Overlapping AllowedIPs Configuration

[Henning Reich]

No, I think its correct behaviour.
If you have overlapping networks  the more specific route is preferred.
10.10.10.0/24 overrule 10.10.0.0/16.
If the subnets are the same, the last one is the more specific (because
most recent one) and should be used.

And in germany, we say (literal translation): You're allowed to shoot
yourself in the knee.
(to be self-defeating) :-)



Aleksa Sarai <cyphar at cyphar.com> schrieb am Sa., 11. Mai 2019, 15:09:

> Hi all,
>
> I just found out that WireGuard apparently allows you to configure an
> interface that has peers with overlapping AllowedIPs ranges -- which
> obviously won't work with cryptokey routing -- but additionally is
> strange since I feel this should cause an error when configuring the
> interface.
>
> In my case, I accidentally used /32 when generating the IPv6 addresses
> of my clients and ended up with a config like:
>
>   [Interface]
>   Address = 10.13.37.1/32,fd00:dead:beef:cafe::1/64
>   ListenPort = 51820
>   PrivateKey = [key]
>
>   # Peer A.
>   [Peer]
>   PublicKey = [pub]
>   PreSharedKey = [psk]
>   AllowedIPs = 10.13.40.1/32,fd00:dead:beef:1000::/32
>
>   # Peer B.
>   [Peer]
>   PublicKey = [pub]
>   PreSharedKey = [psk]
>   AllowedIPs = 10.13.41.1/32,fd00:dead:beef:1001::/32
>
> This config is wrong (because both peers have overlapping addresses
> specified for AllowedIPs), but wireguard will happily accept it:
>
>   % wg-quick up wg-foo
>   [#] ip link add wg-yavin type wireguard
>   [#] wg setconf wg-yavin /dev/fd/63
>   [#] ip address add 10.13.37.1/32 dev wg-yavin
>   [#] ip address add fd00:dead:beef:cafe::1/64 dev wg-yavin
>   [#] ip link set mtu 1420 up dev wg-yavin
>   [#] ip route add fd42:dead::/32 dev wg-yavin
>   [#] ip route add 10.13.41.1/32 dev wg-yavin
>   [#] ip route add 10.13.40.1/32 dev wg-yavin
>
> This configuration results in only one of the peers actually being given
> the IPv6 range, but I feel like "wg setconf" should've rejected this
> configuration.
>
>   % wg
>   interface: wg-foo
>     public key: [pub]
>     private key: (hidden)
>     listening port: 51820
>
>   peer: [peer A]
>     preshared key: (hidden)
>     allowed ips: 10.13.40.1/32
>
>   peer: [peer B]
>     preshared key: (hidden)
>     allowed ips: 10.13.41.1/32, fd42:dead::/32
>
> --
> Aleksa Sarai
> Senior Software Engineer (Containers)
> SUSE Linux GmbH
> <https://www.cyphar.com/>
> _______________________________________________
> WireGuard mailing list
> WireGuard at lists.zx2c4.com
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>
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