Network · AS18731

AS18731 Cityside Fiber

AS18731 (Cityside Fiber) looks like an internet service provider, so its addresses are mostly real home, business or mobile connections.

Network check ASN

AS18731

OwnerCityside Fiber
KindInternet service provider
Servers, not peopleno
IPv4 addresses4,864
IPv4 ranges4
IPv6 ranges1

Risk score0

Nothing suspicious found.

Largest IPv4 ranges

157.238.80.0/20
23.164.40.0/24
154.50.58.0/24
128.177.138.0/24

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

Check an IP address →

Detect it in code

Spot AS18731 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 AS18731

Is AS18731 a datacenter or VPN network?

AS18731 (Cityside Fiber) looks like an internet service provider, so its addresses are mostly real home, business or mobile connections.

Who owns AS18731?

AS18731 is registered to Cityside Fiber. It announces about 4,864 IPv4 addresses.

How do I detect traffic from AS18731?

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.