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AS21508Comcast Cable Communications, LLC

United StatesRegistryARIN

As of 28th September 2026, AS21508 (Comcast Cable Communications, LLC), a network registered in the United States with ARIN, originates 16 IPv4 prefixes covering 70.1k addresses and 61 IPv6 prefixes. By IPv4 address space that makes it the 3,096th-largest of the 79,544 networks we see originating IPv4, and the 1,006th-largest of 18,428 in the United States. It is seen behind 1 upstream network, most often AS7922 (Comcast Cable Communications, LLC), and in front of 49 downstream networks. 92% of its announcements have a valid RPKI ROA, and none are RPKI-invalid. 100% of its routes reach at least 90% of full-feed peers.

At a glance

IPv4 prefixes

16

IPv6 prefixes

61

IPv4 addresses

70.1k

IPv6 /64s

4M

Upstream graph

The networks AS21508 is seen behind, one and two hops out, drawn from real AS paths.

AS21508Toward the internet core
Upstream graph for AS21508: 3 neighbouring networks observed beyond it across 2 levels. The same networks are listed in the tables below.AS21508Comcast Cable Com…This networkAS7922Comcast Cable Com…AS1299Arelion (fka. Tel…AS2914NTT America, Inc.

Networks observed one and two hops upstream of AS21508 in real AS paths. A thicker line means more vantage points saw that adjacency, so weight tracks how well attested it is — not how much traffic it carries. Adjacency is an observation; whether it is a transit purchase or a settlement-free peering is an inference, and is labelled as one wherever we show it.

Neighbouring networks

101

adjacent networks

Upstreams
11%
Peers
5150%
Downstreams
4949%

Networks carrying this one's traffic toward the rest of the internet.

Upstreams of AS21508
NetworkCountryRelationshipPathsVantage pts
AS7922Comcast Cable Communications, LLCUSPeer8,486147

Prefixes

All 77

The largest blocks AS21508 originates, widest first.

Largest prefixes originated by AS21508
PrefixAddressesVisibility
141.104.0.0/1665.5k81/82
198.90.112.0/221k81/82
50.204.101.0/2425681/82
50.205.217.0/2425682/82
50.216.229.0/2425682/82
50.217.1.0/2425682/82
50.217.207.0/2425682/82
50.218.47.0/2425682/82
50.228.113.0/2425682/82
50.229.113.0/2425682/82

Routing health

How AS21508's own announcements validate against RPKI and how far they propagate. The same measures for the whole routing table are on the routing table in numbers.

RPKI origin validation

  • Valid92.2%71
  • Invalid0.0%0
  • No ROA7.8%6

Propagation

  • Globally propagated90% of full-feed peers or more100.0%77
  • Partially propagated40% to 90%0.0%0
  • Seen by few peersUnder 40%0.0%0

Prefix sizes

IPv4 — 16 prefixes

IPv6 — 61 prefixes

  • /4865.5k × /64100.0%61

Recent changes

Announcements that started or stopped since 29th Aug 2026.

No announcement by AS21508 started or stopped in this period.

Routing data derived from RouteViews MRT archives, BGPKIT relationship inference and public registry data.