"src" attribute ignored for IPv6 (preferred source address selection)

"src" attribute ignored for IPv6 (preferred source address selection)

[Xavier Roche]

Hi folks,

In an attempt to change the source address in various conditions 
(network prefix, outgoing protocol, user owner id, ..), it appeared that 
the src attribute of an IPv6 route command (ip -6 route add .. src ..) 
was simply ignored.

The outgoing interface can be selected, but not the preferred source 
address (see (1)), which remains always the same within an interface.

If this a bug ? Or a known limitation of the kernel ?


(1) IPROUTE2 Utility Suite Howto
"src ADDRESS --- the source address to prefer using when sending to the 
destinations covered by route prefix. This address must be defined on a 
local machine interface. This will come into play when routes and rules 
are combined with the masquerade rules of the ipchains firewall we 
discuss later."

Re: "src" attribute ignored for IPv6 (preferred source address selection)

[Daniel Roesen]

On Sat, Sep 04, 2010 at 11:47:52AM +0200, Xavier Roche wrote:
> In an attempt to change the source address in various conditions (network 
> prefix, outgoing protocol, user owner id, ..), it appeared that the src 
> attribute of an IPv6 route command (ip -6 route add .. src ..) was simply 
> ignored.
>
> The outgoing interface can be selected, but not the preferred source 
> address (see (1)), which remains always the same within an interface.
>
> If this a bug ? Or a known limitation of the kernel ?

Well, at least it was a known limitation six years ago, when I
discovered the same:

http://lkml.indiana.edu/hypermail/linux/kernel/0409.0/1768.html

Unfortunately I don't have the time (and most probably not the necessary
kernel knowhow) to hack this up myself, but I'm still interested. :-)

Best regards,
Daniel

-- 
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Re: "src" attribute ignored for IPv6 (preferred source address selection)

[David Miller]

From: Daniel Roesen <dr@cluenet.de>
Date: Sun, 17 Oct 2010 03:12:08 +0200

> http://lkml.indiana.edu/hypermail/linux/kernel/0409.0/1768.html
> 
> Unfortunately I don't have the time (and most probably not the necessary
> kernel knowhow) to hack this up myself, but I'm still interested. :-)

The routing table in ipv6 can very much handle routing by source
address now, if the ip commands mention do not work it's some
bug in the tool or the routing table rule adding code in the
kernel.

It's not a fundamental limitation any more.