blob: 394fa0732a33fabe9a882a43d1a6d8a13521ad78 [file] [log] [blame]
From a4a66c44eddb4cfbbf5341588646d90dee96dc84 Mon Sep 17 00:00:00 2001
From: Tim Stallard <>
Date: Fri, 3 Apr 2020 21:26:21 +0100
Subject: [PATCH] net: ipv6: do not consider routes via gateways for anycast
address check
commit 03e2a984b6165621f287fadf5f4b5cd8b58dcaba upstream.
The behaviour for what is considered an anycast address changed in
commit 45e4fd26683c ("ipv6: Only create RTF_CACHE routes after
encountering pmtu exception"). This now considers the first
address in a subnet where there is a route via a gateway
to be an anycast address.
This breaks path MTU discovery and traceroutes when a host in a
remote network uses the address at the start of a prefix
(eg 2600:: advertised as 2600::/48 in the DFZ) as ICMP errors
will not be sent to anycast addresses.
This patch excludes any routes with a gateway, or via point to
point links, like the behaviour previously from
rt6_is_gw_or_nonexthop in net/ipv6/route.c.
This can be tested with:
ip link add v1 type veth peer name v2
ip netns add test
ip netns exec test ip link set lo up
ip link set v2 netns test
ip link set v1 up
ip netns exec test ip link set v2 up
ip addr add 2001:db8::1/64 dev v1 nodad
ip addr add 2001:db8:100:: dev lo nodad
ip netns exec test ip addr add 2001:db8::2/64 dev v2 nodad
ip netns exec test ip route add unreachable 2001:db8:1::1
ip netns exec test ip route add 2001:db8:100::/64 via 2001:db8::1
ip netns exec test sysctl net.ipv6.conf.all.forwarding=1
ip route add 2001:db8:1::1 via 2001:db8::2
ping -I 2001:db8::1 2001:db8:1::1 -c1
ping -I 2001:db8:100:: 2001:db8:1::1 -c1
ip addr delete 2001:db8:100:: dev lo
ip netns delete test
Currently the first ping will get back a destination unreachable ICMP
error, but the second will never get a response, with "icmp6_send:
acast source" logged. After this patch, both get destination
unreachable ICMP replies.
Fixes: 45e4fd26683c ("ipv6: Only create RTF_CACHE routes after encountering pmtu exception")
Signed-off-by: Tim Stallard <>
Signed-off-by: David S. Miller <>
Signed-off-by: Paul Gortmaker <>
diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index ee7405e759ba..77c5a171703d 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -235,6 +235,7 @@ static inline bool ipv6_anycast_destination(const struct dst_entry *dst,
return rt->rt6i_flags & RTF_ANYCAST ||
(rt->rt6i_dst.plen < 127 &&
+ !(rt->rt6i_flags & (RTF_GATEWAY | RTF_NONEXTHOP)) &&
ipv6_addr_equal(&rt->rt6i_dst.addr, daddr));