Linux and ULA support and default route

Jeroen Massar jeroen at
Thu Oct 13 10:27:21 CEST 2016

On 2016-10-13 09:36, Tore Anderson wrote:
> * Jeroen Massar <jeroen at>
>> 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.
> Not if you set the accept_ra_rt_info_max_plen sysctl to >= 48 (and the
> router implements RFC 7084 L-3).

Which is why looking at the exact RA is important.

> As far as I know, this sysctl is 0 by
> default which causes the kernel to ignore RIOs.

Correct. See among st others here for reasoning:

and as it is default 0, unless one does already salt/puppet/etc to
change that default, it won't easily get deployed; and if one does
salt/puppet/etc then adding static routes can also work.

Much easier and better to let the actual routers decide on routing
though and not end-hosts.

> I believe that Windows do accept RIOs by default so that's probably why
> it worked for Brian. NetworkManager user-space RA processing will also
> respect RIOs by default.

Only silly people run broken software like "NetworkManager" ;)


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