diff --git a/eth.hpp b/eth.hpp
index fbd06ca..60a98b5 100644
--- a/eth.hpp
+++ b/eth.hpp
@@ -7,6 +7,18 @@
 namespace ipmi
 {
 
+// 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));
+
 // Handle the eth query command.
 // Sys can query the if_name and IPMI channel of the BMC's NCSI ethernet
 // device.