Antony Antony via Devel <devel@linux-ipsec.org> wrote:
    > When enabling support for xfrm lookup using reverse ICMP payload,
    > We have identified an issue where the source address of the IPv4 e.g
    > "Destination Host Unreachable" message is incorrect. The IPv6 appear
    > to do the right thing.

One thing that operators of routers with a multitude of interfaces want to do
is send all ICMP messages from a specific IP address.  Often the public
address, that has the sane reverse DNS name.
AFAIK, this is not an option on Linux, but Cisco/Juniper/etc. devices usually
can do this.  I can't recall how today. (I was actually looking that up this week)

This can conflict however, with the need to get the result back into the
tunnel.  I don't have a good answer, except that we probably need a fair bit
of flexibility, with some good automatically discovered defaults.