Switches don't talk to each other

[chicagotech]

We tried to connect two buildings using fiber cable. One building has Catalyst 3520 and other building has 3750. But they don't talk to each other.

To find out the problem, we bring these two switches in the same room and connect them directly with a 5 feet fiber cable. They still have the same problem. The following are what i try so far.

1. Connecting between two 3500 switches directly.

2. Connecting between 3750 and 3500 switches directly.

3. I also tried different fiber cable.

4. The sh int shows ?GigabitEthernet0/1 is down, line protocol is down?. What could be the problem?

[purohit_810]

Hi,

Have you check in 3750 or 3520... we can use either fiber or UTP port at 23 and 24.

If you are using 23 and 24 UTP... than STP will disable that ports.

Second, Have you checked SFP module. Please change it and check.

Third, r u able to connect by simple port with cross cable?

Regards,

Dharmesh Purohit

[rduke · Accepted solution]

I assume you already know this, but just in case:

1. Make sure you are connecting SX to SX transcievers. SX and LX use different wavelengths.

2. On "show interface" make sure the ports are not in an err-disabled state and that the media type says SX (or LX) instead of unknown or unsupported, etc.

3. Be careful to make sure all you fiber is the same. We recently had someone try to patch 62.5 on to 50 micron, and it would not work.

Randy

[chicagotech]

Thank you for the help

1. UTP 23 and 24 are not used.

2. I have tried 4 SFP modules.

3. simple port with cross cable works.

4. Between 3500 is SX to SX but not sure 3750. Since 3750 is using LC, I assume it is LX. but we have another other 3500 switch connects to the the same 3750. It works for over 1 year.

5. The command show interface on 3750 shows err-disabled. That could be the problem. The cable don't mark 62.5 or 50. How do you find it out?

sh interface from 3750:

GigabitEthernet1/0/28 is down, line protocol is down (err-disabled)

Hardware is Gigabit Ethernet, address is 0013.1935.bf1c (bia 0013.1935.bf1c)

MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Auto-duplex, Auto-speed

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

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

Last input never, output never, output hang never

Last clearing of "show interface" counters never

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 0 bits/sec, 0 packets/sec

0 packets input, 0 bytes, 0 no buffer

Received 0 broadcasts (0 multicast)

0 runts, 0 giants, 0 throttles

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

0 watchdog, 0 multicast, 0 pause input

0 input packets with dribble condition detected

0 packets output, 0 bytes, 0 underruns

0 output errors, 0 collisions, 3 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier, 0 PAUSE output

0 output buffer failures, 0 output buffers swapped out

sh interface from 3500

Hardware is Gigabit Ethernet, address is 0006.d751.d671 (bia 0006.d751.d671)

MTU 1500 bytes, BW 0 Kbit, DLY 0 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive not set

Auto-duplex , 1000Mb/s, media type is missing

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

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

Last input never, output 00:34:00, output hang never

Last clearing of "show interface" counters never

Queueing strategy: fifo

Output queue 0/40, 0 drops; input queue 0/75, 0 drops

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

7 packets input, 448 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

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

0 watchdog, 0 multicast, 0 pause input

11 packets output, 448 bytes, 0 underruns

0 output errors, 0 collisions, 1 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier, 0 pause output

0 output buffer failures, 0 output buffers swapped out

[purohit_810]

keepalive not set on 3500 switch.

Set keep alive on same port.

conf t

int gigabitethernet slot/port

keepalive 10

You problem solve, status will also change on 3750.

Regards,

Dharmesh Purohit

[rduke]

I am assuming it is not fixed yet. At this point I would disconnect the fiber. Enter configuration mode on that interface and issue a "shut" and "no shut" to clear the err-disabled interface (or just reload it). You should be able to read whether that tranceiver is long range or short range. LC is just the connector type, LX or SX run at different wavelengths. Another way to tell is that the SX are black, LX are blue on the part you use to pull out the SFP with.

Your switch should be able to read the transceiver type. It should also be logged when you install it.

Anyhow, show interface should indicate the type even if the link is down. See below:

GigabitEthernet1/0/28 is up, line protocol is up (connected)

Hardware is Gigabit Ethernet, address is 000e.838b.4d9c (bia 000e.838b.4d9c)

MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive not set

Full-duplex, 1000Mb/s, link type is auto, media type is 1000BaseLX SFP

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

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

Last input 00:00:00, output 00:00:18, output hang never

Last clearing of "show interface" counters never

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 1691000 bits/sec, 311 packets/sec

5 minute output rate 176000 bits/sec, 220 packets/sec

3677288427 packets input, 1905464436 bytes, 0 no buffer

Received 379962995 broadcasts (0 multicast)

0 runts, 0 giants, 0 throttles

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

0 watchdog, 266343468 multicast, 0 pause input

0 input packets with dribble condition detected

687408375 packets output, 366271263 bytes, 0 underruns

0 output errors, 0 collisions, 1 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier, 0 PAUSE output

0 output buffer failures, 0 output buffers swapped out

Randy

[chicagotech]

Thank you for all help. We had a consultant come to take look them. He could not fix it. He think it is hardware issue. He brought the two switches back to his office to test them. Will post back with the result.

By the way they are blue.

[rduke · Accepted solution]

By the way, the blues are long range. It is not recommended to use them on anything less than 10s of meters. Normall I swap them with SX when moving them side by side. Also, I have some 62.5 micron multimode that won't work without the mode conditioning patch cables (about $200 EA). Most of my fiber works OK with multimode but the LX on long multimode can be a big problem if you are unlucky enough to get some fiber susceptible to the problem.

Randy

[rtford31]

What type of transceiver are you using? If you are using an LX/LH transeiver part number GLC-LH-SM= and you are running it over 62.5um multi-mode fiber then you need a fiber conditioning cables on each end.

[chicagotech]

Update:

1. They found one of 3500 switches was broken and another one is good.

2. They brought the good one back. At beginning , the 3500 and 3750 don't talk to each other (no green light).

3. Finally, they found one of gbic in the 3750 switch was broken (the 3750 has 4 gibcs and two have been using for years). The problem is if they have the bad gbic in the switch 3750 doesn't talk to the 3500. After they took it out, both switches works.

Thank you for all inputs.