diff --git a/tools/testing/selftests/net/forwarding/router.sh b/tools/testing/selftests/net/forwarding/router.sh
index 057f91b05098..b98ea9449b8b 100755
--- a/tools/testing/selftests/net/forwarding/router.sh
+++ b/tools/testing/selftests/net/forwarding/router.sh
@@ -1,6 +1,24 @@
 #!/bin/bash
 # SPDX-License-Identifier: GPL-2.0
 
+# +--------------------+                     +----------------------+
+# | H1                 |                     |                   H2 |
+# |                    |                     |                      |
+# |              $h1 + |                     | + $h2                |
+# |     192.0.2.2/24 | |                     | | 198.51.100.2/24    |
+# | 2001:db8:1::2/64 | |                     | | 2001:db8:2::2/64   |
+# |                  | |                     | |                    |
+# +------------------|-+                     +-|--------------------+
+#                    |                         |
+# +------------------|-------------------------|--------------------+
+# | SW               |                         |                    |
+# |                  |                         |                    |
+# |             $rp1 +                         + $rp2               |
+# |     192.0.2.1/24                             198.51.100.1/24    |
+# | 2001:db8:1::1/64                             2001:db8:2::1/64   |
+# |                                                                 |
+# +-----------------------------------------------------------------+
+
 ALL_TESTS="
 	ping_ipv4
 	ping_ipv6