AS9378 CABLENET JCOM Co., Ltd.

AS9378 (CABLENET) is registered to JCOM Co., Ltd. — J:COM, Japan's largest cable operator. The CABLENET handle and the cablenet.ne.jp domain come from a regional Saitama cable company that was folded into the J:COM group through the long consolidation of Japan's CATV industry, and the ASN continues to carry that operation's subscribers.

What it's used for

Pure cable-modem eyeball access. RIS sees 36 IPv4 prefixes but only 45,056 addresses, no IPv6, and exactly one observed BGP neighbour — a stub hanging off a single upstream, almost certainly another J:COM ASN acting as the group backbone. Reverse DNS is uniform and unambiguous: every sampled address resolves to cNNNNNN.netAABBB.cablenet.ne.jp, a mechanical per-customer naming scheme keyed off the address itself. That pattern, spread across many small /20 and /21 blocks from unrelated parent ranges (61.215, 219.124, 180.131, 124.195, 218.45, 202.179, 110.93, 27.113, 103.3), is the fingerprint of a cable operator that grew by acquiring franchises and inherited their address scraps.

Notable

• The high prefix-to-address ratio (36 prefixes for ~45k addresses) is deaggregation, not scale. Many announcements are a /20 alongside the /21s inside it.
• Do not confuse this ASN with J:COM's main network [AS9824](https://asn.ipinfo.app/AS9824). Both belong to the same company, but this one is the regional cable-access remnant; the group's larger footprint and peering live elsewhere.
• A single BGP neighbour means there is no redundancy visible at the AS level. This network's reachability depends entirely on its parent.