North American Network Operators Group

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Re: v6 subnet size for DSL & leased line customers

  • From: Chris Adams
  • Date: Fri Dec 21 12:23:46 2007

Once upon a time, TJ <[email protected]> said:
> Short answer - no spec for it.
> 	ARIN breaks it at /56, as a nod towards maybe a /48 for everyone is
> a bit much.

On ARIN's site:

 The following guidelines may be useful (but they are only guidelines):

    * /64 when it is known that one and only one subnet is needed
    * /56 for small sites, those expected to need only a few subnets
      over the next 5 years.
    * /48 for larger sites

 For end sites to whom reverse DNS will be delegated, the LIR/ISP should
 consider making an assignment on a nibble (4-bit) boundary to simplify
 reverse lookup delegation.

So, the guidelines are on 8 bit boundaries, but then right below they
also suggest making assignments on 4 bit boundaries (and it is all "only

Chris Adams <[email protected]>
Systems and Network Administrator - HiWAAY Internet Services
I don't speak for anybody but myself - that's enough trouble.