[strongSwan] No packets transmitted for a while over IPv6 after connection establishment

[Jason White]

Adding extra information to my problem report below:
Jason White  <jason at jasonjgw.net> wrote:
>
>1. The connection is established in tunnel mode between my machine and a
>remote host, with StrongSwan 5.0.4 on both sides (debian kernel 3.8.13 on my
>side). Usually, the connection is established properly but sometimes there are
>retransmissions and timeouts when it reaches the child SA stage.
>
>2. After the connection is established, my machine can receive packets over
>the tunnel successfully from the remote host, but it doesn't send out any
>packets at all. Tshark shows no attempt to send out echo requests when I ping
>the remote host, for example. Ip xfrm commands show that everything is
>set up as it should be.
>

To clarify, if I ping the remote host, no packets appear on the ppp0 interface
(which is the ADSL connection). However, on the loopback (lo) interface, I see
a packet corresponding to each attempt to send out an echo request: ICMPv6 274 Destination Unreachable (Address unreachable)
>3. After about 10-15 minutes, suddenly my host is able to send packets over
>the tunnel and everything works. So there's a timeout somewhere or perhaps
>something gets renegotiated.
>
>4. If I copy the configuration and change all of the addresses to the
>respective host IPv4 addresses, the connection is established straight away
>and works fine.

I've also tried setting the MTU to 1500 but with no effect on the IPv6 issue.

Any suggestions? I can provide further configuration information if desired.