diff --git a/eth.cpp b/eth.cpp
new file mode 100644
index 0000000..32dbe89
--- /dev/null
+++ b/eth.cpp
@@ -0,0 +1,103 @@
+/*
+ * Copyright 2018 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "eth.hpp"
+
+#include "main.hpp"
+
+#include <cstdint>
+#include <string>
+
+namespace google
+{
+namespace ipmi
+{
+
+struct EthDeviceRequest
+{
+    uint8_t subcommand;
+} __attribute__((packed));
+
+// The reply to the ethdevice command specifies the
+// IPMI channel number and the if_name used for the
+// ncis connection.
+struct EthDeviceReply
+{
+    uint8_t subcommand;
+    uint8_t channel;
+    // if_name_len doesn't include the null-terminator.
+    uint8_t if_name_len;
+    uint8_t if_name[0];
+} __attribute__((packed));
+
+// The phosphor-host-ipmi daemon requires a configuration that maps
+// the if_name to the IPMI LAN channel.  However, that doesn't strictly
+// define which is meant to be used for NCSI.
+#ifndef NCSI_IPMI_CHANNEL
+#define NCSI_IPMI_CHANNEL 1
+#endif
+
+#ifndef NCSI_IF_NAME
+#define NCSI_IF_NAME eth0
+#endif
+
+// TOOD(venture): The ipmid.h has this macro, which is a header we
+// can't normally access.
+#ifndef MAX_IPMI_BUFFER
+#define MAX_IPMI_BUFFER 64
+#endif
+
+// To deal with receiving a string without quotes.
+#define QUOTE(name) #name
+#define STR(macro) QUOTE(macro)
+#define NCSI_IF_NAME_STR STR(NCSI_IF_NAME)
+
+ipmi_ret_t GetEthDevice(const uint8_t* reqBuf, uint8_t* replyBuf,
+                        size_t* dataLen)
+{
+    if ((*dataLen) < sizeof(struct EthDeviceRequest))
+    {
+        fprintf(stderr, "Invalid command length: %lu\n", (*dataLen));
+        return IPMI_CC_INVALID;
+    }
+
+    std::string device = NCSI_IF_NAME_STR;
+    if (device.length() == 0)
+    {
+        fprintf(stderr, "Invalid eth string\n");
+        return IPMI_CC_INVALID;
+    }
+
+    if ((sizeof(struct EthDeviceReply) + device.length()) > MAX_IPMI_BUFFER)
+    {
+        fprintf(stderr, "Response would overflow response buffer\n");
+        return IPMI_CC_INVALID;
+    }
+
+    // Fill in the response buffer.
+    auto reply = reinterpret_cast<struct EthDeviceReply*>(&replyBuf[0]);
+    reply->subcommand = SysGetEthDevice;
+    reply->channel = NCSI_IPMI_CHANNEL;
+    reply->if_name_len = device.length();
+    memcpy(reply->if_name, device.c_str(), device.length());
+
+    (*dataLen) = sizeof(struct EthDeviceReply) + device.length();
+
+    return IPMI_CC_OK;
+}
+
+} // namespace ipmi
+} // namespace google