S7-315-2PN Ethernet Ping Failure: Cable and NIC Diagnostics

Problem Statement and Symptoms

Symptom set observed when commissioning a SIMATIC S7-315-2 PN/DP (CPU order number 6ES7315-2EH14-0AB0) from an engineering PC over the integrated PROFINET interface:

• ping <PLC-IP> returns Destination host unreachable.
• ping 127.0.0.1 returns Destination host unreachable on the engineering PC (loopback reply failure is a strong indication that the link layer is down).
• ipconfig /all reports Media state: media disconnected when the patch cable is unplugged.
• Network adapter entry shows Description: Intel(R) Pro/1000 CT Network Connection and Physical Address 00-30-05-7C-7C-81 (OUI 00-30-05 is Intel's registered prefix per IEEE).
• Device Manager reports "This device is working properly." No yellow bangs.
• STEP 7 / TIA Portal online browse fails: Cannot reach partner or Connection to partner broken.

The TCP/IP stack is loaded (interface is bound), the driver is healthy, but the physical link never establishes. Field reports confirm this exact pattern when an Intel Pro/1000 CT NIC (controller family i82547) is connected to an S7-300 CPU with PROFINET interface using a straight-through patch cable, even though a different PC on the same engineering desk works fine on the same lead.

Affected Components and Versions

Reference documentation: SIMATIC S7-300 CPU 315-2 PN/DP manual (entry ID 12996906), Siemens S7-300 product page.

Root Cause #1: Cable Type Mismatch (Straight-Through vs Crossover)

The S7-315-2 PN/DP integrated switch and the Intel Pro/1000 CT NIC both advertise MDI/MDI-X capability, but in practice the older i82547 family on Windows XP exhibits Auto-MDI/MDIX behavior that does not always negotiate correctly against the S7-300 CPU port, particularly when:

• Auto-negotiation is disabled or fails on one side.
• The patch lead is wired straight-through (T568B on both ends) and the NIC's polarity correction does not swap pairs.
• The cable is longer than 80 m (Cat5e spec limit), but in bench rigs this is rarely the issue.

IEEE 802.3u (100BASE-TX) and 802.3ab (1000BASE-T) define Auto-Negotiation as the mechanism that selects link speed, duplex, and MDI/MDI-X state. When Auto-MDI/MDIX (Clause 40) fails, a crossover is required to align the TD+/- (pins 1,2) of one device with the RD+/- (pins 3,6) of the other.

Pinout Reference (T568A / T568B)

If swapping to a known-good crossover lead (or replacing the suspect straight lead with a crossover) restores link activity, root cause #1 is confirmed. The S7-300 CPU's PROFINET port LED will transition from off to steady green, and Device Manager on the PC will report link speed (typically 100 Mbit/s) under Network Connection Status > General > Speed.

Root Cause #2: Windows XP SP2 ICMP and Self-Ping Behavior

Windows XP SP2 introduced changes that affect the loopback ICMP path and the way ping reports unreachable local subnets:

• ICMP Echo handling. On SP1a, pinging the host's own IP with no link returns the destination's own echo reply (because the IP stack loopbacks). On SP2, ping to a host IP that has no link returns Destination host unreachable instead of an echo reply, because the routing subsystem reports the route as invalid when no link is detected.
• Windows Firewall default. SP2 enables Windows Firewall by default on every network interface. Inbound ICMP Echo Request is dropped silently. The result is Request timed out from a remote PC, even when the local stack is healthy.
• Route cache invalidation. When the link goes down, SP2 invalidates the local subnet route entry more aggressively than SP1a. Combined with the Intel driver exposing Media State: Media disconnected from the PHY, the result is the symptom set above.

Reference: Microsoft Knowledge Base article 330559 - TCP/IP behavior in Windows XP and the SP2 ICMP documentation issued with Service Pack 2 release notes.

Root Cause #3: NIC Driver and Media State Reporting

The i82547 family reports physical link state through NDIS 5.1 miniport drivers (e1000325.sys, e1q62x86.sys, PRO2KXP.sys) using the NDIS OID_GEN_MEDIA_CONNECT_STATUS OID. If the driver cannot establish a stable link (because of auto-negotiation failure with the S7-300 CPU port, or because the cable is mismatched), the OID reports NdisMediaStateDisconnected. The TCP/IP stack then exposes media disconnected via ipconfig /all.

Intel driver downloads and release notes are catalogued on Intel Ethernet driver support. For i82547EI specifically consult Intel ARK product page for i82547EI for the controller specification (10/100/1000BASE-T, PCI 2.3, Auto-MDI/MDIX supported per PHY datasheet, but driver behavior on XP SP2 may deviate from spec).

