Specifying IPv6 off-link for a subnet

Mel Pilgrim list_freebsd at bluerosetech.com
Mon Jul 19 19:40:45 UTC 2021

On 2021-07-18 17:07, Scott wrote:
> On Wed, Jul 07, 2021 at 07:43:48PM -0700, Mel Pilgrim wrote:
>> On 2021-07-05 8:45, Scott wrote:
>>> I have manually configured IPv6 on the interfaces:
>>> ifconfig_vmx0_ipv6="inet6 xx::yy prefer_source accept_rtadv -autoconf no_radr"
>>> Here's the received RA:
>>> 	  prefix info option (3), length 32 (4): xx::/64, Flags [none], valid
>>> 	  time 3600s, pref. time 60s
>>> Note that there is no L flag set, so the prefix is off-link.
>> If set, the L flag indicates the prefix can be used for on-link
>> determination. But if the L bit is unset, the PIO isn't making any
>> assertion about the prefix being on-link or off-link. More importantly,
>> a host must not use a PIO with L=0 to conclude a prefix is off-link.
>> IOW, it is correct for a host to do nothing when it receives an RA PIO
>> with no flags for an already-configured prefix.
> so for the case of manually addressed devices on a private vLAN/IPPL there
> must be a way to specify that the configured prefix is not on-Link.

Yes, by not configuring that prefix.  Numbering vmx0 into xx::/64 made 
xx::/64 on-link by definition.

This seems like too intuitive of an answer, though.  Can you step back 
and explain what you need to do at a higher level?

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