Traceroute + ASN Lookup

Traceroute is a network diagnostic tool that maps the path packets take from one computer to another across the internet. It works by sending a series of probes with increasing TTL (Time To Live) values. Each router along the path decrements the TTL; when it hits zero, the router sends back an ICMP “time exceeded” message, revealing its IP address and round-trip time. By incrementing TTL with each probe, traceroute assembles the full path hop by hop.

This tool runs traceroute from the Viewleaf server and enriches each discovered hop with Autonomous System data — the ASN, owning organization, announced IP prefix, and country — so you can see not just the network path but whose infrastructure your traffic is traversing.

An Autonomous System (AS) is a collection of IP address ranges under the control of a single organization that presents a unified routing policy to the internet. Large ISPs, cloud providers, universities, and enterprises each typically operate one or more autonomous systems. An Autonomous System Number (ASN) is the unique identifier assigned to each AS — for example, AS15169 is Google, AS16509 is Amazon Web Services, AS32934 is Meta.

ASNs matter for understanding email deliverability because DMARC aggregate reports include the source IP of every sending server, and the ASN tells you which cloud or hosting provider that IP belongs to. If you see unexpected ASNs in your DMARC reports, it can signal unauthorized use of your domain.

Each row represents one network hop on the path from the Viewleaf server to your target. The columns are:

• # — the sequential hop number, starting at 1.
• IP — the IP address of the router at that hop.
• RTT — round-trip time in milliseconds. Color-coded: green is under 20 ms (fast), amber is 20–79 ms, red is 80 ms or more.
• Country — the country where that IP is registered.
• ASN — the Autonomous System Number. An AWS badge marks Amazon Web Services hops.
• Organization — the network that owns the ASN.
• Prefix — the IP prefix (CIDR block) the hop belongs to.

A subtle horizontal divider between rows marks an AS boundary — where the path crosses from one organization’s network into another’s.

A row showing * * * in the IP column means that router did not respond to the probe within the timeout window. This is normal and happens for several reasons: the router may be configured not to send ICMP time-exceeded messages (common on some enterprise and ISP equipment), the probe may have been filtered by a firewall, or the router may simply be too busy to respond.

A non-responding hop does not mean the path is broken — packets still pass through it; the router just doesn’t identify itself. It’s common to see a few * * * rows even on a fully healthy path, particularly on hops inside large transit networks.

Hops marked Internal have IP addresses within RFC 1918 private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) or other non-routable blocks. These are local network addresses not registered in public ASN databases, so no organization or prefix data is available.

You typically see internal hops at the very beginning of a trace — representing the server’s local gateway or the first few routers inside the hosting provider’s private network — before the path exits to the public internet.

ASN data is looked up via the Team Cymru IP-to-ASN mapping service. If a hop IP is not in their database, ASN and organization fields will be blank. This happens for private IPs (see above), newly allocated addresses not yet indexed, or very small networks with minimal internet presence. In practice the vast majority of public internet hops will have ASN data; gaps are most common at the beginning of the path or for hops inside carrier networks using unregistered internal addresses.