classless delegation

Re: classless delegation

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On 04/23/02 at 09:38, Mauro Ferrari wrote:

> I've read the thread on class c delegation started march12 by Alan,
> which was very helpfull for understanding delegation, but I can't
> find a way to check if the lame delegation I get when using DNSExpert
> on my DNS, is due to a bad or non existing delegation for my 5 IP's I
> own by my ISP.

'Lame delegation' means that authority for a zone has been delegated to a
name server which does not actually have authoritative data for it. I.e.,
the server in question does not have a local zone file for the zone. To
check a lame delegation, you would trace the delegation (NS) records,
starting from the root servers, and query each delegated server for data in
the zone. If one of the delegated servers returns a non-authoritative
response, then the delegation to it is lame. To fix it, you would need to
get the server set up as either a master or slave server for the zone.

> 1. Reverse lookups for my 5 Ip's are correct.
>
> 2. Is it possible to have just 5 IP's delegated to you for whom
> you're authoritive?
> A NS lookup on one of my IP's gives the following result:
>
> Non-authoritative answer:
> 155.3.2.1.in-addr.arpa PTR 85099 ns1.mydomain.com
>
> Authority:
> 3.2.1.in-addr.arpa NS 368160 dns1.myISP.com 1.2.4.9
> 3.2.1.in-addr.arpa NS 368160 dns2.myISP.com 1.2.4.10

Looks more like a PTR look-up to me, but I guess you meant nslookup. :-P

> Does this mean that I'm not authoritive for that number?

Maybe, but you haven't given us enough information. Was the above response
returned by your name server? Whatever server sent the response does not
have authoritative data for the 3.2.1.in-addr.arpa. zone. Also the
Authority section of the response indicates that dns1.myISP.com and
dns2.myISP.com are the only servers to which authority has been delegated.

> 3. If it's possible to delegate just 5 numbers, what's the easiest
> way for them, to set up classless delegation?

They would delegate a sub-zone of the enclosing Class C block to you:

a-e.3.2.1.in-addr.arpa. NS ns.your.domain.
a-e.3.2.1.in-addr.arpa. NS another.name.server. ; a secondary...

Then, in the 3.2.1.in-addr.arpa. zone, they'd replace the PTRs for your IPs
with CNAMEs pointing to records in the new sub-zone:

a.3.2.1.in-addr.arpa. CNAME a.a-e.in-addr.arpa.
b.3.2.1.in-addr.arpa. CNAME b.a-e.in-addr.arpa.
c.3.2.1.in-addr.arpa. CNAME c.a-e.in-addr.arpa.
d.3.2.1.in-addr.arpa. CNAME d.a-e.in-addr.arpa.
e.3.2.1.in-addr.arpa. CNAME e.a-e.in-addr.arpa.

On your name server, you would create a zone, a-e.in-addr.arpa., which
contains appropriate PTR records, corresponding to the CNAMEs in the parent
zone:

a.a-e.in-addr.arpa. PTR hosta.your.domain.
b.a-e.in-addr.arpa. PTR hostb.your.domain.
c.a-e.in-addr.arpa. PTR hostc.your.domain.
d.a-e.in-addr.arpa. PTR hostd.your.domain.
e.a-e.in-addr.arpa. PTR hoste.your.domain.

RFC 2317 describes this strategy in detail.

> Any input is appreciated!
>
> Mauro
>

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