AS10753 LUMEN-LEGACY-L3-CUSTOMER-SHARED-USE

LUMEN-LEGACY-L3-CUSTOMER-SHARED-USE is registered to Level 3 Parent, LLC (now part of Lumen), and the handle says exactly what it is: a shared-use AS number in the sense of RFC 2270. It does not represent one network. It is a single AS number that Lumen lends to many separate, unrelated customers who buy transit only from Lumen and need their space originated somewhere.

What it's used for

Because it is shared, this ASN is one of the rare cases where the routing table actively misleads. RIS observes 733 announced IPv4 prefixes carrying 593,664 addresses, 17 IPv6 prefixes, and 61 observed neighbours — numbers that would suggest a large carrier if you read them as one organisation. They are not one organisation. They are hundreds of independent end customers, each single-homed to Lumen, whose prefixes all happen to be originated from the same borrowed number.

The practical consequences matter for anyone consuming this data:

• It cannot be geolocated as a unit. Its prefixes land wherever the individual customers are.
• It cannot be classified as a unit. One /24 in here may be a hospital, the next a county government, the next a small hosting shop.
• Its size means nothing about Lumen. These are customer routes, not Lumen backbone.

The announced space bears this out — it is a jumble of unrelated legacy blocks (164.156.0.0/16, 138.15.0.0/16, 147.207.0.0/17, 199.20.128.0/17 and hundreds more) with no common structure, exactly what you would expect from an aggregation of separate assignments.

Notable

RFC 2270, published in 1998, exists precisely so that a provider does not have to burn a globally unique AS number on every single-homed customer. AS numbers used this way are the main reason "which AS is this IP in?" is sometimes an unanswerable question about who actually operates a network.