From: David Ahern <dsa@cumulusnetworks•com>
To: Tom Herbert <tom@herbertland•com>
Cc: Linux Kernel Network Developers <netdev@vger•kernel.org>
Subject: Re: [PATCH 2/2 v2] net: Remove VRF change to udp_sendmsg
Date: Wed, 9 Sep 2015 19:10:04 -0600 [thread overview]
Message-ID: <55F0D86C.90903@cumulusnetworks.com> (raw)
In-Reply-To: <CALx6S35Fwu5QsR-W=0LVzvZv_PGqbV3TGR9T5YRU65QCY0OgzQ@mail.gmail.com>
On 9/9/15 6:51 PM, Tom Herbert wrote:
> It is NAT since you are changing the source address and modifying the
> transport protocol checksum below IP and transport layer. There are a
> bunch of side effects that you would need to consider. This is
> creating custom APIs changing the semantics of address selection, and
> also creates inconsistency between how addresses may be selected
> between a connected and unconnected sockets. Consider that
> ip_local_out_sk calls netfilter NF_INET_LOCAL_OUT hook before
> dst->output, so then netfilter would start seeing packets with zero
> source address???
understood.
>
> A lot of design in the stack is predicated on inet_select_addr
> returning the source address to use for sending a packet. This should
> always return a reasonable address as an invariant, if someone wishes
> to rewrite addresses at a lower layer that's fine, but that should be
> defined as a NAT operation. If a device wants to weigh in on address
> selection then we can define an ndo function for that as I mentioned
> before.
I am floating an idea internally that re-implements how VRF impacts the
stack. It's 4.4 material and essentially adds dev_xxxx() / ndo functions
for the intrusions. With net-next closed no since throwing them out yet
and Nikolay always has good comments on my wild ass ideas.
David
next prev parent reply other threads:[~2015-09-10 1:10 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-09 21:57 [PATCH net-next 1/2] net: Refactor path selection in __ip_route_output_key David Ahern
2015-09-09 21:57 ` [PATCH 2/2 v2] net: Remove VRF change to udp_sendmsg David Ahern
2015-09-10 0:04 ` Tom Herbert
2015-09-10 0:23 ` David Ahern
2015-09-10 0:51 ` Tom Herbert
2015-09-10 1:10 ` David Ahern [this message]
2015-09-10 3:20 ` David Miller
2015-09-10 3:32 ` David Ahern
2015-09-09 22:56 ` [PATCH net-next 1/2] net: Refactor path selection in __ip_route_output_key David Ahern
2015-09-10 0:00 ` David Miller
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