From b208db0f27457cfded767368d6d3d13ca843920f Mon Sep 17 00:00:00 2001 From: Benjamin Valentin Date: Mon, 7 Jun 2021 16:53:34 +0200 Subject: [PATCH] gnrc_ipv6_auto_subnets: auto-configuration for nested subnets If we get a large (e.g. /62) prefix from e.g. DHCPv6, we can split it into subnets automatically to configure downstream interfaces. This allows for automatic configuration of daisy-chained nodes or nodes connected in a tree topology. To enable the feature, a new pseudo-module `gnrc_ipv6_auto_subnets` is provided. --- .../src/gnrc_ipv6_auto_subnets_simple.puml | 35 +++ .../src/gnrc_ipv6_auto_subnets_simple.svg | 1 + sys/net/gnrc/Makefile | 3 + sys/net/gnrc/Makefile.dep | 6 + .../gnrc/routing/ipv6_auto_subnets/Makefile | 3 + .../gnrc_ipv6_auto_subnets.c | 218 ++++++++++++++++++ 6 files changed, 266 insertions(+) create mode 100644 doc/doxygen/src/gnrc_ipv6_auto_subnets_simple.puml create mode 100644 doc/doxygen/src/gnrc_ipv6_auto_subnets_simple.svg create mode 100644 sys/net/gnrc/routing/ipv6_auto_subnets/Makefile create mode 100644 sys/net/gnrc/routing/ipv6_auto_subnets/gnrc_ipv6_auto_subnets.c diff --git a/doc/doxygen/src/gnrc_ipv6_auto_subnets_simple.puml b/doc/doxygen/src/gnrc_ipv6_auto_subnets_simple.puml new file mode 100644 index 000000000000..18c16e51d621 --- /dev/null +++ b/doc/doxygen/src/gnrc_ipv6_auto_subnets_simple.puml @@ -0,0 +1,35 @@ +' to generate SVG run plantuml -tsvg gnrc_ipv6_auto_subnets_simple.puml +@startuml +nwdiag { + + network level1 { + address = "2001:db8::/60"; + + router_a [address = "2001:db8::c8f4:13ff:fece:3f43", description = "1st level router"]; + leaf_a [address = "2001:db8::804b:fcff:feb6:43fb", description = "1st level leaf node"]; + } + + network level2 { + address = "2001:db8:0:8::/61"; + + router_a [address = "2001:db8:0:8:3c27:6dff:fe25:e95d"]; + router_b [address = "2001:db8:0:8:5075:35ff:fefa:30bc", description = "2nd level router"]; + } + + network level3 { + address = "2001:db8:0:c::/62"; + + router_b [address = "2001:db8:0:c:2ca3:9eff:fea9:68f7"]; + router_c [address = "2001:db8:0:c:fc33:13ff:fe93:5ae4", description = "3rd level router"]; + leaf_b1 [address = "2001:db8:0:c:209e:deff:fea9:fd1b", description = "3rd level leaf node"]; + leaf_b2 [address = "2001:db8:0:c:5491:a2ff:fe98:61a2", description = "3rd level leaf node"]; + } + + network level4 { + address = "2001:db8:0:e::/63"; + + router_c [address = "2001:db8:0:e:a8d9:e1ff:feab:d544"]; + leaf_c [address = "2001:db8:0:e:1cf5:33ff:fe7c:c70c", description = "4th level leaf node"]; + } +} +@enduml diff --git a/doc/doxygen/src/gnrc_ipv6_auto_subnets_simple.svg b/doc/doxygen/src/gnrc_ipv6_auto_subnets_simple.svg new file mode 100644 index 000000000000..1ec775bdd134 --- /dev/null +++ b/doc/doxygen/src/gnrc_ipv6_auto_subnets_simple.svg @@ -0,0 +1 @@ +level12001:db8::/60level22001:db8:0:8::/61level32001:db8:0:c::/62level42001:db8:0:e::/632001:db8::c8f4:13ff:fece:3f432001:db8:0:8:3c27:6dff:fe25:e95d2001:db8::804b:fcff:feb6:43fb2001:db8:0:8:5075:35ff:fefa:30bc2001:db8:0:c:2ca3:9eff:fea9:68f72001:db8:0:c:fc33:13ff:fe93:5ae42001:db8:0:e:a8d9:e1ff:feab:d5442001:db8:0:c:209e:deff:fea9:fd1b2001:db8:0:c:5491:a2ff:fe98:61a22001:db8:0:e:1cf5:33ff:fe7c:c70c1st level router1st level leaf node2nd level router3rd level router3rd level leaf node3rd level leaf node4th level leaf node diff --git a/sys/net/gnrc/Makefile b/sys/net/gnrc/Makefile index e079b12dc650..8c4242a83ea9 100644 --- a/sys/net/gnrc/Makefile +++ b/sys/net/gnrc/Makefile @@ -88,6 +88,9 @@ endif ifneq (,$(filter gnrc_rpl_p2p,$(USEMODULE))) DIRS += routing/rpl/p2p endif +ifneq (,$(filter gnrc_ipv6_auto_subnets,$(USEMODULE))) + DIRS += routing/ipv6_auto_subnets +endif ifneq (,$(filter gnrc_sixlowpan,$(USEMODULE))) DIRS += network_layer/sixlowpan endif diff --git a/sys/net/gnrc/Makefile.dep