HPE Synergy Virtual Connect 100Gb F32 Module enhancements
Forward Error Correction (FEC)
Forward error correction (FEC) is a digital signal processing technique used to correct errors and protect data integrity.
FireCode FEC
Reed-Solomon FEC
The HPE Virtual Connect 100Gb F32 Module supports RS-FEC for Ethernet ports only, which also works with Cisco and Arista. FEC is disabled for the FC ports and downlinks.
@100 G, FEC can be AUTO, None, or CL91/CL74.
@40 G, no FEC.
@25 G, FEC can be AUTO, None, or CL108/CL74.
@10 G, no FEC.
Expected behaviors for unsplit uplink ports
| Speed | FEC | Expected behavior |
|---|---|---|
| AUTO | AUTO | Copper DACs—AutoNeg and CL91 are enabled. SR4—No AutoNeg, FEC CL91 is enabled. LR4—No AutoNeg, no FEC. |
| AUTO | None | Copper DACs—AutoNeg is enabled, no FEC. SR4—No AutoNeg, no FEC. LR4—No AutoNeg, no FEC. |
| 100 G | AUTO/None
CL91/CL74 |
Fixed 100 G mode, no AutoNeg. In AUTO FEC mode, CL91 is enabled. |
| 40 G | None | Fixed 40 G mode, no AutoNeg.
FEC is not applicable to 40G speed. |
Expected behaviors for split uplink ports
| Speed | FEC | Expected behavior |
|---|---|---|
| AUTO | AUTO | Copper DACs—AutoNeg and CL108 are enabled. SR—No AutoNeg, FEC CL108 is enabled. LR—No AutoNeg, no FEC. |
| AUTO | None | Copper DACs—AutoNeg is enabled, no FEC. SR—No AutoNeg, no FEC. LR—No AutoNeg, no FEC. |
| 25 G | AUTO/None
CL108/CL74 |
Fixed 25 G mode, no AutoNeg. In AUTO FEC mode, CL108 is enabled. |
| 10 G | None | Fixed 10 G mode, no AutoNeg.
FEC is not applicable to 10 G speed. |
Expected link states when two devices are configured with different FEC configuration values
| FEC (Device 1) | FEC (Device 2) | Link state |
|---|---|---|
| AUTO | OFF | Down |
| OFF | OFF | Up |
| CL91 | CL91 | Up |
| CL91 | CL74 | Down |
| CL74 | CL74 | Up |
| CL108 | CL74 | Down |
| CL108 | CL108 | Up |
The FEC must match on both ends for the ports to link up.
The FEC is implemented at the PHY/MAC level. There is no way to know that "FEC mismatch" is causing the ports to not link up. Customers must pay attention to this configuration detail.
FEC introduces an ignorable amount of latency (a few ns).
For 100 G, CL91 (RS-FEC) is mandatory. Both link partners are expected to run the same mode. If the partner switch does not support CL91, set to NONE on HPE Synergy.
For both 25 G and 100 G speeds, FEC is recommended. Without FEC, the customer might see bit errors.