Linux and ULA support and default route

[Jeroen Massar]

On 2016-10-13 02:30, Brian E Carpenter wrote:
> Hi Jeroen,
> On 13/10/2016 12:16, Jeroen Massar wrote:
>> On 2016-10-13 00:51, Brian E Carpenter wrote:
>> [..]
>>> Kernel IPv6 routing table
>>> Destination                    Next Hop                   Flag Met Ref Use If
>>> fd00::/64                      fe80::be05:43ff:fe8e:ce39  UG   600 1    12 wlp2s0
>>> fe80::/64                      ::                         U    256 0     0 wlp2s0
>>> ::/0                           ::                         !n   -1  1   137 lo
>>> ::1/128                        ::                         Un   0   3     7 lo
>>> fd00::c5bb:40f2:f3d5:94e4/128  ::                         Un   0   3    19 lo
>>> fe80::9051:543a:4c9e:e93e/128  ::                         Un   0   2    11 lo
>>> ff00::/8                       ::                         U    256 2  1763 wlp2s0
>>> ::/0                           ::                         !n   -1  1   137 lo
>>
>> Do you receive those prefixes over RA or manual config?
> 
> RA of course
> 
>> Is forwarding enabled? 
> 
> No
> 
>> What does the ra_accept sysctl say?
> 
> accept_ra = 1
> 
>>
>> Also 'ip -6 ro get <prefix>' can be very useful to check where the
>> routing table thinks packets are supposed to go.
> 
> Well, once I create the default route it tells me exactly what it should,
> for any global-scope address. But after reboot it says "unreachable"
> for any address outside the ULA /64 (i.e. even the rest of the ULA /48
> is unreachable).

RA's only install the /64 and when default announced a default.

Thus 'the rest of the ULA /48' would require a default route to be
installed to reach that...

When the device does not install a default route, there won't be an
entry for anything in that /48, just the /64 and thus that space won't
be reachable.


Btw: IMHO ULAs are in 99% of the cases the wrong thing to use anyway.
But note, this is not specific to ULA at all. (Except maybe that your
device chose to not push a default route, as there is no default route
to the Internet).

You might want to check with tcpdump with the exact details of the RA are.

Greets,
 Jeroen