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Re: [XFRM]: Always reroute in tunnel mode

To: "David S. Miller" <davem@xxxxxxxxxxxxx>
Subject: Re: [XFRM]: Always reroute in tunnel mode
From: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Date: Fri, 18 Feb 2005 20:53:44 +1100
Cc: Patrick McHardy <kaber@xxxxxxxxx>, netdev@xxxxxxxxxxx
In-reply-to: <20050217151122.098c6def.davem@xxxxxxxxxxxxx>
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On Thu, Feb 17, 2005 at 03:11:22PM -0800, David S. Miller wrote:
> I have to side with Patrick on this one.


> This is one of the fundamental tunnel behavior differences between
> Transport mode and Tunnel mode SAs.

I don't see it that way.  To me IPsec is about encapsulating a packet
so that it gets to the destination securely.  It shouldn't affect the
routing of the packet on the host itself.  Of course, once the packet
leaves the host the IPsec encapsulation will certainly affect its

In this respect, the difference between transport mode SAs and tunnel
mode SAs is simply that one adds an IP header while the other doesn't.

Ideally I should be able to only look at the routing table and determine
which interface/gateway a packet is going to be sent through.  As it is
I need to look at the routing table plus the IPsec database.

Put it another way, my solution to Patrick's inconsistency would be to
always inherit the routing decision from the top to the bottom of the
bundle.  For example, suppose you had

ip ro add \
        nexthop via dev eth0 \
        nexthop via dev eth0

Then the packets to should be sent via
regardless of what IPsec protections are applied to it.

This is something that can't be done in a clean way with the
current setup.  I'd like to see that available in Linux at some
point.  It'll have to be optional of course (selectable per-policy).

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