[Dnsmasq-discuss] Adding Route Information Option to prefixes in RA

[Steven Barth]

Hi Simon,

just stumbled upon this and wanted to add some notes about that because 
I have some experience with RIOs from OpenWrt already. If you want to 
send RIOs because you want to be compliant with RFC 6204/7084 you should 
send them with the prefix that was delegated to the router running 
dnsmasq not the prefix that was actually assigned to the interface (i.e. 
if you get a /56 from the ISP you should announce the /56 as RIO and a 
/64 out of that as PIO to make it work).

In addition and what is probably more critical here: some client 
implementations don't handle PIOs and RIOs for the same prefix very well 
(at least with the most-common prefix-size of /64 that is) and it might 
in some extreme cases even lead to disrupted connectivity between hosts.
Since I had the fun to debug such a case and want to spare you the 
trouble you might want to have a look at this lengthy thread: 
https://dev.openwrt.org/ticket/17396


Cheers,

Steven