How is this possible!! I have 2 buildings connected by fiber, it was setup sometime ago, long before I started. I have a 3550 connected to a 2950. The buildings are about 6 miles apart. The connection went down last night and I got it back up right away by switching interfaces on the 2950 from gi0/1 to gi0/2. The connection came right up. But my question is, at the 3550, when I do a sho int status, it says the gbic is a ZX. At the 2950, it says the gbic is a LX. How is this working???
From the Data Sheet:
CISCO 1000BASE-LX/LH GBIC
The Cisco 1000BASE-LX/LH GBIC (WS-G5486) fully complies with the IEEE 802.3z 1000BASE-LX standard. However, its higher optical quality allows it to reach 6.2 miles (10 kilometers) over single-mode fiber (SMF), compared with the 3.1 miles (5 km) specified in the standard.
CISCO 1000BASE-ZX GBIC
The Cisco 1000BASE-ZX GBIC (WS-G5487) operates on ordinary single-mode fiber optic link spans up to 43.4 miles (70 km) long. Link spans of up to 62 miles (100 km) are possible using premium single-mode fiber or dispersion shifted single-mode fiber. The GBIC provides an optical link budget of 23 dB-the precise link span length will depend on multiple factors such as fiber quality, number of splices, and connectors.
When shorter distances of single-mode fiber are used, it might be necessary to insert an in-line optical attenuator in the link to avoid overloading the receiver:
NOTE: A 5-dB or 10-dB inline optical attenuator should be inserted between the fiber-optic cable plant and the receiving port on the Cisco 1000BASE-ZX GBIC at each end of the link whenever the fiber-optic cable span is less than 15.5 miles (25 km).
It looks like they both work OK with SM fiber.
LX is 1310 and ZX is 1550 which is also OK since (most) all Cisco RX optics are wide-band.
One thing you might check is the RX power to make sure the leves are within the spec.