From b4e536f371a53dd8b25d2d454d029fecf8c955de Mon Sep 17 00:00:00 2001
From: dmiller <dmiller@e0a8ed71-7df4-0310-8962-fdc924857419>
Date: Wed, 3 Sep 2025 17:04:48 +0000
Subject: [PATCH] Only use eth handle for Ethernet on non-Windows systems.

---
 libnetutil/netutil.cc | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/libnetutil/netutil.cc b/libnetutil/netutil.cc
index 166582568..e7d0783d7 100644
--- a/libnetutil/netutil.cc
+++ b/libnetutil/netutil.cc
@@ -1019,7 +1019,20 @@ netutil_eth_t *netutil_eth_open(const char *device) {
   } while (0);
 #else
   eth_handle(e) = eth_open(device);
-  e->datalink = DLT_EN10MB;
+  if (eth_handle(e)) {
+    eth_addr_t ea;
+    /* No guarantees this is Ethernet. Dnet doesn't offer a way to check the L2
+     * protocol, so we'll try to get the Ethernet address to confirm.
+     */
+    if (0 == eth_get(eth_handle(e), &ea) && 0 != memcmp(&ea, "\0\0\0\0\0\0", 6)) {
+      e->datalink = DLT_EN10MB;
+    }
+    else {
+      // Not a data link we know about.
+      eth_handle_close(eth_handle(e));
+      eth_handle(e) = NULL;
+    }
+  }
 #endif
 
   if (eth_handle(e) == NULL) {