firstly, like someone else said, its for a bit of structure, so that the
necessary people can see in what region the IP is in.
secondly, yes normally unused IPs have dns entries, especially for dial-up
users and DSL users. an isp i worked at previously have
modem1.ispname.co.za to modem99.ispname.co.za, so that when users dialled
up (seeing as DSL "dials" to some extent), they would have a hostname.
just because an IP resolves to a hostname, doesn't mean its in use, heck,
these days with security being such an issue, pinging a host and not
getting a reply doesn't mean the host is down, just means ICMP replies
aren't finding their way back to you. a lot of larger companies (from
what i've seen/experienced in .za anyway) & universities use DHCP for
workstations, and if they were handing out public IPs, chances are they'ld
have some sort of DNSing in place, so might as well allocate IP's
z.z.z.a-z.z.z.b for example once off.
in the case of a larger company/varsity, i'm sure they too would have
seperate scopes for each dept. for admin purposes.
On Thu, 31 Jul 2003, Terry wrote:
> Hi,
>
> I've googled but haven't really come across anything that answers my
> questions. Is it common practice for ISPs to allocate a block of
> addresses to a customer and put in DNS records for ones that are
> unused?
>
> For example, xxx.8-xxx.15 is assigned to the customer. Customer uses
> xxx.9 for the router and xxx.10 for web server. xxx.11-14 are unused.
> I would expect to see DNS records for xxx.9 and xxx.10 but not for the
> rest of the block. Am I wrong? If there are DNS records for the rest
> of the IPs, why is that? Is there some security reason for doing
> this?
>
> --
> Regards,
> Terry
>
>
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>
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Received on Aug 01 2003
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