Network · AS21821

AS21821 Montefiore Medical Center

AS21821 (Montefiore Medical Center) looks like an internet service provider, so its addresses are mostly real home, business or mobile connections.

Network check ASN

AS21821

OwnerMontefiore Medical Center
KindInternet service provider
Servers, not peopleno
IPv4 addresses1,024
IPv4 ranges3
IPv6 ranges0

Risk score0

Nothing suspicious found.

Largest IPv4 ranges

216.255.100.0/23
144.121.104.0/24
144.121.102.0/24

Ranges and owner from DB-IP (CC BY 4.0), updated 2026-10-22.

Check an IP address →

Detect it in code

Spot AS21821 traffic at signup.

Send the visitor's IP. The response includes the ASN, the owner and flags.hosting.

curl https://veqen-app.com/v1/ip/check \
  -H "Authorization: Bearer $VEQEN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"ip": "203.0.113.7"}'

import os, requests

r = requests.post(
    "https://veqen-app.com/v1/ip/check",
    headers={"Authorization": f"Bearer {os.environ['VEQEN_API_KEY']}"},
    json={"ip": "203.0.113.7"},
    timeout=10,
)
result = r.json()
print(result["risk"]["verdict"], result["risk"]["reasons"])

const res = await fetch("https://veqen-app.com/v1/ip/check", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${process.env.VEQEN_API_KEY}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({"ip": "203.0.113.7"}),
});
const result = await res.json();
console.log(result.risk.verdict, result.risk.reasons);

Questions

About AS21821

Is AS21821 a datacenter or VPN network?

AS21821 (Montefiore Medical Center) looks like an internet service provider, so its addresses are mostly real home, business or mobile connections.

Who owns AS21821?

AS21821 is registered to Montefiore Medical Center. It announces about 1,024 IPv4 addresses.

How do I detect traffic from AS21821?

Call the Veqen IP check with the visitor's address. The response includes the ASN, the owner and whether the network is a datacenter, VPN network, relay or ISP.