diff --git a/sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.c b/sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.c
index b8dc68d0bbadef36cda13c834e7366169686fc27..c4ecf556bc4388a5e092c22ba4718df160e0e660 100644
--- a/sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.c
+++ b/sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.c
@@ -460,17 +460,10 @@ bool _is_reachable(_nib_onl_entry_t *entry)
static inline uint32_t _exp_backoff_retrans_timer(uint8_t ns_sent,
uint32_t retrans_timer)
{
- uint32_t tmp = random_uint32_range(NDP_MIN_RANDOM_FACTOR,
- NDP_MAX_RANDOM_FACTOR);
-
- /* backoff according to https://tools.ietf.org/html/rfc7048 with
- * BACKOFF_MULTIPLE == 2 */
- tmp = ((1 << ns_sent) * retrans_timer * tmp) / US_PER_MS;
- /* random factors were statically multiplied with 1000 ^ */
- if (tmp > NDP_MAX_RETRANS_TIMER_MS) {
- tmp = NDP_MAX_RETRANS_TIMER_MS;
- }
- return tmp;
+ uint32_t factor = random_uint32_range(NDP_MIN_RANDOM_FACTOR,
+ NDP_MAX_RANDOM_FACTOR);
+
+ return _exp_backoff_retrans_timer_factor(ns_sent, retrans_timer, factor);
}
#if GNRC_IPV6_NIB_CONF_REDIRECT
diff --git a/sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.h b/sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.h
index abfdb8f263cb8a0374b3a6e944b6c95d74ca26fe..aa7210992b2516dbf0ff690d32ee413525130322 100644
--- a/sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.h
+++ b/sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.h
@@ -81,6 +81,43 @@ void _snd_uc_ns(_nib_onl_entry_t *nbr, bool reset);
void _handle_sl2ao(gnrc_netif_t *netif, const ipv6_hdr_t *ipv6,
const icmpv6_hdr_t *icmpv6, const ndp_opt_t *sl2ao);
+/**
+ * @brief Calculates truncated exponential back-off for retransmission timer
+ * for neighbor solicitations based on a randomized factor
+ *
+ * The truncation is at @ref NDP_MAX_RETRANS_TIMER_MS. as suggested in
+ * [RFC 7048, section 3](https://tools.ietf.org/html/rfc7048#section-3).
+ *
+ * @param[in] ns_sent Neighbor solicitations sent up until now. Must be
+ * lesser than or equal to @ref NDP_MAX_NS_NUMOF.
+ * @param[in] retrans_timer Currently configured retransmission timer in ms.
+ * @param[in] factor An equally distributed factor between
+ * @ref NDP_MIN_RANDOM_FACTOR and (exclusive)
+ * @ref NDP_MAX_RANDOM_FACTOR.
+ *
+ * @pre (NDP_MIN_RANDOM_FACTOR <= factor < NDP_MAX_RANDOM_FACTOR)
+ * @pre (ns_sent <= NDP_MAX_NS_NUMOF)
+ *
+ * @return exponential back-off of the retransmission timer
+ */
+static inline uint32_t _exp_backoff_retrans_timer_factor(uint8_t ns_sent,
+ uint32_t retrans_timer,
+ uint32_t factor)
+{
+ assert(NDP_MIN_RANDOM_FACTOR <= factor);
+ assert(factor < NDP_MAX_RANDOM_FACTOR);
+ assert(ns_sent <= NDP_MAX_NS_NUMOF);
+ /* backoff according to https://tools.ietf.org/html/rfc7048 with
+ * BACKOFF_MULTIPLE == 2 */
+ uint32_t res = (uint32_t)(((uint64_t)(((uint32_t) 1) << ns_sent) *
+ retrans_timer * factor) / US_PER_MS);
+ /* random factors were statically multiplied with 1000 */
+ if (res > NDP_MAX_RETRANS_TIMER_MS) {
+ res = NDP_MAX_RETRANS_TIMER_MS;
+ }
+ return res;
+}
+
#if GNRC_IPV6_NIB_CONF_ARSM || defined(DOXYGEN)
/**
* @brief Handler for @ref GNRC_IPV6_NIB_SND_UC_NS and
diff --git a/tests/unittests/tests-gnrc_ipv6_nib/tests-gnrc_ipv6_nib-internal.c b/tests/unittests/tests-gnrc_ipv6_nib/tests-gnrc_ipv6_nib-internal.c
