When a website is slow or unreachable for users in a specific country or ISP network, standard ping tests can confirm high latency or packet loss, but they cannot tell you where along the journey the packet got stuck.

Traceroute solves this by uncovering every intermediate router (or "hop") between the source client and destination server, revealing the exact path your packets travel across the global internet.

This guide explains how traceroute operates, how to interpret each column of output, what asterisks (* * *) really mean, and how to use an online traceroute test to isolate network bottlenecks.

How traceroute works: Exploiting IP Time-to-Live (TTL)

Every IP packet contains a header field called Time to Live (TTL). The TTL is an integer (typically starting at 64 or 128) designed to prevent lost packets from circulating forever in routing loops.

Every time a router forwards a packet, it decrements the TTL by 1. When the TTL reaches 0, the router discards the packet and sends back an ICMP message: Type 11 - Time Exceeded in Transit.

Traceroute leverages this mechanism intentionally:

1. It sends a probe packet with TTL = 1. The first router decrements TTL to 0, drops the packet, and responds with ICMP Time Exceeded. Traceroute records Hop 1 and its round-trip time (RTT).
2. It sends another packet with TTL = 2. Hop 1 forwards it; Hop 2 decrements TTL to 0 and responds. Traceroute records Hop 2.
3. This increments sequentially (TTL = 3, 4, 5...) until the packet reaches the destination server, which responds with a standard ICMP Echo Reply or TCP/UDP port unreachable response.

Reading a traceroute output line by line

A typical traceroute output looks like this:

Hop  Hostname / IP Address                    RTT 1    RTT 2    RTT 3
1    router.local (192.168.1.1)               0.8 ms   0.7 ms   0.9 ms
2    100.64.0.1 (Carrier CGNAT Gateway)      4.2 ms   4.1 ms   4.3 ms
3    isp-core-node.net (203.0.113.1)          8.5 ms   8.2 ms   8.4 ms
4    as13335.cloudflare.ix.net (198.51.100.5) 12.1 ms  11.8 ms  12.0 ms
5    172.67.182.25 (Destination Server)       12.4 ms  12.2 ms  12.5 ms

• Hop Number: The sequential router index along the network transit path.
• Hostname / IP: The reverse DNS hostname (if available) and IP address of the router at that hop.
• Round-Trip Times (RTT 1, 2, 3): Traceroute sends multiple probes (usually 3) per hop. The times show how many milliseconds it took to send the probe and receive the ICMP reply.

What do asterisks (* * *) mean?

Seeing asterisks (* * *) on a traceroute is one of the most misunderstood results in networking.

Hop  Hostname / IP Address         RTT 1    RTT 2    RTT 3
6    * * *                         Request timed out
7    edge01.datacenter.com         45.2 ms  44.9 ms  45.1 ms

Asterisks on intermediate hops (Harmless)

Many modern core routers prioritize forwarding production transit traffic and de-prioritize or completely disable ICMP Time Exceeded generation. If Hop 6 shows * * * but Hop 7 and subsequent hops respond with normal low latencies, there is no packet loss or outage. The router is simply configured to ignore traceroute probes.

Asterisks continuing to the destination (Outage or Firewall)

If asterisks begin at a certain hop and continue until the end of the trace:

Hop  Hostname / IP Address         RTT 1    RTT 2    RTT 3
8    border-gw.hosting.net         38.2 ms  38.0 ms  38.4 ms
9    * * *                         Request timed out
10   * * *                         Request timed out

This indicates either:

• The destination server or its fronting firewall is configured to block ICMP/UDP packets.
• An upstream routing failure or network partition is preventing packets from reaching the server beyond Hop 8.

Identifying real routing issues

1. Sudden latency spikes that persist

If latency jumps dramatically at a specific hop and remains high for all subsequent hops:

Hop  Hostname / IP Address                    Avg RTT
3    isp-gateway-nyc.net (198.51.100.1)       14 ms
4    transatlantic-cable-lon.net (203.0.113.8) 98 ms  <-- Intercontinental fiber jump
5    dc-london-core.net (192.0.2.14)          101 ms

A jump from 14ms to 98ms between New York and London is physically expected due to the speed of light in undersea fiber cables. However, if latency jumps from 15ms to 250ms between two routers in the same city, it signals severe congestion on that specific peering link.

2. Routing loops

A routing loop occurs when misconfigured BGP or OSPF tables cause two routers to bounce packets back and forth until the TTL expires:

Hop 12   router-a.transit.net (198.51.100.10)   45 ms
Hop 13   router-b.transit.net (198.51.100.11)   46 ms
Hop 14   router-a.transit.net (198.51.100.10)   47 ms
Hop 15   router-b.transit.net (198.51.100.11)   48 ms

Routing loops cause 100% packet loss for affected destinations and require intervention by network engineers at the responsible transit provider.

How to test your network path with PingXD

1. Open the PingXD Traceroute Tool.
2. Enter your destination domain name or IP address.
3. Select your testing origin (e.g., North America, Europe, or Asia-Pacific).
4. Review the interactive hop diagram to inspect latency progression, AS numbers, and intermediate carrier nodes.

Complement your traceroute results with a Ping latency test and a DNS lookup verification to obtain a complete, 360-degree diagnostic view of your network connectivity.