netdev - Re: TCP using IPv4-mapped IPv6 address as source

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Date:   Wed, 11 Jan 2017 15:58:29 -0500
From:   Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "Jonathan T. Leighton" <jtleight@...l.edu>, netdev@...r.kernel.org,
        edumazet@...gle.com, Yuchung Cheng <ycheng@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>
Subject: Re: TCP using IPv4-mapped IPv6 address as source

On (01/11/17 12:43), Eric Dumazet wrote:
> 
> On Wed, 2017-01-11 at 14:59 -0500, Sowmini Varadhan wrote:
> 
> > I think the RFC states somewhere that you should never ever
> > send out a v4 mapped address on the wire.
> 
> Can you point the exact RFC ?
> 
> https://tools.ietf.org/html/rfc2765  seems to allow just that.

I have not read the details of 2765, but from a cursory look,
it talks about "IPv4-translatable addresses", not v4-mapped
addrs, and says,
"The address translation mechanisms for the stateless and the stateful
 translations are defined in [RFC6052]"
It's also not clear to me that 2765 warrants the use of these
as ip6 src, or ip6 dst, or the target(s) of NS/NA.

https://www.rfc-editor.org/rfc/rfc4038.txt refers to security
considerations about sending v4-mapped addrs on the wire
Looks like these security considerations are discussed in
 https://tools.ietf.org/html/draft-itojun-v6ops-v4mapped-harmful-02

In general, I think BSD and Solaris (and probably most
router implementations, esp the BSD-based ones) will not allow
v4 mapped addresses as src or dst of ip6 packets.

> Jonathan issue is about terminating such flows in TCP stack, which is
> likely not needed/useful.

sure. but if you configure the v4 mapped address as
a src addr "everything should be fine!"

--Sowmini