index be6e75d6836e93e59dccd54230cbf138f3a45d1d..a171d3c2a173ba3eb5afd42436c5912af0f342d5 100644
--- a/tests/unittests/tests-gnrc_ipv6_nib/tests-gnrc_ipv6_nib-internal.c
+++ b/tests/unittests/tests-gnrc_ipv6_nib/tests-gnrc_ipv6_nib-internal.c
@@ -21,6 +21,7 @@
#include "net/gnrc/ipv6/nib.h"
#include "_nib-internal.h"
+#include "_nib-arsm.h"
#include "unittests-constants.h"
@@ -1947,6 +1948,58 @@ static void test_nib_abr_iter__three_elem_middle_removed(void)
}
#endif
+static void test_retrans_exp_backoff(void)
+{
+ TEST_ASSERT_EQUAL_INT(0,
+ _exp_backoff_retrans_timer_factor(0, 0, NDP_MIN_RANDOM_FACTOR));
+ /* factor 1000 means multiplied by 1 */
+ TEST_ASSERT_EQUAL_INT(NDP_RETRANS_TIMER_MS,
+ _exp_backoff_retrans_timer_factor(0, NDP_RETRANS_TIMER_MS, 1000));
+ TEST_ASSERT_EQUAL_INT(2 * NDP_RETRANS_TIMER_MS, /* 2^1 = 2 */
+ _exp_backoff_retrans_timer_factor(1, NDP_RETRANS_TIMER_MS, 1000));
+ TEST_ASSERT_EQUAL_INT(4 * NDP_RETRANS_TIMER_MS, /* 2^2 = 4 */
+ _exp_backoff_retrans_timer_factor(2, NDP_RETRANS_TIMER_MS, 1000));
+ TEST_ASSERT_EQUAL_INT(8 * NDP_RETRANS_TIMER_MS, /* 2^3 = 8 */
+ _exp_backoff_retrans_timer_factor(3, NDP_RETRANS_TIMER_MS, 1000));
+ TEST_ASSERT_EQUAL_INT(16 * NDP_RETRANS_TIMER_MS, /* 2^4 = 16 */
+ _exp_backoff_retrans_timer_factor(4, NDP_RETRANS_TIMER_MS, 1000));
+ TEST_ASSERT_EQUAL_INT(32 * NDP_RETRANS_TIMER_MS, /* 2^5 = 32 */
+ _exp_backoff_retrans_timer_factor(5, NDP_RETRANS_TIMER_MS, 1000));
+ TEST_ASSERT_EQUAL_INT(NDP_MAX_RETRANS_TIMER_MS,
+ _exp_backoff_retrans_timer_factor(6, NDP_RETRANS_TIMER_MS, 1000));
+ TEST_ASSERT_EQUAL_INT(NDP_MAX_RETRANS_TIMER_MS,
+ _exp_backoff_retrans_timer_factor(0, UINT32_MAX,
+ NDP_MIN_RANDOM_FACTOR));
+ TEST_ASSERT_EQUAL_INT(NDP_MAX_RETRANS_TIMER_MS,
+ _exp_backoff_retrans_timer_factor(0, UINT32_MAX,
+ NDP_MAX_RANDOM_FACTOR - 1));
+ TEST_ASSERT_EQUAL_INT(NDP_MAX_RETRANS_TIMER_MS,
+ _exp_backoff_retrans_timer_factor(NDP_MAX_NS_NUMOF, UINT32_MAX,
+ NDP_MAX_RANDOM_FACTOR - 1));
+ TEST_ASSERT_EQUAL_INT(NDP_MAX_RETRANS_TIMER_MS,
+ _exp_backoff_retrans_timer_factor(NDP_MAX_NS_NUMOF,
+ NDP_RETRANS_TIMER_MS,
+ NDP_MAX_RANDOM_FACTOR - 1));
+ TEST_ASSERT_EQUAL_INT(NDP_MAX_RETRANS_TIMER_MS,
+ _exp_backoff_retrans_timer_factor(NDP_MAX_NS_NUMOF,
+ NDP_RETRANS_TIMER_MS,
+ NDP_MIN_RANDOM_FACTOR));
+ TEST_ASSERT_EQUAL_INT(NDP_MAX_RETRANS_TIMER_MS,
+ _exp_backoff_retrans_timer_factor(NDP_MAX_NS_NUMOF,
+ NDP_MAX_RETRANS_TIMER_MS,
+ NDP_MAX_RANDOM_FACTOR - 1));
+ TEST_ASSERT_EQUAL_INT(32768,
+ _exp_backoff_retrans_timer_factor(NDP_MAX_NS_NUMOF - 1, 1,
+ NDP_MIN_RANDOM_FACTOR));
+ TEST_ASSERT_EQUAL_INT(47653,
+ _exp_backoff_retrans_timer_factor(5U, 1118U, 1332));
+ TEST_ASSERT_EQUAL_INT(47653,
+ _exp_backoff_retrans_timer_factor(5U, 1118U, 1332));
+ /* test 64-bit overfrow */
+ TEST_ASSERT_EQUAL_INT(NDP_MAX_RETRANS_TIMER_MS,
+ _exp_backoff_retrans_timer_factor(NDP_MAX_NS_NUMOF, 32768, 1024));
+}
+
Test *tests_gnrc_ipv6_nib_internal_tests(void)
{
EMB_UNIT_TESTFIXTURES(fixtures) {
@@ -2046,6 +2099,7 @@ Test *tests_gnrc_ipv6_nib_internal_tests(void)
new_TestFixture(test_nib_abr_iter__three_elem),
new_TestFixture(test_nib_abr_iter__three_elem_middle_removed),
#endif
+ new_TestFixture(test_retrans_exp_backoff),
};
EMB_UNIT_TESTCALLER(tests, set_up, NULL,