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    Same subnet in radvd.conf with two different prefix lengths

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      tbclark3 last edited by

      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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