b/sys/net/gnrc/Makefile.dep index c9e7f352adde..05c501eabd36 100644 --- a/sys/net/gnrc/Makefile.dep +++ b/sys/net/gnrc/Makefile.dep @@ -113,6 +113,12 @@ ifneq (,$(filter gnrc_rpl,$(USEMODULE))) USEMODULE += evtimer endif +ifneq (,$(filter gnrc_ipv6_auto_subnets,$(USEMODULE))) + USEMODULE += gnrc_ipv6_nib_rtr_adv_pio_cb + CFLAGS += -DCONFIG_GNRC_IPV6_NIB_ADV_ROUTER=0 + CFLAGS += -DCONFIG_GNRC_IPV6_NIB_ADD_RIO_IN_LAST_RA=1 +endif + ifneq (,$(filter gnrc_netif,$(USEMODULE))) USEMODULE += netif USEMODULE += l2util diff --git a/sys/net/gnrc/routing/ipv6_auto_subnets/Makefile b/sys/net/gnrc/routing/ipv6_auto_subnets/Makefile new file mode 100644 index 000000000000..fe99c627cbc8 --- /dev/null +++ b/sys/net/gnrc/routing/ipv6_auto_subnets/Makefile @@ -0,0 +1,3 @@ +MODULE = gnrc_ipv6_auto_subnets + +include $(RIOTBASE)/Makefile.base diff --git a/sys/net/gnrc/routing/ipv6_auto_subnets/gnrc_ipv6_auto_subnets.c b/sys/net/gnrc/routing/ipv6_auto_subnets/gnrc_ipv6_auto_subnets.c new file mode 100644 index 000000000000..635892f78c15 --- /dev/null +++ b/sys/net/gnrc/routing/ipv6_auto_subnets/gnrc_ipv6_auto_subnets.c @@ -0,0 +1,218 @@ +/* + * Copyright (C) 2021 ML!PA Consulting GmbH + * + * This file is subject to the terms and conditions of the GNU Lesser + * General Public License v2.1. See the file LICENSE in the top level + * directory for more details. + */ + +/** + * @defgroup net_gnrc_ipv6_auto_subnets Simple-Subnet auto-configuration + * @ingroup net_gnrc + * @brief Automatic configuration for cascading subnets + * + * About + * ===== + * + * This module provides an automatic configuration for networks with a simple + * tree topology. + * + * If a sufficiently large IPv6 prefix (> /64) is provided via Router Advertisements, + * a routing node with this module will automatically configure subnets from it + * by dividing it into sub-prefixes for each downstream interface. + * + * There can only be a single routing node on each level of the network but an + * arbitrary number of leaf nodes. + * + * ![Example Topology](gnrc_ipv6_auto_subnets_simple.svg) + * + * The downstream network(s) receive the sub-prefix via Router Advertisements + * and the process repeats until the bits of the prefix are exhausted. + * The smallest subnet must still have a /64 prefix. + * + * The new subnet must no longer be considered on-link by the hosts in the + * parent network. + * Therefore the downstream router will send a router advertisement with only + * a Route Information Option included to the upstream network. + * The Route Information Option contains the prefix of the downstream network + * so that upstream routers will no longer consider hosts in this subnet on-link + * but instead will use the downstream router to route to the new subnet. + * + * Usage + * ===== + * + * Simply add the `gnrc_ipv6_auto_subnets` module to the code of the nodes that + * should act as routers in the cascading network. + * The upstream network will be automatically chosen as the one that first + * receives a router advertisement. + * + * @{ + * + * @file + * @author Benjamin Valentin + */ + +#include "net/gnrc/ipv6/nib.h" +#include "net/gnrc/ndp.h" + +#define ENABLE_DEBUG 0 +#include "debug.h" + +static char addr_str[IPV6_ADDR_MAX_STR_LEN]; + +static void _init_sub_prefix(ipv6_addr_t *out, + const ipv6_addr_t *prefix, uint8_t bits, + uint8_t idx, uint8_t idx_bits) +{ + uint8_t bytes = bits / 8; + uint8_t rem = bits % 8; + int8_t shift = 8 - rem - idx_bits; + + /* first copy old prefix */ + memset(out, 0, sizeof(*out)); + ipv6_addr_init_prefix(out, prefix, bits); + + /* if new bits are between bytes, first copy over the most significant bits */ + if (shift < 0) { + out->u8[bytes] |= idx >> -shift; + out->u8[++bytes] = 0; + shift += 8; + } + + /* shift remaining bits at the end of the prefix */ + out->u8[bytes] |= idx << shift; +} + +static bool _remove_old_prefix(gnrc_netif_t *netif, + const ipv6_addr_t *pfx, uint8_t pfx_len, + gnrc_pktsnip_t **ext_opts) +{ + gnrc_ipv6_nib_pl_t entry; + gnrc_pktsnip_t *tmp; + void *state = NULL; + ipv6_addr_t old_pfx; + uint8_t old_pfx_len = 0; + + /* iterate prefix list to see if the prefix already exists */ + while (gnrc_ipv6_nib_pl_iter(netif->pid, &state, &entry)) { + uint8_t match_len = ipv6_addr_match_prefix(&entry.pfx, pfx); + + /* The prefix did not change - nothing to do here */ + if (match_len >= pfx_len && pfx_len == entry.pfx_len) { + return true; + } + + /* find prefix that is closest to the new prefix */ + if (match_len > old_pfx_len) { + old_pfx_len = entry.pfx_len; + old_pfx = entry.pfx; + } + } + + /* no prefix found */ + if (old_pfx_len == 0) { + return false; + } + + DEBUG("auto_subnets: remove old prefix %s/%u\n", + ipv6_addr_to_str(addr_str, &old_pfx, sizeof(addr_str)), old_pfx_len); + + /* invalidate old prefix in RIO */ + tmp = gnrc_ndp_opt_ri_build(&old_pfx, old_pfx_len, 0, + NDP_OPT_RI_FLAGS_PRF_NONE, *ext_opts); + if (tmp) { + *ext_opts = tmp; + } + + /* remove the prefix */ + gnrc_ipv6_nib_pl_del(netif->pid, &old_pfx, old_pfx_len); + + return false; +} + +static void _configure_subnets(uint8_t subnets, gnrc_netif_t *upstream, + const ndp_opt_pi_t *pio) +{ + gnrc_netif_t *downstream = NULL; + gnrc_pktsnip_t *ext_opts = NULL; + const ipv6_addr_t *prefix = &pio->prefix; + uint32_t valid_ltime = byteorder_ntohl(pio->valid_ltime); + uint32_t pref_ltime = byteorder_ntohl(pio->pref_ltime); + const uint8_t prefix_len = pio->prefix_len; + uint8_t new_prefix_len, subnet_len; + + DEBUG("auto_subnets: create %u subnets\n", subnets); + + /* Calculate remaining prefix length. + * For n subnets we consume floor(log_2 n) + 1 bits. + * To calculate floor(log_2 n) quickly, find the position of the + * most significant set bit by counting leading zeros. + */ + subnet_len = 32 - __builtin_clz(subnets); + new_prefix_len = prefix_len + subnet_len; + + if (new_prefix_len > 64) { + DEBUG("auto_subnets: can't split /%u into %u subnets\n", prefix_len, subnets); + return; + } + + while ((downstream = gnrc_netif_iter(downstream))) { + gnrc_pktsnip_t *tmp; + ipv6_addr_t new_prefix; + + if (downstream == upstream) { + continue; + } + + /* create subnet from upstream prefix */ + _init_sub_prefix(&new_prefix, prefix, prefix_len, subnets--, subnet_len); + + DEBUG("auto_subnets: configure prefix %s/%u on %u\n", + ipv6_addr_to_str(addr_str, &new_prefix, sizeof(addr_str)), + new_prefix_len, downstream->pid); + + /* first remove old prefix if the prefix changed */ + _remove_old_prefix(downstream, &new_prefix, new_prefix_len, &ext_opts); + + /* configure subnet on downstream interface */ + gnrc_netif_ipv6_add_prefix(downstream, &new_prefix, new_prefix_len, + valid_ltime, pref_ltime); + + /* start advertising subnet */ + gnrc_ipv6_nib_change_rtr_adv_iface(downstream, true); + + /* add route information option with new subnet */ + tmp = gnrc_ndp_opt_ri_build(&new_prefix, new_prefix_len, valid_ltime, + NDP_OPT_RI_FLAGS_PRF_NONE, ext_opts); + if (tmp == NULL) { + DEBUG("auto_subnets: No space left in packet buffer. Not adding RIO\n"); + } else { + ext_opts = tmp; + } + } + + /* immediately send an RA with RIO */ + if (ext_opts) { + gnrc_ndp_rtr_adv_send(upstream, NULL, + &ipv6_addr_all_nodes_link_local, true, ext_opts); + } else { + DEBUG("auto_subnets: Options empty, not sending RA\n"); + } +} + +void gnrc_ipv6_nib_rtr_adv_pio_cb(gnrc_netif_t *upstream, const ndp_opt_pi_t *pio) +{ + /* create a subnet for each downstream interface */ + unsigned subnets = gnrc_netif_numof() - 1; + + if (subnets == 0) { + return; + } + + if (pio->valid_ltime.u32 == 0) { + return; + } + + _configure_subnets(subnets, upstream, pio); +} +/** @} */