Limitations on Configuring a Forced Speed on VMware SD-WAN Edge Models 520, 540, 620, 640, 680, 3400, 3800, and 3810

Products

• VMware SD-WAN by VeloCloud

Issue/Introduction

Symptoms:

A user disables autonegotiation to hardcode speed and duplex on ports GE1 - GE4 on a VMware SD-WAN Edge model 620, 640 or 680; on ports GE3 or GE4 on an Edge 3400, 3800, or 3810; or on an Edge 520/540 when an SFP with a copper interface is used on ports SFP1 or SFP2, and finds that even after a reboot the link does not come up.

Note: For any change that disables DPDK on an interface, such as hardcoding speed and duplex, a reboot of the Edge may be needed to bring the port up.

An example of this issue: a user configures GE3 on an Edge 640 to turn off autonegotiation and forces a speed of 100 Mbps and Full Duplex. When the user goes to Remote Diagnostics > Interface Status > Routed Interfaces, they would observe that the GE3 link is showing as not detected.

Environment

VMware SD-WAN by VeloCloud

Cause

The Edge Models 520, 540, 620, 640, 680, 3400, 3800, and 3810 all use the Intel Ethernet Controller i350, which has a limitation that when autonegotiation is not used on both sides of the link, it is not able to dynamically detect the appropriate wires to transmit and receive on (auto-MDIX). If both sides of the connection are transmitting and receiving on the same wires, the link will not be detected.

The affected models and ports are:

• Edge models 520 and 540: ports SFP1 and SFP2 are controlled by the i350 Ethernet Controller, so when a copper SFP is used this issue may occur.
• Edge models 620, 640, and 680: ports GE1 - GE4 are controlled by the i350 Ethernet Controller.
• Edge models 3400, 3800, and 3810: ports GE3 and GE4 are controlled by the i350 Ethernet Controller.

Resolution

This problem is due to Intel's Ethernet controller and Intel will not alter it to support MDIX. For that reason we recommend the steps in the Workaround section for ways to remediate this limitation.

Workaround:
If the peer side also does not support auto-MDIX without autonegotiation, and the link does not come up with a straight cable, then a crossover Ethernet cable will be needed to bring the link up.

Additional Information

Impact/Risks:

The link does not come up on the affected port and no traffic will pass.