DHCPv6 Prefix Delegation reject with code NotOnLink

[Alain Pieters]

All,

consulting the pool of experts here for an ipv6 issue with my ISP - Carl is the man I need here 😉

My router is asking the telenet cable modem for an IPv6 address via DHCP and is also adding the IPv6 prefix delegation option in the SOLICIT:

(BTW I tried all prefix lengths: from /64  up to /48)

The ADVERTISE from the cable modem is showing that it can not fullfil the PD request from my router:

 

RFC8415 is indicating that a client receiving a notonlink status should ignore that message... Hence no prefix for the router. 

The rest of DHCPv6 process continues (request/reply) so my router ends up with an IPv6 address on his WAN link towards the cable modem but all my host on the LAN are left on IPv4...

Telenet model= compal CH7465LG-TN.

Full packet trace of DHCPv6 communitication can be unicasted if desired.

Any idea what is going wrong here?

Many thanks,

Alain

[Wuyts Carl]

Of course Alain.

Our Telenet modems are, by default, routers as well as modems, so on top of the modulation/demodulation  they are also the L3 point in your home network. (including nat, firewall, …)

 

In the past, some attempts were done for supporting router-behind router, first via hipnet, later homenet, but never got standardized, or at least nowhere inplemented really.

We did implement the hipnet flavor many years ago, still under the control of Hans Thienpondt back then, but in the end, this is fixing the v6 part for router behind router, but keeps doing double NAT for IPv4, so not really a good solution.  This however can still be used on older modems, but is no longer present on newer ones.

We however do have an exception to that as you can use the CV8560E model for this.  This has an option to be put in “bridged” mode, although this is MacPAssThrough rather than bridge.  This will give you a pubic IPv4 address on your own router behind the Telenet modem (only 1 router allowed) and the IPv4 traffic gets bridged through the modem.

For the IPv6 part, it will sub-delegate a part of the received /56 on the WAN of the Telenet modem, and assign this part (today a /60, should become later probably a /57 (as big as possible)) to your own router via the ia_pd option, hence fully supporting the router behind router, while keeping all legacy devices, like older STBs etc, working as intended.

 

Hopes this answers your question, if not, I’m sure more q’s will follow 😊.

During last IPv6 council, Eric also pointed out that IETF is working on something in this area.

 

Regs

Carl

 

 

 

From: belgianv...@ipv6forum.com <belgianv...@ipv6forum.com> On Behalf Of Alain Pieters
Sent: Wednesday, January 24, 2024 10:09 AM
To: belgianv...@ipv6forum.com
Subject: [Belgian IPv6 Council] DHCPv6 Prefix Delegation reject with code NotOnLink

 

U ontvangt niet vaak e-mail van apieters...@gmail.com. Meer informatie over waarom dit belangrijk is

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