BCP: Slicing a /32 for an ISP

Jeroen Massar jeroen at unfix.org
Mon Apr 14 15:39:14 CEST 2008

Steve Bertrand wrote:
> Quick to the point:
> Has anyone done any documentation on how they decided to slice up their 
> IPv6 allocation?
> I'm pulling hairs deciding on a tactical solution for the long-term in 
> regards to how I should 'cut up' my /32.

Now, I unfortunately have to be a bit nasty again but.... (generally 
targeting people to maybe wake them up a little bit, hopefully they read 
this nasty comment before requesting... ;)

I do hope that you know how large a /32 is and how many customers you 
could potentially serve with it?

I also hope that you made an actual allocation plan and passed that in 
when you are going to request or when you requested your prefix from 
your favorite RIR.

Because, if you 'simply requested a /32' without doing the math, there 
are a few number of possibilities:
  - you where lucky
     - you will never have more than 65k customers

  - you made a mistake
     - you already have more than 65k customers
     - you will have more than 65k customers in a few years
     - you will force your customers and give them only a /128
       even though $RIRs allocate you space based on /48's
       (or /56 optionally in ARIN land)

Just asking though... as it seems a lot of ISP's are 'simply requesting 
a /32' while they actually don't have a clue on what a /32 is and how 
little amount of space that actually is.

Funny thing is that they then are like "but a /20 is hugeeee" for such a 
little ISP like D-TAG/France Telecom etc, forgetting that they simply 
plan ahead over the next couple of decennia and that they don't want to 
bother with renumbering during that period.

It would be really awesome if people who request a /32 actually did 
their work properly and calculated how much space they really need.
"simply requesting a /32' is not the way to go and it will bite you at 
one point or another. I'd really hate to see that an ISP goes back to an 
RIR and is like "yeah we kinda like don't fit in a /32, can you give us 
more" and then they go also like "yeah a /20 is good, but we won't 
return the /32 as we can't renumber from that"

Thus please people requesting prefixes, make a plan first and don't just 
do it for the next year. Ask here if wanted, there are a lot of people 
(also who are not as nasty as me ;) who can help out there in making the 
right decision.

Just like a lot of other things: when you have a question: ask the right 
question and you will receive the right answer. Aka: be verbose.


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