ip6: fix PMTU discovery when using /127 subnets
The definition of an "anycast destination address" has been tweaked as a
side-effect of commit 2647a9b07032 ("ipv6: Remove external dependency on
rt6i_gateway and RTF_ANYCAST"). The first address of a point-to-point
/127 subnet is now considered as an anycast address. This prevents
ICMPv6 errors to be returned to a sender of such a subnet and breaks
PMTU discovery.
This can be reproduced with:
ip link add name out6 type veth peer name in6
ip link add name out7 type veth peer name in7
ip link set mtu 1400 dev out7
ip link set mtu 1400 dev in7
ip netns add next-hop
ip netns add next-next-hop
ip link set netns next-hop dev in6
ip link set netns next-hop dev out7
ip link set netns next-next-hop dev in7
ip link set up dev out6
ip addr add 2001:db8:1::12/127 dev out6
ip netns exec next-hop ip link set up dev in6
ip netns exec next-hop ip link set up dev out7
ip netns exec next-hop ip addr add 2001:db8:1::13/127 dev in6
ip netns exec next-hop ip addr add 2001:db8:1::14/127 dev out7
ip netns exec next-hop ip route add default via 2001:db8:1::15
ip netns exec next-hop sysctl -qw net.ipv6.conf.all.forwarding=1
ip netns exec next-next-hop ip link set up dev in7
ip netns exec next-next-hop ip addr add 2001:db8:1::15/127 dev in7
ip netns exec next-next-hop ip addr add 2001:db8:1::50/128 dev in7
ip netns exec next-next-hop ip route add default via 2001:db8:1::14
ip netns exec next-next-hop sysctl -qw net.ipv6.conf.all.forwarding=1
ip route add 2001:db8:1::48/123 via 2001:db8:1::13
sleep 4
ping -M do -s 1452 -c 3 2001:db8:1::50 || true
ip route get 2001:db8:1::50
Before the patch, we get:
2001:db8:1::50 from :: via 2001:db8:1::13 dev out6 src 2001:db8:1::12 metric 1024 pref medium
After the patch, we get:
2001:db8:1::50 via 2001:db8:1::13 dev out6 src 2001:db8:1::12 metric 0
cache expires 578sec mtu 1400 pref medium
Fixes: 2647a9b07032 ("ipv6: Remove external dependency on rt6i_gateway and RTF_ANYCAST")
Signed-off-by: Vincent Bernat <vincent@bernat.im>
Signed-off-by: David S. Miller <davem@davemloft.net>
1 file changed
