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I'm a complete noob at IPv6, but have some practical experience of IPv4 (just because I had to deal with it).
My home router is behind CGNAT so they don't offer public IPv4 addresses, but I'd asked about getting an IPv6 address and my ISP has kindly provided me with one. In their reply they said my address is 2a01:XXXX:XXXX:4000::/56
. Reading about it, I got the idea that I can and should provide my network devices with GUAs which is kind of appealing to me.
Behind my ISP's router I've got a OpenWRT one for educational purposes. All my other devices are behind the latter. In order to properly run DHCP my OpenWRT needs to get a prefix from my ISP's router (that is DHCPv6 enabled as well).
My confusion comes about the /56
at the end of the address. I guess network masks don't make sense for GUAs so is that the delegated prefix that I can use for my private network? If so when assigning the prefix to my OpenWRT router should I narrow it down in case I decide to have more devices behind my ISP's router in the future?
How can I validate that the whole thing works as expected? My ISP's router has a crappy UI and no console, I can see the GUA having been assigned but not the /56
(which I won't put a name on because I'm not sure what it's called yet). My OpenWRT assigns addresses to hosts based on its global ULA settings which means its not taking into account whatever prefix the other router may be publishing (if it even works properly).
The ISP router has a checkbox to enable prefix delegation based on the WAN settings (which is checked) and another section for static prefixes which is empty atm.
It might be useful for you to read this related question. Something is not right in the information you got from the ISP. If they provide you with a global unicast address with a prefix length, then that's supposed to be the WAN link prefix which is supposed to be a
– kasperd – 2018-10-11T09:14:10.513/64
. A/56
is appropriate for a routed prefix, but then it should only have 56 bits specified in the prefix. Does the address look like2001:db8:39a3:bb00::/56
or like2001:db8:39a3:bb00::2/56
?Sorry I was sloppy in my question, their email stated they've assigned the
2a01:XXXX:XXXX:XXXX::/56
to my router, when I go on the router I can see the 128 bits address, which makes sense as this would be the interface address, whereas their would specify the assigned prefix (hopefully I'm using the right terminology here). Thanks! – marius-O – 2018-10-11T10:03:10.473The last two digits are important. There is a major difference between whether they wrote
2001:db8:39a3:bb00::/56
or2001:db8:39a3:bb3a::/56
. – kasperd – 2018-10-11T10:08:51.207That would be
2a01:XXXX:XXXX:4000::/56
– marius-O – 2018-10-11T10:14:58.9301That's a routed prefix. The two layers of routers make the configuration more complicated, but a
/56
is definitely enough to configure two layers of routers. I recommend routing a/60
from the outer router to the inner router. But before getting into that, I recommend getting the configuration working for devices connected directly to the outer router. A screenshot of the UI for the outer router may help understand how it is to be configured. – kasperd – 2018-10-11T10:23:33.453Sorry for the delay, here are some screenshot for my ISP router UI: http://screenshots.portforward.com/routers/ZTE/ZXHN_H298N_-_Hyperoptic/ with the relevant screens being http://screenshots.portforward.com/routers/ZTE/ZXHN_H298N_-_Hyperoptic/Prefix_Delegation.htm and http://screenshots.portforward.com/routers/ZTE/ZXHN_H298N_-_Hyperoptic/Static_Prefix.htm When I get back home I'll also post the IP address OpenWRT gets on its wan6 (if I remember correctly it's a
– marius-O – 2018-10-12T08:31:12.527/128
which means there's no delegation happening). Also devices connected directly into ISP router get IPv6 connectivity e2e