BGP Prefix Lookup
Check if an IP prefix is announced in the global BGP routing table. See origin ASN, visibility score, RPKI/ROA status, and AS-PATH details from RIPE RIS collectors worldwide. A free tool by IPv4Center.
What is BGP Visibility?
BGP (Border Gateway Protocol) visibility refers to whether an IP prefix is announced and reachable on the global internet. When a network operator announces a prefix via BGP, route collectors around the world observe this announcement. The visibility score indicates what percentage of these collectors can see the prefix — a higher score means better global reachability. RPKI (Resource Public Key Infrastructure) validation ensures that the AS announcing the prefix is authorized to do so, preventing route hijacking.
How Does This Tool Work?
This tool queries RIPE Stat API, which aggregates data from RIPE RIS (Routing Information Service) route collectors deployed worldwide. It checks the routing status of the prefix, identifies the origin ASN, calculates a visibility score based on how many collectors see the prefix, validates RPKI/ROA status, and provides sample AS-PATHs showing how traffic reaches the prefix from different vantage points.
Frequently Asked Questions
When a prefix is "Announced," it means a network operator is actively advertising that IP range via BGP to the global routing table. Routers worldwide learn about this prefix and can route traffic to it. If a prefix is "Not Announced," it is not visible in the global routing table and traffic cannot be routed to those IPs.
A visibility score above 90% is considered excellent, meaning the prefix is seen by the vast majority of route collectors worldwide. Scores between 70-90% are acceptable but may indicate some filtering. Below 70% could suggest partial announcements, filtering by upstream providers, or recent changes that haven't fully propagated.
RPKI (Resource Public Key Infrastructure) uses ROAs (Route Origin Authorizations) to cryptographically verify that an AS is authorized to announce a specific prefix. A "Valid" status means the ROA matches the announcement. "Invalid" means there is a mismatch (potential hijack). "Not Found" means no ROA exists for this prefix.
An AS-PATH is the sequence of Autonomous Systems (ASNs) that a BGP route traverses from origin to destination. For example, "3333 1234 5678" means the prefix originates from AS5678, passes through AS1234, and reaches AS3333. Shorter AS-PATHs generally indicate more direct routing.
The Announcement History shows which Autonomous Systems (ASNs) have announced this prefix over time, including the date ranges when each ASN was the origin. This is valuable for detecting route hijacks, understanding prefix ownership changes, and verifying that a prefix has been consistently announced by the expected network. If you see unexpected ASNs in the history, it could indicate a past hijack or a legitimate transfer.
A prefix might not be visible for several reasons: it has not been announced by any router, the announcement has been filtered by upstream providers, the prefix size is too small (many networks filter prefixes smaller than /24), or there are RPKI issues causing the route to be rejected. If you recently acquired addresses, check our guides for setup help.
How BGP Routing Works
BGP (Border Gateway Protocol) is the path vector routing protocol that forms the backbone of internet routing, defined in RFC 4271 (BGP-4). Every autonomous system (AS) on the internet uses BGP to exchange reachability information with neighboring networks, enabling over 75,000 autonomous systems to collectively maintain a coherent global routing table containing more than 950,000 IPv4 prefixes.
Unlike interior gateway protocols such as OSPF or IS-IS that operate within a single organization, BGP operates between autonomous systems (eBGP) and within them (iBGP). When a network operator originates a prefix, BGP propagates this route announcement across the entire internet through a series of peer-to-peer TCP sessions on port 179. Each AS that forwards the announcement prepends its own AS number to the AS-PATH attribute, creating a full record of the route's traversal path.
The BGP decision process evaluates multiple path attributes to select the best route when multiple paths exist to the same destination. This deterministic selection algorithm ensures consistent routing decisions across the global internet. BGP supports 4-byte AS numbers as defined in RFC 6793, expanding the ASN space from 65,536 to over 4 billion possible autonomous systems to accommodate internet growth.
BGP Route Selection Process
BGP routers use a deterministic 9-step best path selection algorithm to choose the optimal route when multiple paths to the same prefix exist. Understanding this process is critical for network engineers managing traffic flows and troubleshooting routing issues.
The BGP best path selection criteria, evaluated in strict order, are: (1) Highest weight (Cisco-proprietary, local to router), (2) Highest LOCAL_PREF value (default 100, used for inbound traffic engineering), (3) Locally originated routes preferred (via network statement, aggregate, or redistribution), (4) Shortest AS_PATH length (fewest autonomous systems traversed), (5) Lowest origin type (IGP < EGP < Incomplete), (6) Lowest MED value (Multi-Exit Discriminator, used between adjacent ASes), (7) eBGP preferred over iBGP paths, (8) Lowest IGP metric to the BGP next-hop (nearest exit routing), (9) Oldest eBGP route preferred for stability, followed by lowest router-id as final tiebreaker.
In practice, network operators primarily engineer traffic using LOCAL_PREF for inbound preference, AS_PATH prepending to make paths appear longer, and MED to signal preference between multiple peering points with the same neighbor. Communities (RFC 1997) and large communities (RFC 8092) provide additional signaling mechanisms that allow operators to influence routing decisions in upstream and peer networks without direct configuration access.
BGP in the IPv4 Market
BGP visibility is a critical factor in IPv4 address transfers and the secondary IP market. When an organization purchases IPv4 address space, verifying the BGP routing history and current announcement status of those prefixes is essential due diligence. A prefix with clean routing history, valid RPKI/ROA records, and no bogon or hijack markers commands higher market value and reduces operational risk for the buyer.
After acquiring IPv4 address space through a transfer, the new holder must establish proper BGP announcements from their autonomous system. This involves creating Route Origin Authorization (ROA) objects in the RPKI system to cryptographically bind the prefix to the new origin AS, updating Internet Routing Registry (IRR) objects such as route and aut-num entries, and coordinating with upstream providers to accept the new announcements. The propagation of a new BGP announcement typically reaches full global visibility within 2-5 minutes, though convergence times vary based on network topology and dampening policies.
RPKI validation has become increasingly important in the IPv4 market, with over 40% of IPv4 prefixes now covered by valid ROA records. Major networks including AT&T, NTT, Cloudflare, and Telia implement RPKI-based route origin validation (ROV), meaning prefixes without valid ROAs may experience reduced reachability. For IPv4 buyers, ensuring RPKI readiness of transferred address space is no longer optional — it directly impacts whether the addresses can be routed to all parts of the internet.