When attempting to establish a direct 10GbE connection between two HP ProLiant servers (DL580G5 and DL380G5) equipped with HP NC522SFP adapters using passive twinax cables, the link fails to initialize. This contrasts with successful connections when these same cables are used between servers and a Dell 5524 switch.

Passive SFP+ direct attach copper (DAC) cables are essentially fixed-length, point-to-point connections with these characteristics:

- Typically support distances up to 7m
- Lower power consumption than optical modules
- No autonegotiation capability
- Fixed as straight-through connections

Modern 10GbE implementations (including SFP+) generally incorporate auto-MDI/MDI-X functionality that automatically detects and corrects for straight-through vs. crossover requirements. However, there are exceptions:

• Some older NICs may not fully implement auto-MDI-X
• Certain SFP+ transceivers may have limitations
• Vendor-specific implementations might behave differently

Before considering cable replacements, try these diagnostic steps:

1. Verify SFP+ module compatibility:
   Get-HPnc522SFP -ListCompatibleModules
2. Check link state:
   netsh interface show interface
3. Test with different speed/duplex settings:
   Set-NetAdapterAdvancedProperty -Name "10GbE" -DisplayName "Speed & Duplex" -DisplayValue "10Gbps Full Duplex"

If direct DAC connection proves unreliable, consider these alternatives:

Option 1: Active Optical Cables

These provide better signal integrity and often more reliable auto-negotiation:

# Sample PowerShell to check supported module types
Get-NetAdapterHardwareInfo -Name "10GbE" | Select-Object SupportedTransceiverTypes

Option 2: Small 10GbE Switch

A compact switch can resolve connection issues while adding flexibility:

Recommended models:
- MikroTik CRS305-1G-4S+IN
- Ubiquiti USW-Flex-XG
- TP-Link T1700X-16TS

Option 3: Forced Link Settings

Some NICs allow manual configuration to force link establishment:

# Example for Intel NICs (may vary for HP)
Set-IntelNetAdapterSetting -Name "10GbE" -Property "ForceLink" -Value "Enabled"

When implementing multiple paths for iSCSI over 10GbE:

# MPIO configuration example
New-MSDSMSupportedHW -VendorId "HP" -ProductId "NC522SFP"
Set-MSDSMGlobalDefaultLoadBalancePolicy -Policy RR

When attempting to establish a direct 10GbE connection between two HP servers (DL580G5 and DL380G5) equipped with NC522SFP adapters using passive copper DAC cables, the link fails to initialize - despite these same cables working perfectly when connected through a Dell 5524 switch. This reveals a fundamental difference in how SFP+ ports handle direct device-to-device connections compared to traditional Ethernet.

SFP+ ports don't implement the same auto-MDI/MDIX functionality found in standard RJ45 Ethernet ports. The physical layer signaling requires proper alignment:

// Typical SFP+ port initialization sequence (simplified)
1. PHY detects cable insertion
2. Checks for signal integrity
3. Attempts link negotiation
4. Either establishes link or remains down

Three proven approaches work for direct SFP+ connections:

1. Active Optical Cables (AOC): Contain built-in signal processing to handle direct connections
2. Specialized DAC Configurations: Some vendors offer "crossover" DAC cables
3. Manual MDI Configuration: If supported by NIC firmware

For HP NC522SFP adapters, try forcing the link settings via PowerShell:

# Set NIC to full duplex 10G (replace "Ethernet 3" with your interface name)
Set-NetAdapterAdvancedProperty -Name "Ethernet 3" -DisplayName "Speed & Duplex" -DisplayValue "10 Gbps Full Duplex"

# Disable energy efficient Ethernet (may cause issues with direct connect)
Set-NetAdapterAdvancedProperty -Name "Ethernet 3" -DisplayName "Energy Efficient Ethernet" -DisplayValue "Disabled"

Based on field reports, these specific cables work for direct SFP+ connections:

• HP JG325A (3m active DAC)
• FS.com SFP-H10GB-CU3M (crossover variant)
• Cisco SFP-H10GB-CU3M (with modified EEPROM)

After physical connection, check link status in Windows:

# PowerShell command to verify link status
Get-NetAdapter | Where-Object {$_.InterfaceDescription -like "*NC522SFP*"} | Select Name, Status, LinkSpeed

For iSCSI multipath configurations, ensure proper MPIO policies are set in Windows Server 2012 to utilize multiple connections effectively.