netdev - Re: forwarding of ipv4 link local addresses

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Message-ID: <20151209134416.GB11201@pox.localdomain>
Date:	Wed, 9 Dec 2015 14:44:16 +0100
From:	Thomas Graf <tgraf@...g.ch>
To:	David Miller <davem@...emloft.net>
Cc:	dsa@...ulusnetworks.com, netdev@...r.kernel.org
Subject: Re: forwarding of ipv4 link local addresses

On 12/03/15 at 02:35pm, David Miller wrote:
> From: David Ahern <dsa@...ulusnetworks.com>
> Date: Tue, 1 Dec 2015 13:35:58 -0800
> 
> > RFC 3927 states that packets from/to IPv4 link-local addresses
> > (169.254/16) should not be forwarded, yet the Linux networking stack
> > happily forwards them. Before sending in a patch I wanted to inquire
> > if this behavior is intentional.
> 
> It probably won't break anything if we prohibit this, so sure send
> a patch.

I don't have the full email context so apologies if this is not
relevant. The RFC states that such addresses should not be forwarded
_beyond the local link_. So as long as you are not breaking forwarding
of these addresses on the local host, I'm perfectly fine.

I bring this up specifically because of:

commit d0daebc3d622f95db181601cb0c4a0781f74f758
Author: Thomas Graf <tgraf@...g.ch>
Date:   Tue Jun 12 00:44:01 2012 +0000

    ipv4: Add interface option to enable routing of 127.0.0.0/8
    
    Routing of 127/8 is tradtionally forbidden, we consider
    packets from that address block martian when routing and do
    not process corresponding ARP requests.

    [...]

This feature is being used by a popular PaaS which leverages the
127/8 address space locally without polluting an entire routeable
address space.
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