IPv6 reverse zones advise

Mark Andrews marka at isc.org
Mon May 10 23:58:16 UTC 2010

In message <20100510124432.19374b1xzk3abe0w at webmail2.ukgrid.net>, a.smith at ukgri
d.net writes:
> Hi,
>    we will shortly start using IPv6 reverse DNS, and having never used  
> it before I thought Id ask those with some experience if they have any  
> words of wisdom before I make any horrible mistakes ;) Ive already had  
> a good read of a good many sites on the subject but still would like  
> to check a couple of things.
> When creating IPv6 reverse zones can the subnet be as large or small  
> as you like? Ive seen examples using /48 and /64, can this be  
> effectively whatever you want?
> And following on from that if it is user definable, what would be the  
> recommended way (size) forward? We are using flat file zone files. To  
> me the simplest would seem to create the zones using large subnets and  
> where necessary (as occasionally we are asked to do) delegate via the  
> zone file some ranges to other DNS servers.
> Im not an expert in all of this really, but we get by on IPv4 so if  
> anyone has any tips they would be greatfully recieved,
> thanks Andy.

The answer to that lies in who (or what) is doing the updating.
This is a administative issue not a technical one.

For home being allocated a /56 I would not subdivide it.

For companies with different division on different subnets I would
subdivide the /48.  Also company zones tend to have more records
in them.

Whatever you do I would be consistent.  If you need to split out a
/64 for one subnet I would do it for all subnets even though it
means a little more work initially.

In my previous job I had a /16 (IPv4) and it was further sub divided
into /20's (one for each division in the state).  I delegate all
16 reverse zones at that point.  For IPv6 that would be a /48 and
delegating /52 which could be further sub delegated if needed at
the /64 boundary.  Note there would be a single delagation for the
/52 as it is at a nibble break point.

Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org

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