Re: DHCPv6 IA_PD - how-to

On 7/24/2024 04:10, Roy Marples wrote:
>   ---- On Wed, 24 Jul 2024 02:48:15 +0100  Karl Denninger  wrote ---
>   >     I'd like to replicate this that is currently being sent up via      dhcp6c, which is not quite-clear to me from the docs on how to do      that..
>   >     #
>   >       # This configuration will attempt to get /56 or a /60 from the
>   >       # ISP and assign a /64 internally.
>   >       # Note that if you have a /60 you can have four /64s defined; if      you have a
>   >       # /56 then obviously you can have 16 internal networks.  For most      "house"
>   >       # size networks four separate delineations is enough, for most      "moderate"
>   >       # sized corporate environments 16 is enough.  BE AWARE THAT THE      SLA-LEN MUST
>   >       # MATCH THE DIFFERENCE BETWEEN THE LOCAL PREFIX AND THE REMOTE      ONE!  If
>   >       # you ask for a /56 then sla-len is 8, if you ask for a /60 then      the sla-len
>   >       # is 4 (difference between the requested prefix length and 64,      respectively.)
>   >       #
>   >
>   >       interface igb0 {
>   >            send ia-pd 1;
>   >            send ia-na 1;
>   >            send rapid-commit;
>   >            script "/usr/local/etc/dhcp6c.script";
>   >       };
>   >
>   >       id-assoc na 1 {
>   >
>   >       };
>   >
>   >       id-assoc pd 1 {
>   >         prefix ::/56 1800;
>   >
>   >         prefix-interface igb1 {
>   >           sla-id 0;
>   >           sla-len 8;
>   >         };
>   >
>   >       };
>   >
>   >     igb1 is the "normal" internal network; igb0 is the external one.
>   >     The ISP hands out /56s (although at one time I could choose      either a /56 or /60); I have routines in the script file that then      generate dynamic updates for DNS so the gateway has its pointers      updated if/when the address changes (I run my own zones)
>   >
>   >     Its not entirely-clear how to replicate that in the config file for dhcpcd; I can figure out the script I'm sure, but the base config is not clear to me.
>
> So you would add this to the bottom of the default dhcpcd.conf file:
>
> interface igb0
>    ia_na
>    ia_pd 0/::/56 igb1/0/64
>
> That mirrors your config exactly apart from requesting a specific lifetime which dhcpcd doesn't support for PD.
> rapid commit is enabled already in the default dhcpcd.conf file.
> You could then edit /etc/dhcpcd.exit-hook to handle your DDNS.
>
> You might be able to get away with this lighter config as well, based on what you said:
> interface igb0
>    ia_na
>    ia_pd 0 igb1
>
> Any pointers on now to make this more clear in dhcpcd.conf(5) are welcome.
> Good luck!
>
> Roy

The provided example (starting with "noipv6rs") requests multiple 
prefixes and starts with "ia_pd 2"; what wasn't clear is the most-common 
example for a single-attached endpoint that might have multiple internal 
interfaces (e.g. separated subnets; perhaps one for a guest network or 
similar, another for general use, etc.)

Most installations whether personal or small/modest-size business on a 
per-location basis anyway likely have one external connection to the 
internet as a whole, point default at their ISP and expect them to hand 
them their DNS pointers as well. Some folks only need SLACC of course as 
their ISP-provided router does all this (e.g. many people on cable modem 
service these days where their modem is also a WiFi AP and router) but 
some (like myself) prefer to do that ourselves both for isolation and 
firewalling purposes. Most ISPs appear to hand out a /56 (some will go 
longer, but few shorter) even at the individual "personal, household" 
connection level so I'd bet that as a "sample" configuration in the 
manual would suit 90%+ of the users.


-- 
Karl Denninger
karl@denninger.net
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