asn.dev

Observed topology

AS21508 COMCAST-21508 - Comcast Cable Communications, LLC

Unclassified DROP-listed space ARIN Cable/DSL/ISP

Upstreams 1 carry this network
Downstreams 48 this network carries
Adjacent (IPv4) 49
Adjacent (IPv6) 7
Upstream graph Who carries AS21508, and who carries them, drawn as a map up to the transit-free core. 0 exchanges Where AS21508 physically turns up to peer, and its address on each fabric.

Transit

Upstream networks

inferred

Networks observed carrying traffic for AS21508: the AS immediately before it in a routing path. Ranked by how many paths showed the relationship, which reflects how widely it is used, not how much traffic crosses it.

ASNetworkTypeFamiliesPaths seen
AS7922Comcast Cable Communications, LLCResidentialIPv4 IPv62,911

Transit

Downstream networks

All 48

Networks for which AS21508 was observed as the last hop before the origin, meaning it appears to provide them transit.

ASNetworkTypeFamiliesPaths seen
AS40641MGW Telephone Company, Inc.UnclassifiedIPv4 IPv6414
AS15297EPLUS, Inc.UnclassifiedIPv4180
AS401426St. Mary's Medical Center, Inc.UnclassifiedIPv4 IPv6122
AS18773County of HenricoUnclassifiedIPv4120
AS396083Framatome Inc.UnclassifiedIPv4120
AS400114Apogee Telecom Inc.UnclassifiedIPv4120
AS15173Newmarket CorporationUnclassifiedIPv4116
AS2134Santander Global Technology and Operations, S.L.UnclassifiedIPv4108
AS13335Cloudflare, Inc.HostingIPv4 IPv691
AS54113Fastly, Inc.HostingIPv4 IPv691

All 48 downstreams →

Adjacency

Adjacent networks

All 50

Every AS seen directly next to AS21508 in a routing path, in either direction.

ASNetworkTypeFamiliesPaths seen
AS7922Comcast Cable Communications, LLCResidentialIPv4 IPv65,443
AS40641MGW Telephone Company, Inc.UnclassifiedIPv4 IPv6414
AS15297EPLUS, Inc.UnclassifiedIPv4180
AS401426St. Mary's Medical Center, Inc.UnclassifiedIPv4 IPv6122
AS18773County of HenricoUnclassifiedIPv4120
AS396083Framatome Inc.UnclassifiedIPv4120
AS400114Apogee Telecom Inc.UnclassifiedIPv4120
AS15173Newmarket CorporationUnclassifiedIPv4116
AS2134Santander Global Technology and Operations, S.L.UnclassifiedIPv4108
AS13335Cloudflare, Inc.HostingIPv4 IPv691

All 50 adjacent →

Provenance

Where this comes from

Derived from routing tables collected at 2026-11-13 10:00 UTC by route-views2,rrc00, as seen from 75 BGP vantage points across 74.40M route entries. These are observations from those vantage points, not a complete or authoritative view of the internet.

Inferred from path position, not from any declaration by either party. A network appearing here is carrying these routes; whether that is a paid transit arrangement, a backup, or something else is not something routing data can tell you. Adjacency is not the same as peering. Being next to each other in a path covers paid transit, settlement-free peering and customer connections alike, and routing data cannot distinguish them. Treat this as "these networks exchange routes", nothing more specific.

Cross-check against RIPEstat or BGP.tools, which observe from a different and larger set of vantage points.