DHCPv6 DNS Listing With Prefix from ISP that is not Static



  • Hi all,

    I'm trying to determine the correctly way to advertise an ipv6 address for my DNS server. I have assigned the DNS server a static ip via dhcpv6 static mapping. However, it appears the prefix my ISP gives me for can change. This creates a problem when trying to put a static entry in place for listing a DNS server ipv6 address with DHCPv6 (because at some point, that ip will change).

    Is there a way to make this work? With openwrt, when putting in a dhcpv6 reservation, it would assign the same static mapping (suffix) on the ISP prefix (GLA) and the ULA address. However, in my attempt to setup ULAs with pfsense, it appears that the static mapping suffix did not apply to the ULA, only the GLA.

    Any help would be appreciated.



  • There's a setting about not releasing the prefix. If that isn't selected, pfSense may get a new prefix for something as minor as disconnecting/reconnecting the WAN cable.Which version of pfSense are you running? Earlier versions didn't have that setting.



  • Ahhh... I didn't think about that. Are you referring to "Do not allow PD/Address release"? I'm on the latest pfsense.

    Are prefixes typically pretty stable once this is enabled or does it depend on ISP?



  • That's it. Make sure it's selected. I can't say the addresses will never change, but they are stable.



  • How stable it will be depends largely on your ISP and their expiration of delegated prefixes. My ISP has an expiration period of 7 days, so as long as I'm not offline for more than a week, I should maintain the same prefix. Of course the only times I'm offline are when they're doing maintenance, so it's rare that it changes. It's been the same for over a year (along with my IPv4 WAN address).

    An ISP with a much shorter expiration period, though, could prompt a prefix change if you're offline that long.



  • @virgiliomi

    I've had the same prefix since that setting was added, about 2 years ago IIRC. That's stable enough for me. On IPv4, my host name is based on firewall & cable modem MAC addresses and so never changes unless I change hardware. This means that no matter what my IPv4 address is, I can still find my network. However, my IPv4 address is also stable, so long as I leave my firewall running, other than the rare occasion when my ISP makes network changes.