Re: Correct behavior for IPv6 RA selection?

[Pavel Simerda <psimerda redhat com>]

Martin already replied to the bug report I created. I will further investigate the topic and will add information there. It will be a long run (even though the particular problem with multiple gateways might be solved soon).

Cheers,

Pavel

----- Original Message -----
> From: "Dan Williams" <dcbw redhat com>
> To: "Martin Jackson" <mhjacks swbell net>
> Cc: networkmanager-list gnome org
> Sent: Friday, January 25, 2013 4:31:28 PM
> Subject: Re: Correct behavior for IPv6 RA selection?
> 
> On Sat, 2013-01-19 at 10:38 -0600, Martin Jackson wrote:
> > I have several machines on a couple of different VLANs (same
> > physical
> > interface) doing IPv4 and IPv6 DHCP.  I have two vm's running
> > Quagga on
> > Ubuntu 12.10 doing router advertisements with different preferences
> > set.
> > (Host 741e is advertising a "high" preference RA, b6dc is offering
> > "medium" preference).
> > 
> > I see that recently there was an issue and a fix for n-m making
> > cache
> > routes permanent in the IPv6 routing table on the client.  I
> > believe
> > there may also be an issue with n-m creating a static route in the
> > presence of multiple devices advertising RAs.
> > 
> > I have Windows 7, Ubuntu 12.10 (with n-m), Fedora 18 (with n-m).
> > 
> > My question relates to the "static metric 1" route to one of these
> > routers.  I believe that it is incorrect for n-m to add this, as
> > this
> > static route does not disappear when its advertising router goes
> > away,
> > and hinders failover to the surviving router.
> 
> This behavior is currently expected, but your point is well taken and
> the current behavior should be changed to ensure that failover with
> multiple IPv6 routers on the same link is not broken.  We'll need a
> bit
> more developer discussion on whether NM should be adding static
> routes
> for each router (with the appropriate metric based on which interface
> NM
> sets as default/primary) or something else.
> 
> The reason NM adds a static default route is for the case of multiple
> connected IPv6 interfaces.  The two interfaces may be connected to
> different networks, and those two networks are unlikely to be
> coordinated, and so the RAs may have similar or conflicting
> priorities.
> In this situation, NM can automatically pick an interface as the
> "default" one, or the user can override this choice with "Only use
> this
> connection for resources on its network" in which case NM should
> ensure
> that there is *no* default route on that interface, even if the
> router
> says it should be one.  Which would imply deleting the
> kernel-provided
> default routes or ensuring the kernel doesn't add them (because the
> user
> asked NM to).
> 
> Dan
> 
> > Here is my IPv6 route table from one of my Ubuntu clients:
> > 
> > 2001:470:79::14:123 via fe80::5054:ff:fe9c:741e dev wlan0  proto
> > static
> > metric 1024
> > 2001:470:bd11:4::2749:6f83 dev wlan0  proto kernel  metric 256
> > 2001:470:bd11:4::/64 dev wlan0  proto kernel  metric 256  expires
> > 2592321sec
> > 2001:470:d8d3:1::1 via fe80::5054:ff:fe9c:741e dev wlan0  proto
> > static
> > metric 1024
> > 2600:3c03::f03c:91ff:fedf:9b84 via fe80::5054:ff:fe9c:741e dev
> > wlan0
> > proto static  metric 1024
> > 2607:f0d0:2001:de::add via fe80::5054:ff:fe9c:741e dev wlan0  proto
> > static  metric 1024
> > fe80::/64 dev wlan0  proto kernel  metric 256
> > default via fe80::5054:ff:fe64:aad0 dev wlan0  proto static  metric
> > 1
> > default via fe80::5054:ff:fe64:aad0 dev wlan0  proto kernel  metric
> > 1024
> > expires 2sec
> > default via fe80::5054:ff:fe9c:741e dev wlan0  proto kernel  metric
> > 1024
> > expires 9sec
> > 
> > 
> > Here is my IPv6 route table from my Fedora 18 client:
> > 
> > 2001:470:bd11:5::2884:2eff dev eth0  proto kernel  metric 256
> > 2001:470:bd11:5::/64 dev eth0  proto kernel  metric 256  expires
> > 2591995sec
> > fe80::/64 dev eth0  proto kernel  metric 256
> > default via fe80::5054:ff:fe01:b6dc dev eth0  proto static  metric
> > 1
> > default via fe80::5054:ff:fe01:b6dc dev eth0  proto ra  metric 1024
> > expires 7sec
> > default via fe80::5054:ff:fe2f:62c2 dev eth0  proto ra  metric 1024
> > expires 4sec
> > 
> > Finally, here is the route table from my non-nm Ubuntu raring
> > client.  I
> > believe this displays the correct behavior:
> > 
> > 2001:470:bd11:5::/64 dev eth0  proto kernel  metric 256  expires
> > 2591993sec
> > fe80::/64 dev eth0  proto kernel  metric 256
> > default via fe80::5054:ff:fe01:b6dc dev eth0  proto ra  metric 1024
> > expires 5sec
> > default via fe80::5054:ff:fe2f:62c2 dev eth0  proto ra  metric 1024
> > expires 2sec
> > 
> > The windows client does not add a static route, and also shows
> > different
> > metrics (preferring the router with the higher advertised
> > preference).
> > 
> > I am open to the idea that I am incorrect about how the kernel and
> > n-m
> > should handle IPv6 default routes, but I believe the addition of
> > the
> > static route is a bug in n-m.  Since v6 is kind of new, and since I
> > can
> > observe this behavior in two different distributions, I thought it
> > might
> > be worthwhile to bring it up on this list to see if it is really
> > that
> > clear-cut.
> > 
> > Thanks,
> > 
> 
> 
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