gnrc/ipv6/nib: allow for predictable static link-local addresses

examples/gnrc_networking/Makefile

@@ -54,7 +54,7 @@ endif
 # this might be useful for testing, in cases where you cannot or do not want to
 # run a shell with ifconfig to get the real link lokal address.
 #IPV6_STATIC_LLADDR ?= '"fe80::cafe:cafe:cafe:1"'
-#CFLAGS += -DGNRC_IPV6_STATIC_LLADDR=$(IPV6_STATIC_LLADDR)
+#CFLAGS += -DCONFIG_GNRC_IPV6_STATIC_LLADDR=$(IPV6_STATIC_LLADDR)
 
 # Uncomment this to join RPL DODAGs even if DIOs do not contain
 # DODAG Configuration Options (see the doc for more info)

examples/gnrc_networking_mac/Makefile

@@ -49,7 +49,7 @@ DEVELHELP ?= 1
 # this might be useful for testing, in cases where you cannot or do not want to
 # run a shell with ifconfig to get the real link lokal address.
 #IPV6_STATIC_LLADDR ?= '"fe80::cafe:cafe:cafe:1"'
-#CFLAGS += -DGNRC_IPV6_STATIC_LLADDR=$(IPV6_STATIC_LLADDR)
+#CFLAGS += -DCONFIG_GNRC_IPV6_STATIC_LLADDR=$(IPV6_STATIC_LLADDR)
 
 # Uncomment this to join RPL DODAGs even if DIOs do not contain
 # DODAG Configuration Options (see the doc for more info)

sys/include/net/gnrc/ipv6.h

@@ -157,19 +157,30 @@ extern "C" {
  * This macro allows to specify a certain link local IPv6 address to be assigned
  * to a network interface on startup, which might be handy for testing.
  * Note: a) a interface will keep its auto-generated link local address, too
- *       b) the address is incremented by 1, if multiple interfaces are present
+ *       b) the address is incremented by the interface PID unless
+            `CONFIG_GNRC_IPV6_STATIC_LLADDR_IS_FIXED` is set.
  *
  * To use the macro just add it to `CFLAGS` in the application's Makefile, like:
  *
  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ {.mk}
  * IPV6_STATIC_LLADDR ?= '"fe80::cafe:cafe:cafe:1"'
- * CFLAGS += -DGNRC_IPV6_STATIC_LLADDR=$(STATIC_IPV6_LLADDR)
+ * CFLAGS += -DCONFIG_GNRC_IPV6_STATIC_LLADDR=$(STATIC_IPV6_LLADDR)
  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  */
-#define GNRC_IPV6_STATIC_LLADDR
+#define CONFIG_GNRC_IPV6_STATIC_LLADDR
 #endif /* DOXYGEN */
 /** @} */
 
+/**
+ * @brief   Use the same static IPv6 link local address on every network interface
+ *
+ * When CONFIG_GNRC_IPV6_STATIC_LLADDR is used, to not add the interface pid to the
+ * set static address but use the same static link local address for all interfaces.
+ */
+#ifndef CONFIG_GNRC_IPV6_STATIC_LLADDR_IS_FIXED
+#define CONFIG_GNRC_IPV6_STATIC_LLADDR_IS_FIXED 0
+#endif
+
 /**
  * @brief Message queue size to use for the IPv6 thread.
  */

sys/net/gnrc/network_layer/ipv6/Kconfig

@@ -22,6 +22,29 @@ config GNRC_IPV6_MSG_QUEUE_SIZE_EXP
         represents the exponent of 2^n, which will be used as the size of
         the queue.
 
+config GNRC_IPV6_STATIC_LLADDR_ENABLE
+    bool "Add a static IPv6 link local address to any network interface"
+    help
+         This allows to specify a certain link local IPv6 address to be assigned
+         to a network interface on startup, which might be handy for testing.
+
+         A interface will keep its auto-generated link local address, too.
+
+config GNRC_IPV6_STATIC_LLADDR
+    string "Static link-local address"
+    depends on GNRC_IPV6_STATIC_LLADDR_ENABLE
+    default "fe80::cafe:cafe:cafe:1"
+    help
+         The address is configured on each interface and incremented by the
+         interface PID.
+
+config GNRC_IPV6_STATIC_LLADDR_IS_FIXED
+    bool "Same link-local address on every interface"
+    depends on GNRC_IPV6_STATIC_LLADDR_ENABLE
+    help
+         Don't add the interface PID to the least significant byte
+         of the address.
+
 endif # KCONFIG_USEMODULE_GNRC_IPV6
 
 rsource "blacklist/Kconfig"

sys/net/gnrc/network_layer/ipv6/nib/nib.c

@@ -115,16 +115,18 @@
 
 static void _add_static_lladdr(gnrc_netif_t *netif)
 {
-#ifdef GNRC_IPV6_STATIC_LLADDR
+#ifdef CONFIG_GNRC_IPV6_STATIC_LLADDR
     /* parse addr from string and explicitly set a link local prefix
      * if ifnum > 1 each interface will get its own link local address
-     * with GNRC_IPV6_STATIC_LLADDR + i
+     * with CONFIG_GNRC_IPV6_STATIC_LLADDR + i
      */
-    char lladdr_str[] = GNRC_IPV6_STATIC_LLADDR;
+    const char lladdr_str[] = CONFIG_GNRC_IPV6_STATIC_LLADDR;
     ipv6_addr_t lladdr;
 
     if (ipv6_addr_from_str(&lladdr, lladdr_str) != NULL) {
-        lladdr.u8[15] += netif->pid;
+        if (!IS_ACTIVE(CONFIG_GNRC_IPV6_STATIC_LLADDR_IS_FIXED)) {
+            lladdr.u8[15] += netif->pid;
+        }
         assert(ipv6_addr_is_link_local(&lladdr));
         gnrc_netif_ipv6_addr_add_internal(
                 netif, &lladdr, 64U, GNRC_NETIF_IPV6_ADDRS_FLAGS_STATE_VALID
@@ -525,7 +527,7 @@
          icmpv6_len -= (opt->len << 3), \
          opt = (ndp_opt_t *)(((uint8_t *)opt) + (opt->len << 3)))
 
 #if IS_ACTIVE(CONFIG_GNRC_IPV6_NIB_ROUTER)
 static void _handle_rtr_sol(gnrc_netif_t *netif, const ipv6_hdr_t *ipv6,
                             const ndp_rtr_sol_t *rtr_sol, size_t icmpv6_len)
 {