net: Evict neighbor entries on carrier down

When a link's carrier goes down it could be a sign of the port changing
networks. If the new network has overlapping addresses with the old one,
then the kernel will continue trying to use neighbor entries established
based on the old network until the entries finally age out - meaning a
potentially long delay with communications not working.

This patch evicts neighbor entries on carrier down with the exception of
those marked permanent. Permanent entries are managed by userspace (either
an admin or a routing daemon such as FRR).

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 51863ada15a4..a25cfdd47c89 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -1784,6 +1784,8 @@ static int ndisc_netdev_event(struct notifier_block *this, unsigned long event,
                 change_info = ptr;
                 if (change_info->flags_changed & IFF_NOARP)
                         neigh_changeaddr(&nd_tbl, dev);
+                if (!netif_carrier_ok(dev))
+                        neigh_carrier_down(&nd_tbl, dev);
                 break;
         case NETDEV_DOWN:
                 neigh_ifdown(&nd_tbl, dev);