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Commit a5a81f0b authored by Paul Marks's avatar Paul Marks Committed by David S. Miller

ipv6: Fix default route failover when CONFIG_IPV6_ROUTER_PREF=n

I believe this commit from 2008 was incorrect:;a=commitdiff;h=398bcbebb6f721ac308df1e3d658c0029bb74503

When CONFIG_IPV6_ROUTER_PREF is disabled, the kernel should follow
RFC4861 section 6.3.6: if no route is NUD_VALID, then traffic should be
sprayed across all routers (indirectly triggering NUD) until one of them
becomes NUD_VALID.

However, the following experiment demonstrates that this does not work:

1) Connect to an IPv6 network.
2) Change the router's MAC (and link-local) address.

The kernel will lock onto the first router and never try the new one, even
if the first becomes unreachable.  This patch fixes the problem by
allowing rt6_check_neigh() to return 0; if all routers return 0, then
rt6_select() will fall back to round-robin behavior.

This patch should have no effect when CONFIG_IPV6_ROUTER_PREF=y.

Note that rt6_check_neigh() is only used in a boolean context, so I've
changed its return type accordingly.
Signed-off-by: default avatarPaul Marks <>
Signed-off-by: default avatarDavid S. Miller <>
parent 5d097109
......@@ -544,35 +544,32 @@ static inline int rt6_check_dev(struct rt6_info *rt, int oif)
return 0;
static inline int rt6_check_neigh(struct rt6_info *rt)
static inline bool rt6_check_neigh(struct rt6_info *rt)
struct neighbour *neigh;
int m;
bool ret = false;
neigh = rt->n;
if (rt->rt6i_flags & RTF_NONEXTHOP ||
!(rt->rt6i_flags & RTF_GATEWAY))
m = 1;
ret = true;
else if (neigh) {
if (neigh->nud_state & NUD_VALID)
m = 2;
ret = true;
else if (neigh->nud_state & NUD_FAILED)
m = 0;
else if (!(neigh->nud_state & NUD_FAILED))
ret = true;
m = 1;
} else
m = 0;
return m;
return ret;
static int rt6_score_route(struct rt6_info *rt, int oif,
int strict)
int m, n;
int m;
m = rt6_check_dev(rt, oif);
if (!m && (strict & RT6_LOOKUP_F_IFACE))
......@@ -580,8 +577,7 @@ static int rt6_score_route(struct rt6_info *rt, int oif,
m |= IPV6_DECODE_PREF(IPV6_EXTRACT_PREF(rt->rt6i_flags)) << 2;
n = rt6_check_neigh(rt);
if (!n && (strict & RT6_LOOKUP_F_REACHABLE))
if (!rt6_check_neigh(rt) && (strict & RT6_LOOKUP_F_REACHABLE))
return -1;
return m;
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