Same subnet in radvd.conf with two different prefix lengths



  • I am getting a /56 from Comcast on WAN, and have LAN configured to track WAN.  It appears to me that Comcast is actually providing a /59 because the LAN address is a /59 even though I requested a /64.  This causes radvd to advertise the correct subnet but with a /59 length.  Many Linux clients won't accept a /59, so I added the same subnet on the RA services configuration page with a /64 length.  The /64 got added to radvd.conf in addition to the /59, resulting in the following:

    interface wlp3s0
    {
    AdvSendAdvert on;

    Note: {Min,Max}RtrAdvInterval cannot be obtained with radvdump

    AdvManagedFlag off;
    AdvOtherConfigFlag off;
    AdvReachableTime 0;
    AdvRetransTimer 0;
    AdvCurHopLimit 64;
    AdvDefaultLifetime 60;
    AdvHomeAgentFlag off;
    AdvDefaultPreference medium;
    AdvLinkMTU 1500;
    AdvSourceLLAddress on;

    prefix 2603:3023:31b:dbc0::/59
    {
    AdvValidLifetime 86400;
    AdvPreferredLifetime 14400;
    AdvOnLink on;
    AdvAutonomous on;
    AdvRouterAddr on;
    }; # End of prefix definition

    prefix 2603:3023:31b:dbc0::/64
    {
    AdvValidLifetime 86400;
    AdvPreferredLifetime 14400;
    AdvOnLink on;
    AdvAutonomous on;
    AdvRouterAddr on;
    }; # End of prefix definition

    route ::/0
    {
    AdvRoutePreference medium;
    AdvRouteLifetime 60;
    }; # End of route definition

    RDNSS 2603:3023:31b:dbc0:225:90ff:fe87:21f9 2603:3023:31b:dbc0:ec4:7aff:fe97:e468
    {
    AdvRDNSSLifetime 20;
    }; # End of RDNSS definition

    DNSSL ferree-clark.org ferree-clark.org
    {
    AdvDNSSLLifetime 20;
    }; # End of DNSSL definition

    My understanding is that radvd shouldn't advertise anything less than a /64–and, in fact, it is causing a string of errors:
    May 17 17:41:17 radvd 28044 prefix length should be 64 for igb1

    I am working around it by running a cron job once a minute to correct the radvd.conf file if it is incorrect.

    There must be a way to configure radvd to correctly advertise a /64 even though Comcast is giving us a /59, but I can't figure out what it is.

    Can anybody help?


 

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