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random things and thoughts … and bad ideas

Monthly Archives: October 2014

dynamic prefix delegation can be easy

A few months ago I coincidently noticed my router having an IPv6 address. I knew my ISP was in the process of rolling out IPv6 but I never got or found any announcement that it was available for me. So I tried out setting up a prefix delegation for all my local networks. Sadly I noticed two things, which in hindsight might have been incorrect even back at that time. Firstly I was only able to receive a 64-bit prefix and secondly which made things appear even worse the prefix did not seem to be static. That meant I needed automatic delegation of the possibly changing prefix but could not use SLAAC and I couldn’t get any DHCPv6 client I tried to actually do a prefix delegation with prefixes longer than 64-bit. Probably because most people follow the suggestion to never use prefixes beyond 64 so I couldn’t find any usable reference how to get it to work. To my surprise some people even seem to think it is impossible to use prefixes longer than 64-bit at all. I just went on hacking together some ugly dhcpcd hook to manually apply the prefix from the DHCPv6 reply to the interfaces and change the dnsmasq configuration. My hack even worked to some extent. Some problems with randomly vanishing host addresses remained but I could not pin point the cause. Yesterday I tried reworking my setup to find the cause and again by total coincidence I came across a note that my ISP does in fact delegate 56-bit prefixes. Obviously with that info there was no more need for dirty hacks and I could try doing my delegation properly™.

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