Rogers and changing prefix



  • I'm on Rogers and get IPv6 from them.  However, I've noticed the IPv6 prefix changes occasionally, either on it's own or if I disconnect/reconnect the cable modem.  However disconnecting doesn't always cause it to change and my prefix even survived changing modems.  My DUID hasn't changed since May 23 and I thought it's purpose was to ensure always getting the same prefix.  This seems to work, but not all the time.

    Has anyone else noticed this?

    tnx jk



  • Are you using permanent storage for pfSense, or are you using a RAMdisk? If the latter, there's a known issue as the DUID is stored in the RAMdisk filesystem, causing it to be deleted on a reboot of pfSense, thus a new prefix is assigned by your ISP.

    If the former, then there's no reason it should be changing all the time, unless your ISP is expiring the existing lease or just not allowing the same prefix to be renewed for whatever reason.



  • It's stored on the hard drive and it shows a file write date of May 23.



  • I'm not on Rogers, but it is quite possible the they are using generic ISP hardware/software, as I've seen similar behaviour with ISP's all over the globe, both in VDSL and Cable connections. Strangely enough, not with fiber connections, maybe they are using different equipment and a different backbone for addressing?

    Anyway, it seems that while prefixes are 'reserved', if you happen to be offline and some other client is requesting a prefix, it is possible that it gets "your" prefix, causing it to be out of the pool when you request it, and thus it gives you a different one. The idea behind my reasoning is that I can actually ping a at least 1 address within the prefix that I used to have, so I know someone on the other end is listening.



  • I am never off line.  My firewall/router is up 24/7.  There have been times when the prefix changed when all I did was momentarily disconnect it from the modem.  There have also been times when it just changed on it's own.  On the other hand, my prefix did survive swapping modems, with there being no modem at all for the time it took me to disconnected it, walk over to my ISPs local store, walk back and install the new modem.  Again, the whole point of the DUID is to keep the prefix from changing.  With this same ISP, my IPv4 address changes so seldom, it's virtually static.



  • @JKnott:

    I am never off line.  My firewall/router is up 24/7.  There have been times when the prefix changed when all I did was momentarily disconnect it from the modem.  There have also been times when it just changed on it's own.  On the other hand, my prefix did survive swapping modems, with there being no modem at all for the time it took me to disconnected it, walk over to my ISPs local store, walk back and install the new modem.  Again, the whole point of the DUID is to keep the prefix from changing.  With this same ISP, my IPv4 address changes so seldom, it's virtually static.

    Yeah, that's what the DUID is supposed to do, but it's very possible that the ISP has a broken IPv6 setup, or doesn't store the prefixes correctly. I've also had (but this was PPPoE based) situations where if you disconnect and quickly re-connect, the previous PPPoE session wasn't seen as disconnected by the ISP which then resulted in a completely different prefix getting sent down the line. This was also happening with IPv4, but in your case that doesn't seem to be.

    With most of the lines being business lines, it was easy for me to get that information, but on consumer lines, it's usually not easy to get any kind of information or spec from the company to understand why it's working (or not working) in a certain way. Have you called your ISP yet?



  • I called the support line and advised them.  They said IPv6 isn't officially supported yet, so there may still be issues.  They said they'd forward my probelm to the appropriate people.  Hopefully, it's just a teething problem that will be resolved shortly.  At least the person I was talking to knew what the DUID was and what it's supposed to do.


Log in to reply