SFP LR vs SR: Choosing the Right Cisco 10G Transceiver
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The short answer
SFP LR vs SR comes down to the fiber you have and how far the link has to go. Choose SR for multimode fiber, up to about 300 m on OM3 or 400 m on OM4. Choose LR for single-mode fiber, up to 10 km. Both run at 10 Gbps. What differs is the light source, the fiber type and the reach.
In Cisco terms, that means the SFP-10G-SR-S for short runs inside a building and the SFP-10G-LR-S for longer runs. For most campus closets and internal runs, SR is the cheaper choice. Between buildings, SR often can’t reach, so LR is the safer option.
Quick comparison
|
Type |
Fiber |
Wavelength |
Typical reach |
Typical use |
Cisco part |
|---|---|---|---|---|---|
|
SR |
Multimode |
850 nm |
Up to 300 m (OM3) or 400 m (OM4) |
Inside a building |
SFP-10G-SR-S |
|
LR |
Single-mode |
1310 nm |
Up to 10 km |
Between buildings |
SFP-10G-LR-S |
What SR and LR actually mean
SR stands for short reach and LR for long reach. Each follows an IEEE 10 Gigabit Ethernet standard tied to a specific fiber type.
An SR optic uses an 850 nm laser on multimode fiber. An LR optic uses a 1310 nm laser on single-mode fiber. They can’t talk to each other, even though both use the same LC duplex connector and SFP+ port.
SR: multimode fiber over short distances
The Cisco SFP-10G-SR-S is the usual choice for runs inside a building or between nearby rooms. Its reach depends on the grade of multimode fiber installed:
|
Fiber type |
Typical color |
Approximate SR reach |
|---|---|---|
|
OM1 |
Orange |
26 to 33 m |
|
OM2 |
Orange |
82 m |
|
OM3 |
Aqua |
300 m |
|
OM4 |
Aqua or violet |
400 m |
Older fiber (OM1 and OM2) cuts the reach sharply, so check the grade before you order.
LR: single-mode fiber over long distances
The Cisco SFP-10G-LR-S reaches up to 10 km over standard single-mode fiber (OS2, usually yellow-jacketed). Distance isn’t the main reason to choose it. If the fiber between your buildings is single-mode, LR is simply the optic that matches it. LR also works fine on short single-mode runs, so a 50-meter link on yellow fiber still uses LR.
Which one fits your network
Start with the fiber, not the optic. Check the jacket color and printing on the cable, or look at your cabling records. Then match the distance:
- Multimode, under 300 m: SR.
- Multimode, 300 to 400 m: SR only if the fiber is OM4.
- Single-mode, any distance up to 10 km: LR.
- Single-mode, 10 to 40 km: ER.
- Single-mode, up to 80 km: ZR.
If you are not sure what is in the wall, test or trace it first. Guessing costs more than checking.
Inside one building or server room
Usually SR. Over OM3 or OM4 multimode fiber, the SFP-10G-SR-S covers most closet-to-closet and server room links at the lowest cost. SR optics generally cost less than LR, and multimode patch cords are cheaper too.
Between buildings on a school campus or agency site
Usually LR, if single-mode fiber is installed. The SFP-10G-LR-S matches a link across a campus. If you are cabling a new run between buildings, single-mode costs a little more up front but leaves room to move to faster speeds later without pulling new cable.
When you need even longer reach
Beyond 10 km, Cisco’s options are ER (extended reach, about 40 km) and ZR (about 80 km). Both use 1550 nm lasers over single-mode fiber. You may also see “ZX” on some optics. Cisco uses that label on gigabit parts, and some third-party makers use it for 80 km 10G optics. For Cisco 10G, search for ER and ZR. On very short single-mode runs, ER and ZR optics can overload the receiver and may need an inline attenuator, so check the data sheet for the exact part before ordering. You can browse our Cisco transceiver modules to compare reach classes, or ask us for a quote on long-reach parts.
Will it work with your Cisco switch?
In most cases, yes, as long as the switch has an SFP+ port and runs software recent enough to recognize the module. The SFP-10G-SR-S and SFP-10G-LR-S are used in many Catalyst switches, but support depends on the exact model and software release. Check Cisco’s Transceiver Module Group (TMG) compatibility matrix before you order.
Check the switch model and port type
Two quick checks prevent most problems. First, confirm the port is SFP+ and not plain SFP, because a 1G-only port can’t run a 10G optic. Second, make sure your software version meets the minimum for that module. Our SFP compatibility guide explains how to read the matrix.
What the “-S” in SFP-10G-SR-S and SFP-10G-LR-S means
The “-S” marks Cisco’s S-Class optics. They use the same wavelength, fiber type and reach as the non-S versions, but they carry Ethernet traffic only. The non-S versions also support extra protocols, such as OTN and WAN-PHY, that most office and campus networks never use. S-Class parts usually cost less.
For a normal Ethernet link between two switches, the S-Class part is enough as long as your switch supports it. If the link goes to a storage switch or a carrier network, check the data sheet first.
Cabling mistakes that cause link problems
Most “bad optic” tickets turn out to be cabling. Common examples:
- Wrong fiber for the optic. An SR optic on single-mode fiber, or an LR optic on multimode, will not link. Check the jacket color on both the trunk and the patch cords.
- Mismatched ends. Both ends of a link must use the same type: SR to SR, LR to LR.
- Assuming OM3 distances on older fiber. If the fiber is OM1 or OM2, the 300-meter figure does not apply.
- Dirty connectors. A speck of dust on an LC ferrule can drop a link or cause errors. Clean before you plug in.
- Swapped transmit and receive. If you have a duplex pair and the link stays down, try flipping the pair at one end.
- Sharp bends. Kinked patch cords cause loss, so keep gentle curves.
Our transceiver speed and distance guide has a broader chart if you are comparing 1G, 10G and faster options.
Common questions
What is the difference between SFP LR and SR?
SR uses 850 nm light across multimode fiber for short runs, reaching about 400 m on the highest grade. LR uses 1310 nm light on single-mode fiber and reaches 10 km. They can’t be swapped on the same link.
What is the difference between multimode and single-mode SFP?
Multimode optics send light through a wider fiber core and suit shorter distances. Single-mode optics send a tighter beam through a narrower core and travel much farther. Your installed fiber decides which type you need.
How far does SFP-10G-LR reach?
Up to 10 kilometers over standard single-mode fiber. Actual reach depends on connector quality and splice loss along the path.
Is SFP-10G-SR-S compatible with my switch?
It works with many Cisco Catalyst switches that have SFP+ ports, though support varies by model and software. Check the Cisco compatibility matrix for your specific switch.
What is the difference between SFP-10G-LR-S and SFP-10G-LR?
The “-S” marks the S-Class version. Speed and reach are the same, but S-Class runs Ethernet only, while the non-S part also supports extra protocols that most office and campus networks do not use. S-Class usually costs less.
Can I use an SR optic on one end and an LR optic on the other?
No. The two ends use different wavelengths and fiber types, so the link will not come up.
How many do I need for one link?
Two, one at each end, and both must be the same type.
Get a quote for bulk orders
Buying for a district, campus or agency? Send us the switch models, fiber type and link distances, and we will help match the right optics and quantities. We are an authorized reseller, and our orders come with the seller’s warranty. When you are ready, request a quote and we will send pricing for your PO.