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Re: [22/*] [NETFILTER] Use correct IPsec MTU in TCPMSS

To: netdev@xxxxxxxxxxx
Subject: Re: [22/*] [NETFILTER] Use correct IPsec MTU in TCPMSS
From: Ludo Stellingwerff <ludo@xxxxxxxxxxxxx>
Date: Sun, 20 Mar 2005 17:32:13 +0100
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As an daily user of Patricks patches, I like to agree with Patricks
analysis about the loosing of flexibility with the choice not to use
virtual devices. In a real-life situation I had to revert to using
plain, unsave GRE-tunnels because of the complexity of using 2.6-ipsec
for the same purpose. I'm routing one of multiple defaultroutes over
this tunnel:) It felt like a relieve having a device to work with.

Just my 2 cents,

Patrick McHardy wrote:

| David S. Miller wrote:
|> On Fri, 18 Mar 2005 20:11:29 +1100 Herbert Xu
|> <herbert@xxxxxxxxxxxxxxxxxxx> wrote:
|>> BTW Patrick, how is the IPsec netfilter stuff going?
|> That boy is seriously backlogged, so I'm not sure how much time
|> he's gotten to work on that yet.
| Indeed, but in case of the netfilter patches that's not the
| problem. They are basically working fine, but I have doubts about
| submitting them. First, and most importantly, the input patch is
| incredible ugly. To recap, we want to pass the encapsulated packets
| to the netfilter hooks, then again the decapsulated packets after
| all decapsulation has been done. The current input patch makes
| packets that have been handled by IPsec skip the netfilter hooks
| until we know no further IPsec processing will be done (route is
| non-local or protocol handler is not marked as xfrm_prot). The
| packet is then marked as completely decapsulated and passed through
| the stack again and the plain packets go through netfilter again.
| There are a couple of problems with this approach:
| - decapsulated tunnel-mode packets go through the stack twice -
| netfilter only sees them once, everything else multiple times
| (statistics, packet sockets, ...) - racy, xfrm protocol could be
| registered after we determined decapsulation is done. - inefficient
| The second reason is that I'm not sure at all wether this is the
| way to go. With KLIPS-like IPsec-devices you can sniff the plain
| packets before they are handled by IPsec and you can perform
| traffic shaping on them. These two points are completely unhandled,
| and people seem to want them.
| So what's holding back these patches is getting some consensus on
| what exactly we want to do and finding a better method for
| determining when decapsulation is done. One possibility would be
| stealing packets in xfrm_policy_check(), but I haven't thought much
| about this yet.
| Regards Patrick

- --
Ludo Stellingwerff

V&S B.V. The Netherlands
ProTactive firewall solution.
Tel: +31 172 416116
Fax: +31 172 416124

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