multi-home difficulty

d tbsky tbskyd at
Thu Nov 23 18:06:59 CET 2017

2017-11-23 7:35 GMT+08:00 Jason A. Donenfeld <Jason at>:
> On Tue, Nov 21, 2017 at 3:35 PM, d tbsky <tbskyd at> wrote:
>> thanks for the quick reply. my wireguard configuration is in the
>> previous mail, so I think the linux firewall part is what you want.
> Right. So if you can give me minimal instructions on how to set up a
> box that exhibits the buggy behavior you're seeing, I can try to fix
> it.
> Jason

sorry for the delay.  I try to make a minimal config to reproduce the
problem in our firewall, but it's not easy. the communication
sometimes works, sometimes failed. suddenly I remember many years ago
I got similar problems with openvpn. according the manual pages of

              Configure a multi-homed UDP server.  This option needs
to be used when a server has more  than  one  IP
              address  (e.g. multiple interfaces, or secondary IP
addresses), and is not using --local to force bind‐
              ing to one specific address only.  This option will add
some extra lookups to the packet path to ensure
              that  the UDP reply packets are always sent from the
address that the client is talking to. This is not
              supported on all platforms, and it adds more processing,
so it's not enabled by default.

              Note: this option is only relevant for UDP servers.

              Note 2: if you do an IPv6+IPv4 dual-stack bind on a
Linux machine with multiple IPv4  address,  connec‐
              tions  to  IPv4 addresses will not work right on kernels
before 3.15, due to missing kernel support for
              the IPv4-mapped case (some distributions have ported
this to earlier kernel versions, though).

  I forgot these. many strange things happen if you didn't bind
specific ip, even with "--multihome"

  finally I made a environment for you to test. my OS is rehl 7.4,
kernel version 3.10.0-693.5.2

  1. build a virtual rhel 7.4 box, bind 2 virtio nic to it. (single
nic won't show the problem, I don't now why).
  2. stop NetworkManager
  3. setup network environment like below(skip eth0, setup eth1 with
two ip addresses):

ip addr flush dev eth1
ip addr add dev eth1
ip addr add dev eth1
ip link set eth1 up
ip route add default via

ip link add wg0 type wireguard
ip addr add peer dev wg0
wg setconf wg0 /root/server.conf
ip link set wg0 up

/root/server.conf like below:
PrivateKey = ****
ListenPort = 51820
PublicKey = ****
AllowedIPs =

    4. setup wireguard at client site. client.conf like below:

PrivateKey = ****
ListenPort = 51820
PublicKey = ****
Endpoint =
AllowedIPs =

    5. at client site, "ping".

    6. at server site, "modprobe nf_conntrack_ipv4;cat
/proc/net/nf_conntrack | grep 51820":

ipv4     2 udp      17 29 src= dst= sport=51820
dport=51820 [UNREPLIED] src= dst= sport=51820
dport=51820 mark=0 zone=0 use=2
ipv4     2 udp      17 29 src= dst= sport=51820
dport=51820 [UNREPLIED] src= dst= sport=51820
dport=51820 mark=0 zone=0 use=2

   I don't know if you can reproduce in your environment.
   hope  wireguard can bind to specific ip in the future..


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