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nd6: improve router selection

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Previously, IPv6 routing could select a next-hop router on a netif
that was down or disconnected, potentially resulting in packets being
dropped unnecessarily. This patch changes router selection to take
into account the state of the router's associated netif, eliminating
such unnecessary packet loss.

Also, this patch fixes the test for router validity, which was
erroneously based on the router's invalidation timer rather than its
neighbor cache entry state. Given that an expired router has no
associated neighbor cache entry, no invalid routers would previously
ever be returned.

Finally, this patch also adds round-robin selection of routers that
are not known to be reachable or probably reachable, as per RFC 4861
Sec. 6.3.6 point (2). Support for this feature was partially present
but not actually functional.
This commit is contained in:
David van Moolenbroek 2016-12-30 14:01:34 +00:00 committed by Dirk Ziegelmeier
parent 901664eca1
commit 22c2fd1b58
2 changed files with 52 additions and 37 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
src/core/ipv6/ip6.c
View File

@ -145,7 +145,7 @@ ip6_route(const ip6_addr_t *src, const ip6_addr_t *dest)
/* Get the netif for a suitable router. */
netif = nd6_find_route(dest);
if ((netif != NULL) && netif_is_up(netif) && netif_is_link_up(netif)) {
if (netif != NULL) {
return netif;
}

87
src/core/ipv6/nd6.c
View File

@ -1513,6 +1513,11 @@ nd6_is_prefix_in_netif(const ip6_addr_t *ip6addr, struct netif *netif)
/**
* Select a default router for a destination.
*
* This function is used both for routing and for finding a next-hop target for
* a packet. In the former case, the given netif is NULL, and the returned
* router entry must be for a netif suitable for sending packets (up, link up).
* In the latter case, the given netif is not NULL and restricts router choice.
*
* @param ip6addr the destination address
* @param netif the netif for the outgoing packet, if known
* @return the default router entry index, or -1 if no suitable
@ -1521,48 +1526,58 @@ nd6_is_prefix_in_netif(const ip6_addr_t *ip6addr, struct netif *netif)
static s8_t
nd6_select_router(const ip6_addr_t *ip6addr, struct netif *netif)
{
s8_t i;
/* last_router is used for round-robin router selection (as recommended
* in RFC). This is more robust in case one router is not reachable,
* we are not stuck trying to resolve it. */
struct netif *router_netif;
s8_t i, j, valid_router;
static s8_t last_router;
(void)ip6addr; /* @todo match preferred routes!! (must implement ND6_OPTION_TYPE_ROUTE_INFO) */
LWIP_UNUSED_ARG(ip6addr); /* @todo match preferred routes!! (must implement ND6_OPTION_TYPE_ROUTE_INFO) */
/* @todo: implement default router preference */
/* Look for reachable routers. */
/* Look for valid routers. A reachable router is preferred. */
valid_router = -1;
for (i = 0; i < LWIP_ND6_NUM_ROUTERS; i++) {
if (++last_router >= LWIP_ND6_NUM_ROUTERS) {
last_router = 0;
}
if ((default_router_list[i].neighbor_entry != NULL) &&
(netif != NULL ? netif == default_router_list[i].neighbor_entry->netif : 1) &&
(default_router_list[i].invalidation_timer > 0) &&
(default_router_list[i].neighbor_entry->state == ND6_REACHABLE)) {
return i;
/* Is the router netif both set and apppropriate? */
if (default_router_list[i].neighbor_entry != NULL) {
router_netif = default_router_list[i].neighbor_entry->netif;
if ((router_netif != NULL) && (netif != NULL ? netif == router_netif :
(netif_is_up(router_netif) && netif_is_link_up(router_netif)))) {
/* Is the router valid, i.e., reachable or probably reachable as per
* RFC 4861 Sec. 6.3.6? Note that we will never return a router that
* has no neighbor cache entry, due to the netif association tests. */
if (default_router_list[i].neighbor_entry->state != ND6_INCOMPLETE) {
/* Is the router known to be reachable? */
if (default_router_list[i].neighbor_entry->state == ND6_REACHABLE) {
return i; /* valid and reachable - done! */
} else if (valid_router < 0) {
valid_router = i; /* valid but not known to be reachable */
}
}
}
}
}
/* Look for router in other reachability states, but still valid according to timer. */
for (i = 0; i < LWIP_ND6_NUM_ROUTERS; i++) {
if (++last_router >= LWIP_ND6_NUM_ROUTERS) {
last_router = 0;
}
if ((default_router_list[i].neighbor_entry != NULL) &&
(netif != NULL ? netif == default_router_list[i].neighbor_entry->netif : 1) &&
(default_router_list[i].invalidation_timer > 0)) {
return i;
}
if (valid_router >= 0) {
return valid_router;
}
/* Look for any router for which we have any information at all. */
for (i = 0; i < LWIP_ND6_NUM_ROUTERS; i++) {
if (++last_router >= LWIP_ND6_NUM_ROUTERS) {
last_router = 0;
/* last_router is used for round-robin selection of incomplete routers, as
* recommended in RFC 4861 Sec. 6.3.6 point (2). Advance only when picking a
* route, to select the same router as next-hop target in the common case. */
if ((netif == NULL) && (++last_router >= LWIP_ND6_NUM_ROUTERS)) {
last_router = 0;
}
i = last_router;
for (j = 0; j < LWIP_ND6_NUM_ROUTERS; j++) {
if (default_router_list[i].neighbor_entry != NULL) {
router_netif = default_router_list[i].neighbor_entry->netif;
if ((router_netif != NULL) && (netif != NULL ? netif == router_netif :
(netif_is_up(router_netif) && netif_is_link_up(router_netif)))) {
return i;
}
}
if (default_router_list[i].neighbor_entry != NULL &&
(netif != NULL ? netif == default_router_list[i].neighbor_entry->netif : 1)) {
return i;
if (++i >= LWIP_ND6_NUM_ROUTERS) {
i = 0;
}
}
@ -1573,8 +1588,8 @@ nd6_select_router(const ip6_addr_t *ip6addr, struct netif *netif)
/**
* Find a router-announced route to the given destination.
*
* The caller is responsible for checking whether the returned netif, if any,
* is in a suitable state (up, link up) to be used for packet transmission.
* If a suitable route is found, the returned netif is guaranteed to be in a
* suitable state (up, link up) to be used for packet transmission.
*
* @param ip6addr the destination IPv6 address
* @return the netif to use for the destination, or NULL if none found
@ -1586,9 +1601,9 @@ nd6_find_route(const ip6_addr_t *ip6addr)
i = nd6_select_router(ip6addr, NULL);
if (i >= 0) {
if (default_router_list[i].neighbor_entry != NULL) {
return default_router_list[i].neighbor_entry->netif; /* may be NULL */
}
LWIP_ASSERT("selected router must have a neighbor entry",
default_router_list[i].neighbor_entry != NULL);
return default_router_list[i].neighbor_entry->netif;
}
return NULL;