When pinging another computer on your network, what does the TTL mean? Is that a measure of time? What is an acceptable TTL if that is time? We have an Ethernet with about 10 computers in one office.
This is the Time To Live. Each time a packet goes through a router, this number is decreased by one. When it reaches zero the packet is dropped. This basically makes sure that if the packet gets lost it doesn’t hang around the network forever.
In most packets the TTL is set to 60, but it’s set to 255 for ping. From the TTL you can get an indication of how many routers the packet has passed through. Also, if different packets have different TTLs, it means that the packet is taking different routes through the network. This may be a bad thing, and can indicate a faulty configuration.
If you need more info, searching on the web for ‘ping’ (and possibly ‘traceroute’) should give more details.
Heh - the old CCIE Drake test had the question: “What is the purpose of the TTL field ?” and one of the answers were “To make us ponder the brevity of life”…
dylan nailed it. I belive it was introduced specifically to prevent routing loops, which are (rightly) considered a Bad Thing.
S. Norman
A side note: The guy who wrote the original ping program died within the last couple of weeks. I looked for a link but couldn’t find one.
Guess the poor guy should have set his TTL a little higher…
which I got from here:
Let’s all ponder the irony of this for a moment