[Openswan dev] ipsec0 dropped packets as a result of icmp unreachable misfires

[Paul Wouters]

On Tue, 3 Jan 2006, Marco Berizzi wrote:

> I have enabled klipsdebug=all, and I have found why I see dropped TX packets
> on ipsec0 interface.
> This is my network diagram:
>
> ---priv1_net---|swan1 box|---eth0_pub_ip-*internet*-pub_ip_eth0---|swan2
> box|---priv2_net
>
> I'm pinging a non-existent system on the priv1_net from a priv2_net host and
> the swan1
> box is generating an icmp host unreachable packet with source IP=eth0_pub_ip
> and
> destination IP=priv2_net host. This packet is then routed through ipsec0 and
> it is
> dropped by KLIPS. I don't understand why the linux box is generating the icmp
> packet
> with source ip=eth0_pub and not with the priv1_net ip assigned to itself (on
> eth1). Is this
> the correct behaviour? What should I do to have the icmp unreach response back
> to the
> original client on the priv2_net (if possible)?

that's odd, it shouldnt be accepted by klips as there is no policy for it.

A workaround I can think of is to use leftsourceip=priv1_netip on swan1 box, which
might trigger the icmp message source address to be the private instead of public
address.

Alternatively, you can create eth0_pub_ip-priv2subnet tunnels (eg create not only
subnet-subnet, but host-subnet, subnet-host and host-host tunnels) to cover the
current icmp packet with an ipsec policy.

I am not sure if this should be considered a bug in openswan or in the linux kernel.

Anyone on the dev list have the answer to this one?

Paul