Re: [DNSOP] WGLC: "Considerations for the use of DNS Reverse Mapping"

On 1 Apr 2008, at 16:36 , Andrew Sullivan wrote:

> On Tue, Apr 01, 2008 at 10:36:28AM -0400, Edward Lewis wrote:
>
>> Multiple PTR records can be stored in a single PTR RRset.  If a
>> device at an IP address (v4 or v6) has multiple identities with
>> domain names, it would be good to have a PTR for each.  However, this
>> is not always practical.  In some operational situations, an address
>> may have thousands of domain names holding an address record (A or
>> AAAA) with the address as the value.

How about re-writing the last sentence as "In some operational  
situations, a single address might be used as RDATA for a large number  
of A or AAAA resource records."

>> The number of address records in an PTR set before tripping the upper
>> limit on what can fit on even a TCP carried DNS message is
>> approximately 4000 for A RR only and about 2000 for AAAA RR only.

"The maximum size of a DNS message is 65536 bytes [RFC1035]. The  
number of resource records in a single PTR RRset is correspondingly  
limited."

(The limit is surely a function of the average encoded size of RDATA  
for the PTR records in the RRset, and has nothing to do with whether  
the PTR record lives under in-addr.arpa or ip6.arpa?)

>> If an address has just a few corresponding forward map records, it is
>> worth entering them all. If an address has many, a better strategy is
>> to enter a few as is needed, adding more only when there is an
>> operational request.

I don't see value in adding the text above.

Joe

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