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Having an ethernet crossover cable it is possible to make a lan, connecting both devices directly with no need of a router or switch. Of course it needs some configuration.

The question is: Is it possible to achieve that using fibre cable? Do we need a crossover fibre cable? Does it matter the connector? What if one of them is 10GbE and the other is GbE?

The idea is to make a direct connection between two servers using a specific fibre network card. One of them is a backup and data server we want out of our lan.

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  • A fiber optic cable can also be an ethernet cable. Ethernet runs on a variety of media, from coaxial cable to fiber optic cable. The cable of any one medium used for ethernet is an ethernet cable.
    – Ron Maupin
    Aug 24 '20 at 12:45
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Having an ethernet crossover cable it is possible to make a lan, connecting both devices directly with no need of a router or switch.

For twisted-pair Ethernet, most devices support Auto MDI-X today, making crossover cables redundant.

The question is: Is it possible to achieve that using fibre cable?

Yes. In contrast to twisted-pair cabling which is "straight" by standard, crossover is the rule for fiber connections. So, you can simply connect two fiber ports with a patch cable or a patch-plenum-patch run without problems. Many fiber patch cables can also be configured for a 1:1 or a crossover connection.

Many devices have SFP (1G) or SFP+ (10G) ports that allow you to fit an optical module as required. Generally, the module types at either end must match. Some SFP+/10G modules allow you to connect to an SFP/1G module, but that is not the rule. In either case, wavelength (-S/-L) and fiber type (single-mode or multi-mode) must always match.

Does it matter the connector?

The cable connector needs to match the device connector on that side. While LC connectors are pretty much standard today, SC or even ST connectors are still widespread. Simply buy/use a cable that has the connectors you need.

What if one of them is 10GbE and the other is GbE?

Most 10G ports require you to fit a 1G module to connect to a GE port. Some port/module combinations ("dual speed") may be downward compatible (10GBASE-SR -> 1000BASE-SX; 10GBASE-LR -> 1000BASE-LX), but that depends on your equipment - check the specs. Some 10G ports won't even connect to 1G at all.

The idea is to make a direct connection between two servers using a specific fibre network card. One of them is a backup and data server we want out of our lan.

That'll work, using compatible SFP+ modules and cables. Note that some NIC vendors try to force you to use "original" modules. For almost all brands there's a large market for "100% compatible" modules though, so you don't really need to pay premium prices.

For very short range (<=7 m), a budget alternative to 10GBASE-SR is direct-attach copper (DAC) which, again, needs to be compatible with your NICs (or switches). The SFP+ modules on DACs are integrated into the cable and cannot be unplugged. With vendor lock-in, that requires you to have compatible devices at either end unless you buy or program special adapter DACs.

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Yes, you can do this with equal-speed fiber transceivers which support the same transmission type. For example, if each PC has a 1000baseLX SFP, you can simply connect a single-mode patch cord between those PCs and it will work.

You've asked about a crossover cable. Optical cables are generally easy to roll at one end -- swap the two fibers into each-others' position on the connector. You don't need a special cable. Here's a YouTube video demonstrating the process.

You can't connect a 1 GbE optical transceiver to a 10 GbE one. Also, you can't connect a 1000baseLX (single-mode, 1310nm) transceiver to a 1000baseSX (multi-mode, 850nm) one. The transceivers need to be of the same type and speed, and be compatible with the available cabling.

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