Verified: 2026-10-17By Alex Chen (Lead BGP Architect)BGP & PeeringDB9 Min Read

How to Lookup ASN Announced Prefixes and Upstream Peering

An operational methodology for auditing Autonomous Systems, discovering announced CIDR prefixes, mapping upstream transit dependencies, and inspecting public IXP interconnections.

Quick Answer

Auditing an ASN requires querying three primary intelligence sources: Internet Routing Registries (IRR) to extract registered route and route6 objects, global BGP route collectors (RouteViews, RIPEstat) to discover actively announced prefixes and upstream transit carriers, and PeeringDB to examine physical Internet Exchange Point (IXP) peering presence.

IRR Database Queries: whois queries against RADB reveal all authorized route announcements.
Upstream Dependency Audit: Looking glasses uncover single points of failure across Tier-1 transit paths.
PeeringDB Interconnections: Identifies zero-settlement peering at major colocation facilities.

1. The Anatomy of an ASN Footprint

Every Autonomous System operates an interconnected matrix of transit agreements, peering sessions, and announced IP prefixes:

1. Originated Prefixes:IPv4 (/24 or larger) and IPv6 (/48 or larger) blocks announced via BGP.

2. Upstream Transit Providers:Paid Tier-1 / Tier-2 carriers (e.g. Lumen, Telia/Arelion, NTT, Cogent).

3. Settlement-Free Peers:Direct fiber interconnects at IXPs exchanging traffic bilaterally at zero cost.

4. Downstream Customers:Smaller networks and enterprise clients purchasing transit from this ASN.

2. Comparison of ASN Intelligence Tools

Compare the primary platforms utilized by network architects to analyze ASN topologies:

Comparative Analysis of ASN Routing Intelligence Tools
Platform	Primary Intelligence Provided	Update Speed	Access Method	Best Used For
Hurricane Electric (bgp.he.net)	Prefix counts, peer graphs, IXP presence, DNS servers	Daily BGP snapshot	Web GUI	Fast visual inspection of peers and upstreams
RIPEstat ASN API	Live routing status, historical prefix changes, WHOIS objects	Real-time / Historical	REST API & Web UI	Programmatic CI/CD and automation scripts
PeeringDB	Colocation facilities, public peering exchanges, peering contact	Live (Operator updated)	REST API & Web UI	Verifying datacenter presence and peering policy
RADB / IRR Registries	Registered route/route6 objects, as-set membership	Immediate upon commit	Port 43 WHOIS	Validating authorized BGP route announcements
BGPView API	Clean aggregated REST endpoints for ASN upstreams/downstreams	Hourly	Free REST API	Quick developer application integrations

ASN Routing Architecture Audit Decision Tree


                 [ Investigate ASN Routing Architecture ]
                                    |
           +------------------------+------------------------+
           |                        |                        |
     [ Announced Prefixes ]    [ Transit & Peering ]    [ Physical Presence ]
     What subnets does it own? Who provides upstream?   Where does it peer?
           |                        |                        |
     Query IRR Database        BGP Looking Glass        PeeringDB Profile
     whois.radb.net            bgp.he.net / RIPEstat    Exchange Points (IXPs)
     route / route6 objects    Upstream Tier-1 Carries  Colocation Facilities
           |                        |                        |
           +------------------------+------------------------+
                                    |
                        [ Complete Network Footprint ]
                   Multi-homed diversity & redundancy rating

3. How to Query IRR for All Announced Prefixes via Terminal

The Merit Routing Assets Database (RADB) allows direct recursive querying of all routes originated by an ASN using the !g command:

Query All IPv4 Prefixes Originated by ASN:whois -h whois.radb.net "!gas13335"

Query All IPv6 Prefixes (6as command):whois -h whois.radb.net "!6as13335"

4. Practical Diagnostics: Querying Upstream Carriers with PeeringDB API

Automate the discovery of an ASN's public peering points and traffic volume:

Fetch PeeringDB ASN Summary:curl -s "https://www.peeringdb.com/api/net?asn=13335" | jq '.data[0] | {name: .name, traffic: .info_traffic, policy: .policy_general}'

Fetch BGP Routing Status via RIPEstat:curl -s "https://stat.ripe.net/data/routing-status/data.json?resource=AS13335" | jq '.data'

Frequently Asked Questions

How do I find every IP prefix announced by an Autonomous System?

You can query Internet Routing Registries (IRR) like RADB using whois (e.g. whois -h whois.radb.net "!gAS13335") to list all registered route objects, or inspect live BGP table dumps from global route collectors like RIPEstat or Hurricane Electric BGP Toolkit (bgp.he.net).

What is the difference between an upstream transit provider and a peering partner?

An upstream transit provider is a paid carrier that delivers the entire global Internet routing table (over 950,000 IPv4 routes) to the customer ASN. A peering partner is a network with which the ASN directly exchanges traffic—often for free at an Internet Exchange Point (IXP)—strictly for their mutual customers, without providing transit to the rest of the Internet.

What is PeeringDB and why is it essential for network engineers?

PeeringDB (peeringdb.com) is a globally recognized community database where network operators publish their physical interconnection points, presence at colocation datacenters, public peering exchange memberships (IXPs), and peering policies (Open, Selective, or Restrictive).

What is an IRR "as-set" object?

An as-set (or AS macro) is an RPSL routing object that groups an ASN and all of its downstream customer ASNs into a single identifier (e.g. AS-CLOUDFLARE). Upstream transit providers use as-sets to build automated BGP prefix filters that prevent unauthorized routes from being announced.

Data & Technical Sources

IETF RFC 4271 — A Border Gateway Protocol 4 (BGP-4 Specification)
IETF RFC 2622 — Routing Policy Specification Language (RPSL / IRR)
PeeringDB API Documentation — Public REST API schema for peering and interconnection data