What does "TTL expired in transit" mean?

We have a lease line between two sites. When the line is down and I ping to the router on the other site, we normally get the answer "Request timed out," but now we get the answer "TTL expired in transit." What does it mean?

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The "Request timed out" error occurs when the computer you're pinging from doesn't ever get a response back. So, it would be symptomatic of a leased line that is simply down and can't reach the Internet. The "TTL expired in transit" error will only show up if a router that is forwarding the traffic sends an error message back to the computer you're pinging from.

TTL (Time To Live) is a number that is used to track the number of hops or routers a particular packet crosses. If a packet crosses too many routers, an error is returned to the computer that sent the packet. This is to prevent routing loops where a packet is forwarded between two or more routers indefinitely. In short, it means you have a Layer 3 network problem instead of a Layer 1 network problem, and you should call whoever is responsible for your network infrastructure.

This was first published in September 2002

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