Guide
Transceivers and cables – what fits?
The wrong module is one of the most common reasons a delivery cannot be put into service right away. Here is how to choose correctly from the start.
Short answer
Choose the transceiver by the port, the fibre and the distance. The port decides form factor and speed (SFP 1G, SFP+ 10G, SFP28 25G, QSFP 40/100G). Multimode fibre with SR modules is enough within a building, single-mode with LR up to 10 km between buildings. Between two switches in the same rack a DAC cable is simplest and cheapest.
Which three things must match?
A transceiver must match speed, form factor and reach.
- Speed: 1G (SFP), 10G (SFP+), 25G (SFP28), 40G/100G (QSFP+/QSFP28)
- Form factor: the switch port decides – an SFP+ port takes SFP or SFP+, not QSFP
- Reach: SR for multimode fibre within the building, LR for single-mode up to 10 km
What do you use within the same rack?
To connect two switches in the same rack, a DAC (direct attach) cable is almost always cheaper and simpler than two transceivers and a fibre. It has the modules built into the cable and comes passive (CU) in 1–5 metres and active (ACU) in 7–10 metres.
What do the suffixes in the name mean?
The suffix gives the fibre type and reach. That is what must match the fibre in the building.
- SX / SR – multimode fibre, short reach within the building (a few hundred metres)
- LX / LH / LR – single-mode fibre up to about 10 km
- ER / ZR – single-mode for longer distances (40–80 km)
- T / TE – copper port (RJ45) in an SFP slot
- BX-U / BX-D – BiDi: a single fibre, ordered in pairs (one U and one D)
- CU / ACU – copper DAC cable; AOC – active optical cable
- -S – Cisco's standard variant (most common); -I – for industrial temperatures
Do the same modules work in Catalyst 1200/1300 and Meraki?
Catalyst 1200 and 1300 take the small-business MGBSX1, MGBLX1 and MGBT1 modules but also many of Cisco's standard GLC and SFP-10G optics and DAC cables. Meraki MS switches and MX firewalls are certified with the Meraki modules (MA-SFP-…); cloud-managed Catalyst switches take Cisco's standard optics. When you add a product to the basket we suggest modules that fit.
Read more: Uplink modules – which one?
Original or third party?
We sell original modules through authorised distribution. Third-party modules are cheaper but can lead to support discussions with the manufacturer when something fails. For core and data centre networks we recommend originals.
Conclusion
How we would choose
Common choices:
10GBASE-SR SFP Module Enterprise Class
10G over multimode fibre within the building – the most common choice.
10GBASE-LR SFP Module Enterprise Class
10G over single-mode fibre between buildings.
10GBASE-CU SFP+ Cable 1 Meter
10G between two switches in the same rack.
Frequently asked questions
Questions we often get
How do I know which fibre is already in the building?
Multimode is usually orange or aqua, single-mode yellow. If you are unsure, send a photo of the connector and the documentation and we will help.
Can I use 10G modules in a 1G port?
No. However, most 10G ports can run 1G modules, which is handy when upgrading step by step.
Must the modules at both ends be the same?
They must have the same speed and the same type, e.g. SR to SR on multimode. The exception is BiDi modules, which are ordered in pairs with one U and one D module. Remember to count one module per end.