AS15541 CETI-AS CETI ISP, Poland

Seventeen of eighteen addresses answer, and the two exceptions sit on a different domain.

What it's used for

• A regional internet provider. Twelve IPv4 prefixes announced from Poland, no IPv6, four and a half thousand addresses, across nine observed BGP neighbours.

Notable

• Fifteen answering addresses use one form: a two-letter prefix, the address in dashes, and a three-label domain.
• The two exceptions use a shorter domain instead. One names an ethernet interface on a host; the other is a virtual host, with the third and last octets run together into a single number with no separator.
• Eleven of the twelve blocks share one netname and one allocation date; the twelfth substitutes its own third octet for the date and drops the company from its registrant list.
• The block is held by an individual trading as a partnership, so the registrant is a person rather than a company.
• Eighteen addresses were queried for reverse DNS and seventeen returned a name.

Interesting

• Running the third and last octet together produces a number that reads as one value but is two. It works because the operator knows the convention, and it is unparseable to anyone who does not.
• Two domains in one zone, with infrastructure on the short one and customers on the long one, is a sensible split: it keeps the routers findable by people who need them and everything else generic.
• Twelve routes from one contiguous range, none of them adjacent enough to merge, is the fragmentation that comes from growing a /24 at a time.