IPv6, multihoming, and customer allocations

Owen DeLong owen at delong.com
Sun Mar 14 01:49:58 CST 2010

On Mar 13, 2010, at 9:49 PM, Rick Ernst wrote:

> A couple of different incantations searching the archive didn't  
> enlighten
> me, and I find it hard to believe this hasn't been discussed.   
> Apologies and
> a request for pointers if I'm rehashing an old question.
Don't have the pointers handy, but, it has been discussed as well as the
meta-discussion of the general lack of BCP and documentation available.

One good source for some information is http://www.getipv6.info

> As a small/regional ISP, we got our /32 assigned and it's time to  
> start
> moving forward (customers are asking for it).  New hardware, updated  
> IOS,
> etc. are in the pipe.  Discussions are beginning with our upstream  
> providers
> for peering.  Now, what do we do?
Glad to hear customers are asking for it.  That's a good sign.

I think the next step is to start planning your address utilization.

Some ISPs are giving all customers a /48. Some are giving small  
SOHO, and small business) a /56 by default and a /48 on request. A /48  
given to each site of medium-to-large businesses, more with proper  

> A /48 seems to be the standard end-user/multi-homed customer  
> allocation and
> is the minimum allocation size from ARIN.  A /32 provides 65K /48s  
> so, in
> theory, we could give each of our customers a /48 and still have  
> room for
> growth.  A /48 also appears to be generally accepted as the the  
> longest
> prefix allowed through filters (although /49 through /54 are also
> discussed).  Most customers, however, won't be multi-homed.
Generally, that's pretty accurate.  Over time, I suspect the  
proportion of
multihomed customers will increase.

> Partly from an IPv4 scarcity perspective, and partly from general  
> efficiency
> and thrift, it seems awfully silly to hand out /48s to somebody that  
> may
> have a handful of servers or a couple of home machines, especially  
> with
> special addressing like link-local if the hosts are not expected to be
> internet reachable (back-end servervs, etc).
It isn't.  Repeat after me... IPv6 addressing is vast and was designed  
allow sparse allocations. It is not necessary to conserve every singe

> Based on the above, I'm looking to establish some initial policies  
> to save
> grief in the future:
> - /52 allocations to end-users (residential, soho, etc.)

/52 works, too, although most people who are doing less than /48 are  
to /56, with /48 as the fallback if /56 is not enough.

> - /48 allocations to those that request it

Good plan.

> - If you are going to multi-home, get your own space
Not necessarily.  There are still many multihoming scenarios that do not
meet the ARIN criteria for provider-independent address assignment.
As much as I would like to change the ARIN criteria, for now, the
community seems to feel that there is concern about overflowing the
capabilities of backbone routers if we did this.

> This is obviously a very broad brush and takes an insanely large  
> addressing
> model and makes it even larger (assigning /52s instead of /48s) but,  
> to me
> at least, it seems reasonable for a first-pass.
ARIN will accept you assigning anything up to  a /48 to any end user.   
over a /48 requires a justification.

> For context/scope, we currently have the equivalent of a bit more  
> than the
> equivalent of a  /16 (IPv4) in use.
Then your /32 may very likely be enough for you for IPv6.  Something  
to consider,
if you have multiple POPs or locations, you may want to enable  
of those locations on nibble boundaries.  Doing so means that you  
could do
16 POPs with a /36 each, or, 256 POPs with a /40 each.  Each of the  
16 /36
POPs would support roughly 4,000 customers. If you go to /40s, then, you
only get 200 customers per POP.

Hope this helps,


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