: Line Protocol change state up / down

Time to sniff the wire at that time to determine the sequence of events leading to the line bounce

New Member

Re: Line Protocol change state up / down

Thank you for the idea.

I note your answer and i will do it the next time that it fail.


New Member

Re: Line Protocol change state up / down


I update this post because i have find interesting something inside interfaces.

For exemple :

GigabitEthernet4/4 is up, line protocol is up (connected)

Hardware is Gigabit Ethernet Port, address is 0007.eb98.2635 (bia 0007.eb98.26


Description: Lien F-SX Vers 3550-DS-01

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)

Unknown duplex, 1000Mb/s, link type is auto, media type is SX

output flow-control is unsupported, input flow-control is unsupported, 1000Mb/


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

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

Last input 00:00:01, output never, output hang never

Last clearing of "show interface" counters never

Input queue: 0/2000/0/0 (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 1000 bits/sec, 1 packets/sec

476907 packets input, 83340720 bytes, 0 no buffer

Received 224223 broadcasts (0 multicast)

0 runts, 0 giants, 0 throttles

4335 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

0 input packets with dribble condition detected

2010321 packets output, 273455215 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 output buffer failures, 0 output buffers swapped out

What means input errors?

Best regards.

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