3550-24 Keeps 'disapperaring'

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Jun 25th, 2008
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I have a cisco 3550-24 that in periods keeps disappearing. friday-saturday: 148 times, yesterday-today: 45 times. Monday:zero.

The worst thing is that I can't get to it, it's locked inside a building I'm not allowed to set foot in. To do physical work, I have to order a techician to open the room and to do my work. That costs about $400-700. So I want to see if I can solve it from here. It's connected through fibre on a fastethernet port (2/21)on a 4503 I have locally. On the south end is a fibreconverter, and an ethernet cable going to fa0/24 on the 3550.

It has a simple configuration, customer vlan's through a trunk, a management vlan, and no routing. So it's a simple switch.

I can choose from full or half duplex, tried both on both ends, in addition to auto in the 3550 end.

the 4503 interface has this to say about errors:

169 input errors, 132 CRC

The 3550 has this to say: 12 input errors, 12 CRC.

I've upgraded software to 12.2-20, so the uptime isn't more than a couple of hours on the 3550.

But when it disappears, the uptime stays solid, so it doesn't reboot when it's 'away'.

I have interface snmp alerting turned on on the 4503, and it's never down when the 3550 is away. So the link doesn't go down. That makes me believe that the fibreconverter is allright as well.

When I try to transfer an image over tftp, it's very slow. (100mbit all the way, compared to other switches in my network, maybe 10 times as slow.) And the crc counter on the 4503 increases by a lot.

I've tried to connect it to another 3550 at my end via a fibreconverter, but the same result there as well. I haven't got a clue what to do, except buy a new switch, and pay someone to change it for me. But I don't want that.

Suggestions would be deeply appreciated.



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Kevin Dorrell Wed, 06/25/2008 - 06:05
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Is the fibre connection on 1000BaseSX GBICs? If so, change them, at both ends. The SX components are notoriously unreliable, and tend to drift with time.

If you have the fibreconverter that you are using for testing, swap it with the one in production. You might find the problem goes away. At least you could eliminate that from your diagnosis.

Tell us more about the fibreconverter. I suspect problem may be hidden in there. Do you have a spec for it?

Kevin Dorrell


markraves Wed, 06/25/2008 - 06:51
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Thnaks for reply.

The fibre converter is a MC110TSC. And it's 100Mbit. The converter is also within the room I can't get to, so I can't change it either, this has been working for the last three years. If I could get into the room, I would instantly swap it with a cisco gbic and replace the fastethernet port on my end with a lx sfp. But, I can't do that, since I can't get into the room. I was hoping it was a soft error which was possible to fix without physically beeing there.


glen.grant Wed, 06/25/2008 - 06:57
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I would suspect the fiber converters or the fiber itself . Just by your descriptions sounds like one or the other . You are going to have to get your hands or have someone test the fiber for loss . if you can replace the converters . If it is a fiber converter you probably won't see it go down because it is just looking at a short ethernet connection between the switch and the converter so unless you lose power to the converter that link will never show down. Does it drop a lot of packets when you do a extended ping across the link with large packets like 1400 ? To me it does not sounds like a switch problem .

markraves Wed, 06/25/2008 - 10:59
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Well, first of all it's only one fibre converter, since I use a sfp at my end. That would lead me to believe that the fibre converter is ok, since the 4503 with the sfp is directly connected to the converter. (and never goes down) That's why I don't think it's the fibre converter itself. I have tested for db loss on the fibre, though only with the signal that the fibre converter is sending. But it is more than sufficient to maintain the link at 22km. The fibre is actually very good.

though since I can't get to the other end, I can't test both of the leads, since nr. two isn't sending, only recieving. But, in my years in the fibre business, VERY seldom is a sm fibre a problem. the loss you get is insignificant, especially in so short distances. Besides, the equipment used when splicing measures the loss over the splice, and it's downright minimal compared to the old mm fibres.

But anyhow. I think I have a solution. I use another 3550 somewhere else, and I'm going to replace that one with a pensioner, a 3524xl.

Then I'll pay to have the 3550 switched, and in the same time, throw away the fibre converter and plug it directly to the 4500's management card.

Then I've got time to thoroughly test the 3550 and come up with a solution. (or buy a new) Seems there is no way around paying someone to enter the room.

You'd think it's the queens bloody bedroom.



h.parsons Wed, 06/25/2008 - 12:43
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What model SFP are you using on the 4503 side? 22km is a pretty good distance.

markraves Thu, 06/26/2008 - 01:53
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Thanks for input.

It's just an ordinary 3rd part 100FE sfp.

I didn't think of this because I have customers on farther distances than that (up to 29km.) with the same sfp. completely without problems.

But I shall try to find another converter and test further.




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