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What is Traceroute?
Traceroute is a network diagnostic tool that traces the path that packets take from your computer to a destination server on the internet. When you send data across the internet, it doesn't travel directly from point A to point B. Instead, it hops through multiple routers and gateways, each forwarding your data closer to its final destination. Traceroute reveals this entire journey, showing you every intermediate step along the way.
The tool works by sending packets with incrementally increasing TTL (Time To Live) values. Each router that receives a packet decreases its TTL by 1. When TTL reaches 0, the router sends back an ICMP "Time Exceeded" message, revealing its location in the path. By measuring the time it takes for these responses to return, traceroute calculates the round-trip time (latency) to each hop. This information is invaluable for diagnosing network problems, identifying routing issues, and understanding internet infrastructure.
Understanding Traceroute Results
Hops
Each hop represents a router or gateway that forwards your packets. The hop number shows its position in the path, with hop 1 being closest to you and higher numbers farther away.
Latency / RTT
Round-trip time measured in milliseconds (ms) shows how long it takes for packets to reach that hop and return. Lower values indicate faster connections, while sudden spikes can reveal bottlenecks.
Packet Loss
When routers fail to respond or drop packets, you'll see missing data or timeouts. This can indicate network congestion, firewall rules, or connectivity problems at specific hops.
Asterisks (*)
Asterisks appear when routers don't respond to traceroute probes. This doesn't always mean there's a problem - many routers are configured to not respond to traceroute for security reasons.
Why Use Traceroute?
Diagnose Slow Connections
Identify which hop in the network path is causing high latency. If one router shows significantly higher response times than others, it may be a bottleneck affecting your connection speed.
Find Network Bottlenecks
Discover where packets are being delayed or dropped. Sudden increases in latency at specific hops reveal congestion points, helping you understand where network performance degrades.
Identify Routing Issues
See if your traffic is taking an inefficient path to its destination. Sometimes packets route through unexpected countries or networks, indicating suboptimal routing configurations.
Verify ISP Routing
Confirm that your Internet Service Provider is routing traffic efficiently. Check if your packets are staying on your ISP's network or being handed off to other providers appropriately.
Troubleshoot Timeouts
When you can't reach a website or service, traceroute shows exactly where the connection fails. This helps determine if the problem is with your network, your ISP, or the destination server.
Network Planning
Understand the infrastructure between your location and important servers. Use this information for capacity planning, selecting server locations, or choosing network providers.
Frequently Asked Questions
What do the asterisks (*) in traceroute mean?
Asterisks (*) appear when a router along the path doesn't respond to traceroute probes within the timeout period. This can happen for several reasons:
- Firewall configuration: Many routers are configured to silently drop ICMP packets (used by traceroute) for security reasons.
- Rate limiting: Routers may limit responses to diagnostic tools to prevent being overwhelmed by probe traffic.
- Router policy: Network administrators often disable ICMP responses on production routers to reduce unnecessary traffic.
- Packet loss: Temporary network congestion or issues may cause packets to be dropped.
Seeing asterisks doesn't necessarily indicate a problem. If subsequent hops respond normally and you can reach the final destination, the network path is functioning correctly despite the non-responsive routers.
Why does traceroute show high latency at one hop?
High latency at a single hop can occur for several reasons:
- Geographic distance: Hops that cross continents or oceans naturally have higher latency due to the physical distance signals must travel.
- Router congestion: A busy router processing high traffic volumes may take longer to respond to traceroute probes.
- Low priority processing: Routers prioritize actual data traffic over diagnostic probes, so ICMP responses may be delayed.
- Network peering points: Where one network hands off traffic to another, there may be additional processing time.
What matters most is the latency at the final destination and whether it's acceptable for your needs. A single slow hop in the middle doesn't necessarily mean your overall connection is slow - look at the end-to-end latency instead.
What's the difference between traceroute and ping?
Ping tests the reachability and latency to a single destination. It sends packets directly to the target and measures round-trip time, telling you if the host is reachable and how fast the connection is.
Traceroute reveals the entire path packets take to reach the destination. It shows every router along the way and the latency to each hop, helping you understand the route and identify where problems occur.
Key differences:
- Ping gives you end-to-end latency; traceroute shows latency at each step
- Ping tells you if a host is reachable; traceroute shows where the connection fails
- Ping is faster and simpler; traceroute provides more detailed diagnostic information
- Use ping for quick connectivity checks; use traceroute for troubleshooting network issues
How many hops is normal?
The number of hops varies depending on the distance and routing between you and the destination. Typical hop counts include:
- Local network (same city): 5-10 hops
- Regional (same country): 10-15 hops
- International: 15-25 hops
- Very distant locations: 20-30 hops
Well-connected websites using CDNs (Content Delivery Networks) like Cloudflare or AWS CloudFront often show fewer hops (5-8) because they have servers geographically close to most users. The maximum TTL is typically set to 30 hops, meaning traceroute will stop after 30 routers even if the destination hasn't been reached.
More hops don't necessarily mean worse performance - what matters is the total latency and whether packets are being lost along the way.
Why does my traceroute stop partway?
If traceroute stops before reaching the destination, several issues might be occurring:
- Firewall blocking: The destination server's firewall may be blocking ICMP packets entirely, preventing traceroute from completing.
- Network outage: A router or connection further down the path may be down or experiencing problems.
- Routing loop: Packets may be stuck in a circular routing path, eventually exceeding the maximum hop count.
- Maximum hops reached: If the destination is more than 30 hops away (the typical maximum), traceroute will stop.
- Packet filtering: Some networks aggressively filter ICMP traffic, causing traceroute to fail even though normal traffic gets through.
If traceroute doesn't complete but you can still access the destination in your browser, the server is reachable but blocking traceroute packets specifically. This is common with security-conscious servers.