Sharing a single /64



  • I want to share a single /64 prefix with around 12 interfaces but I keep reading I should divide a /64 prefix any further, I tried it anyway but as it turns out /64 seems to be the smallest I can go in pfSense.

    Currently I use all of these interfaces because they have different policies, like traffic shaping, VPN gateways, etcetera.

    How can I set DHCPv6 for a portion of a /64 for each interface? Is it possible? Would I be able to isolate select interfaces so there's no inter-VLAN routing happening? I am completely lost.

    There are servers running on most interfaces so a managed network is a must.


  • LAYER 8 Netgate

    Get a /56 or a /48. Use /64s on the interfaces. It is not pfSense. It is IPv6.



  • Thanks, that's what I was afraid of. It's just a /64 is already huge. These IPv6 designers went overboard.

    Thanks again, I'll start deploying right away. 🤓


  • LAYER 8 Netgate

    Stop sweating it. Every network segment gets a /64. You never have to worry about interface subnet size again.


  • LAYER 8 Global Moderator

    Exactly.. Think of /64 as today you think of a /24 or smaller.. /64 is the prefix you put on an interface.. Be it your going to have 4 devices or 400 devices on this network its a /64 you would use.  Shoot even if was a point to point where you would normally use a /30 in ipv4 you would use a /64 in ipv6..

    Unlike say a /24 in ipv4 you would not subnet a /64 that is the smallest you go.. If you need more networks then you need a /60, /56 /48 etc..



  • I'm setting up HE.net and already got the /48 block; I have a doubt though, does the GIF interface stays the same or do I need to reconfigure it with the /48 info, or, does that go in the DHCP/RA section?

    Thanks for your help, again!


  • LAYER 8 Netgate

    the GIF stays the same. You assign /64s out of the /48. You have 65536 of them to play with.



  • Thanks, this is so cool. 😃 💾



  • @vitaprimo:

    Thanks, that's what I was afraid of. It's just a /64 is already huge. These IPv6 designers went overboard.

    Thanks again, I'll start deploying right away. 🤓

    It's not huge, compared to the IPv6 address space.  ISPs hand out /56 or /48 prefixes.  That's 256 or 65536 /64s.  That's still puny compared to what's available.  At the moment, only 1/8th of the entire IPv6 address space is assigned to global address use.  Over 3/4s is not assigned for anything.  Even then, there are enough /48s for every single person on earth to have over 4000 of them.  So, lets have no more of this nonsense about splitting a /64.

    Incidentally, a /64 contains the entire IPv4 address space squared!.



  • @Derelict:

    the GIF stays the same. You assign /64s out of the /48. You have 65536 of them to play with.

    Can pfSense assign the full /48, up to FFFF?  On my system, the prefix IDs only go up to FF.  But I only have a /56 prefix.


  • LAYER 8 Global Moderator

    Yeah 65K /64 pretty much enough for as many networks you would ever need to create even if you think of a /64 as overkill with the number of address that can be on it..  And if not then get a /32 ;) This can be a issue to get your head around for sure.. It takes a bit to forget your ipv4 thinking - to me /64 with how many addresses that can be on it seems so wasteful..  But in the big picture with how big ipv6 space it really is almost infinite… Which I am sure that is what they thought of the ipv4 space when they started - and look how that turned out..

    But compared to how much space there is on ipv4, ipv6 is so freaking big!!! I mean big!!! that while using a /64 for a couple of devices might seem wasteful - that is how its designed, and there will never be an issue for IP addresses - not for your great grandkids for sure even ;)  If not great great great, etc..


  • LAYER 8 Netgate

    You need a /48 to delegate /56 to other sites which is as small as anyone should go. You need a /56 to delegate /60.



  • And if not then get a /32 ;) This can be a issue to get your head around for sure.

    There are enough IPv6 Global Unicast Addresses to give everyone on earth a /36 and have lots left over!

    But in the big picture with how big ipv6 space it really is almost infinite… Which I am sure that is what they thought of the ipv4 space when they started - and look how that turned out..

    According to Vint Cerf, one of the creators of the Internet.  IPv4, with 32 bit addresses, was just intended to be a proof of concept, with the real version having a much larger address space.  Unfortunately, it escaped.


  • LAYER 8 Netgate

    Can pfSense assign the full /48, up to FFFF?  On my system, the prefix IDs only go up to FF.  But I only have a /56 prefix.

    If you get a /48 PD you can set the track interface prefix ID from 0 to ffff. What is displayed and accepted as input there is dynamic and is dependent on the size of the PD. (A /60 shows 0 - f)

    pfSense running with thousands of defined interfaces is another matter.


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