From: "David S. Miller" <davem@redhat.com>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: kuznet@ms2.inr.ac.ru, herbert@gondor.apana.org.au,
jmorris@redhat.com, netdev@oss.sgi.com
Subject: Re: IPsec and Path MTU
Date: Thu, 17 Jun 2004 10:58:43 -0700 [thread overview]
Message-ID: <20040617105843.314dfe30.davem@redhat.com> (raw)
In-Reply-To: <E1BajZO-0001UK-00@gondolin.me.apana.org.au>
On Thu, 17 Jun 2004 09:11:50 +1000
Herbert Xu <herbert@gondor.apana.org.au> wrote:
> This is what prompted me to look at this two months ago. The stack
> assumes that the MTU for an xfrm dst is equal to
>
> dst_pmtu(dst) - dst->header_len - dst->trailer_len
>
> But this is not true for ESP due to block padding. The trailer_len
> is variable and the one we store in trailer_len is not the maximum.
>
> There are two approaches to this problem. We can either store the
> maximum trailer_len, or make dst_pmtu(dst) return the correct MTU
> directly.
>
> The former is simple to do, but has the disadvantage of wasting
> bandwidth up to a block. The latter looks non-trivial, but is
> pretty simple once we solve the following problems.
Do you see what xfrm_get_mss() does? It calls into x->type->get_max_size()
and this is where ESP reports this kind of thing (re: block padding).
next prev parent reply other threads:[~2004-06-17 17:58 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-06-15 12:43 IPsec and Path MTU Herbert Xu
2004-06-15 14:50 ` Michael Richardson
2004-06-16 11:43 ` Herbert Xu
2004-06-16 14:43 ` Michael Richardson
2004-06-18 7:35 ` Glen Turner
2004-06-16 12:10 ` Herbert Xu
2004-06-16 14:12 ` James Morris
2004-06-16 20:23 ` Alexey Kuznetsov
2004-06-16 20:49 ` David S. Miller
2004-06-16 23:11 ` Herbert Xu
2004-06-17 17:58 ` David S. Miller [this message]
2004-06-17 21:31 ` Herbert Xu
2004-06-17 22:22 ` David S. Miller
2004-06-17 23:09 ` Herbert Xu
2004-06-16 19:56 ` Alexey Kuznetsov
2004-06-16 23:13 ` Herbert Xu
2004-06-17 19:01 ` Alexey Kuznetsov
2004-06-17 21:38 ` Herbert Xu
2004-06-17 22:29 ` David S. Miller
2004-06-17 23:12 ` Herbert Xu
2004-06-17 23:14 ` David S. Miller
2004-06-17 23:18 ` Herbert Xu
[not found] ` <20040618202551.GA2733@ms2.inr.ac.ru>
2004-06-18 22:21 ` Herbert Xu
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