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What is TTL and how is it used?
| Posted by OConner, 08-24-2012, 12:54 PM |
| Hello,
When pinging a website or an IP using the CMD I always ask "What is that TTL?".
Well, that is it? I know it stands for Time To Live, but how is it used and should TTL be a high or low number?
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| Posted by XSV, 08-24-2012, 01:28 PM |
| You can read up on it here, http://en.wikipedia.org/wiki/Time_to_live.
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| Posted by BestServerSupport, 08-25-2012, 01:27 AM |
| TTL means Time To Leave. The amount of time (in miliseconds) a packet should wait before reaching to destination. The ideal range for TTL is 50-300 milliseconds.
For example. if there is 50-300 milliseconds range set in TTL then after this value, you will receive request timeout error in ping command.
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| Posted by Collabora, 08-25-2012, 01:40 AM |
| That is incorrect
TTL or Time to Live refers to how many routers your packet can go through before it expires. Usually a packet finds its home in less than 32 hops, but 64-128 is a good default. I believe 128 hops is the default for windows
Every time a packet passes through a router the TTL number is one less than before. If this counter didn't exist the internet as we know it could be at 100% bandwidth bouncing these packets back and forth that would never find a home if the destination is unreachable. That would make the internet unusable.
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| Posted by dotHostel, 08-25-2012, 08:50 AM |
| From Wikipedia:
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| Posted by Collabora, 08-25-2012, 10:00 AM |
| With icmp packets ttl is a counter not a timestamp.
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| Posted by dotHostel, 08-25-2012, 10:42 AM |
| http://www.ietf.org/rfc/rfc792.txt
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| Posted by dotHostel, 08-25-2012, 11:00 AM |
| RFC 1812, page 85:
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| Posted by Collabora, 08-25-2012, 11:13 AM |
| You're quote in red is exactly what I am saying. You can use a clock as a counter, for example if I am drinking a sixpack I can start the clock at 6:00 and decrement the clock 1 hour for each beer I drink to 0:00 -- even if I down each beer in 10 seconds. But it has nothing to do with the actual time. The clock is behaving as a counter, not a timekeeper.
If the starting TTL number did not decrease by 1 with every hop (regardless of time itself) the internet would soon be 100% filled with icmp packets looking for a destination
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| Posted by loodwood, 08-25-2012, 11:20 AM |
| TTL s Time To Live in Seconds
is time to me as well..
the time a packet listens
when you do for testing purpose like ICMP we are testing the router in that case only
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| Posted by dotHostel, 08-25-2012, 11:28 AM |
| Clearly the 2 relevant RFCs say TTL is not a counter.
RFC 792: Time to live in seconds
RFC 1812: timer limiting the lifetime of a datagram
Wikipedia is very precise:
In theory, under IPv4, time to live is measured in seconds, although every host that passes the datagram must reduce the TTL by at least one unit.
In practice, the TTL field is reduced by one on every hop.
To reflect this practice, the field is renamed hop limit in IPv6
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| Posted by dotHostel, 08-25-2012, 11:47 AM |
| According to the RFCs the clock could be decremented 2+ hours for each beer
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