From cc0101472e7f7eafb973898c3a5f2f5b27b8e512 Mon Sep 17 00:00:00 2001
From: Oleg Hahm <oleg@hobbykeller.org>
Date: Thu, 24 Sep 2015 17:06:51 +0200
Subject: [PATCH] 6lowpan: do garbage collect unreachable NCEs
RFC6775 says "if NUD on the router determines that the host is UNREACHABLE (based on the logic in [RFC4861]), the NCE SHOULD NOT be deleted but rather retained until the Registration Lifetime expires." Since this is a "SHOULD NOT" and not a "MUST NOT", we can still remove these NCEs to circumvent NCEs going into UNREACHABLE and never leave this state again. Actually removing these entries from the cache seems also be the better choice for memory constraint device.
---
sys/net/gnrc/network_layer/ndp/gnrc_ndp.c | 24 +++++++++++------------
1 file changed, 11 insertions(+), 13 deletions(-)
diff --git a/sys/net/gnrc/network_layer/ndp/gnrc_ndp.c b/sys/net/gnrc/network_layer/ndp/gnrc_ndp.c
index b565e6683a..adf1eb8b40 100644
--- a/sys/net/gnrc/network_layer/ndp/gnrc_ndp.c
+++ b/sys/net/gnrc/network_layer/ndp/gnrc_ndp.c
@@ -678,19 +678,17 @@ void gnrc_ndp_retrans_nbr_sol(gnrc_ipv6_nc_t *nc_entry)
}
}
else if (nc_entry->probes_remaining <= 1) {
-#ifdef MODULE_GNRC_SIXLOWPAN_ND_ROUTER
- if (nc_entry->iface != KERNEL_PID_UNDEF) {
- gnrc_ipv6_netif_t *ipv6_iface = gnrc_ipv6_netif_get(nc_entry->iface);
- if ((ipv6_iface->flags & GNRC_IPV6_NETIF_FLAGS_SIXLOWPAN) &&
- (ipv6_iface->flags & GNRC_IPV6_NETIF_FLAGS_ROUTER) &&
- (gnrc_ipv6_nc_get_type(nc_entry) != GNRC_IPV6_NC_TYPE_GC)) {
- /* don't remove non-gc entrys on 6LRs:
- * https://tools.ietf.org/html/rfc6775#section-6 */
- gnrc_ndp_internal_set_state(nc_entry, GNRC_IPV6_NC_STATE_UNREACHABLE);
- return;
- }
- }
-#endif
+
+ /* For a 6LoWPAN router entries may be set to UNREACHABLE instead
+ * of removing them, since RFC6775, section 6
+ * (https://tools.ietf.org/html/rfc6775#section-6) says: "if NUD on
+ * the router determines that the host is UNREACHABLE (based on the
+ * logic in [RFC4861]), the NCE SHOULD NOT be deleted but rather
+ * retained until the Registration Lifetime expires." However, this
+ * "SHOULD NOT" is not implemented to circumvent NCEs going into
+ * UNREACHABLE forever and in order to save some memory in the
+ * neighbor cache. */
+
DEBUG("ndp: Remove nc entry %s for interface %" PRIkernel_pid "\n",
ipv6_addr_to_str(addr_str, &nc_entry->ipv6_addr, sizeof(addr_str)),
nc_entry->iface);
--
GitLab