Diagnostic Procedure

1. Confirm the link LED on the S7-315-2 PN/DP X1 port. No LED indicates no physical link at the PHY. Steady green or flashing green/yellow indicates link up; record the color code from the CPU manual.
2. Capture ipconfig /all on the PC. Confirm DHCP/Static, IP, mask, gateway, and especially Media State and Description.
3. Validate the patch lead. Use a continuity tester or a managed switch's port diagnostics. Replace straight-through with crossover if connecting PC directly to CPU, or replace the suspect lead with a known-good Cat5e/Cat6 from stock.
4. Open Device Manager > Network Adapters > Intel Pro/1000 CT > Properties > Advanced. Confirm Speed & Duplex is set to Auto Negotiation. Hard-coding 100 Mbit/s Full Duplex is acceptable if Auto is unreliable.
5. Verify Windows Firewall state. netsh firewall show state on XP SP2. If enabled, allow ICMPv4 inbound explicitly as a diagnostic step.
6. Disable third-party security suites. Symantec, McAfee, Trend Micro host-based firewalls commonly block ICMP and ISO-on-TCP (port 102) used by STEP 7.
7. Reset the NIC. devcon restart "PCI\VEN_8086&DEV_1019" (VID 8086 = Intel, DID 1019 = 82547EI) or disable/enable from Device Manager.
8. Reload the i82547 driver. Uninstall, reboot, install latest WHQL-signed Intel driver for XP from the Intel Ethernet driver package.
9. Verify loopback. With a working cable, ping 127.0.0.1 must return four replies. If still failing, the NIC driver stack itself is corrupt - reinstall.
10. Verify host IP. ping <PC-IP> on the PC itself (self-ping). On XP SP2 with link up, expect four replies; with link down, expect Destination host unreachable (this is normal on SP2).
11. Verify CPU reachability. ping <S7-300-IP> from the PC. CPU default IP is 0.0.0.0 - assign via STEP 7 Hardware Config first.

Resolution Steps

1. Replace the patch lead. Use a Cat5e or Cat6 RJ45 lead. For a direct PC-to-CPU connection (no switch), use a crossover lead unless both devices demonstrably support Auto-MDI/MDIX.
2. Use the S7-300's integrated switch. Connect the PC to port X1 P1 and a second device (HMI, switch) to X1 P2. This guarantees one port is acting as MDI-X and removes the crossover requirement.
3. Assign a fixed IP to the CPU PROFINET interface. In STEP 7 V5.5 / TIA Portal, Hardware Configuration > CPU 315-2 PN/DP properties > PROFINET interface > Ethernet addresses. Example: 192.168.0.1 / 255.255.255.0; configure the PC in the same subnet, e.g. 192.168.0.10 / 255.255.255.0.
4. Disable Windows Firewall on the engineering PC as a controlled test, or create an inbound rule for ICMPv4 and TCP/102 (ISO-on-TCP) and UDP/34964 (PN-DCP). Re-enable after diagnostic.
5. Update the Intel driver. Use the latest Intel Ethernet Connection I340 / PRO/1000 driver package applicable to XP. Note that Intel officially retired support for the i82547 family on Windows 7+; XP remains the longest-supported client OS for the chip.
6. Disable energy-efficient Ethernet (EEE). The i82547 does not support 802.3az, but enabling EEE on a third-party partner device can cause link flapping. Set partner to EEE disabled if available.
7. Verify with STEP 7 / TIA Portal online. In TIA Portal V16+, Online > Accessible devices must list the CPU. In STEP 7 V5.5, PLC > Ethernet Editor > Browse should resolve the CPU.

Verification and Connectivity Testing

Successful commissioning is verified by completing the following checks in order:

1. Link LEDs on both PC NIC and CPU port X1 are steady green.
2. ipconfig /all reports Media State: Media connected and Speed: 100.0 Mbps.
3. ping 127.0.0.1 from PC returns four replies, <1 ms.
4. ping <PC-IP> from PC returns four replies.
5. ping <CPU-IP> from PC returns four replies, typically <1 ms on a directly connected link.
6. ping <PC-IP> from CPU web interface (open browser to http://<CPU-IP>) shows reachable host in diagnostic page; the CPU web server (firmware >= V3.2) must display module information.
7. STEP 7 / TIA Portal Online > Accessible Devices lists the CPU MAC address and assigned IP.
8. CPU diagnostic buffer no longer contains Communication error or No station found entries.

If any step fails, return to the diagnostic procedure above and isolate the failing layer.

Firmware, Driver, and Compatibility Matrix

Modern Replacement Considerations

When the Windows XP SP2 engineering PC is decommissioned, plan the migration in three layers:

1. Hardware. Replace the i82547-based NIC with an Intel I210 / I211 / I219 or a Realtek RTL8111H. These parts implement robust Auto-MDI/MDIX and are validated against the S7-300 PROFINET port at 100 Mbit/s full duplex.
2. Software. Move from STEP 7 V5.5 + XP SP2 to TIA Portal V18 on Windows 10 LTSC 2021 (or Windows 11 LTSC). STEP 7 V5.5 SP4 is the last release with official Windows XP support.
3. Network topology. Use a managed industrial switch (SCALANCE XC-100, XC-200) between the PC and the CPU. This isolates PC NIC behavior from CPU port behavior and gives you port diagnostics, LLDP, and PROFINET DCP integration.

Reference for SCALANCE switches: Siemens SCALANCE XC-100/XC-200 operating instructions (entry ID 109751484). Reference for PROFINET cabling and connector pinout: PROFINET Installation Guide (entry ID 27069465).

Frequently Asked Questions (FAQ)