Cisco GLC-BX, 100FX and 100LX: Match Rate, Fiber and the Far End

Start with the installed link

A replacement that fits the SFP cage can still be the wrong optic. Read the label on both ends, record the switch and port numbers, and identify single-mode or multimode fiber before selecting a part. Preserve the full ordering string, including the final equals sign and any RF suffix, in the RFQ.

Exact ordering string	Selection checkpoint	Inquiry
GLC-BX-D=	1 Gb/s BX10; Tx 1490 / Rx 1310 nm	Request a quote
GLC-BX-U=	1 Gb/s BX10; Tx 1310 / Rx 1490 nm	Request a quote
GLC-FE-100BX-D=	100 Mb/s BX10; Tx 1550 / Rx 1310 nm	Request a quote
GLC-GE-100FX=	100 Mb/s FX optic for supported Gigabit ports; multimode fiber	Request a quote
GLC-FE-100LX-RF	100 Mb/s LX10 family; verify Refresh provenance for the offered unit	Request a quote

Which D and U pair do I need?

The 1 Gb/s GLC-BX-D and GLC-BX-U use complementary wavelengths. The 100 Mb/s GLC-FE-100BX-D belongs to a different pair: its downstream wavelength is 1550 nm, not 1490 nm. Do not combine the two families merely because both names contain BX and D. Ask for the exact far-end module and operating speed. A complete bidirectional link also needs compatible fiber, connector condition and an optical budget.

Does GLC-GE-100FX make the fiber link Gigabit?

No. The GE host-side designation does not turn its 100BASE-FX optical link into a 1 Gb/s link. Check the exact host/port and software in the Cisco compatibility matrix. For LX, FX and BX, record the fiber type and connector arrangement separately; the family name alone does not approve a host combination.

What should a replacement quote include?

Provide quantity, both module labels, host and software, fiber type, length and measured loss, requested condition, delivery country and target date. Ask for readable labels, serial/lot evidence where available, and a test report appropriate to the link. Cisco listing an RF identifier does not certify a supplier batch. Price, lead time, available quantity, warranty and support eligibility require a current written offer.

Continue selection

• Cisco CWDM-SFP 1470–1610: Specify the Wavelength and Channel Plan

• Catalyst 9300 BOM: C9300L Uplinks, UB/UXB, HXN and RF Variants

Manufacturer references

• Cisco 100M Ethernet SFP data sheet

• Cisco SFP installation notes

• Cisco Refresh networking model list

• Cisco optics compatibility matrix

Reviewed 6 November 2026. Recheck host support and lifecycle status for the intended deployment. These guides do not assert stock or guaranteed compatibility.