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Mr.X
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what is ttl and why there is difference when pinging different devices in same lan

just a general question
when I try to ping my router from a local computer which is connected with lan cable- ping time is ms<1, ttl is 255
when I ping my server in same lan:
ping time is <1, but ttl is 128

why there is vary in ttl when I ping my sever and router from same local computer . anything I need to worry ??
Windows NetworkingWindows Server 2008TCP/IP

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Seth Simmons

8/22/2022 - Mon
ASKER CERTIFIED SOLUTION
Kimputer

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Mr.X

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ok thank.
and do you know any software which I use to find bandwidth problems or which computer/devices consumes more bandwidth ?
SOLUTION
noci

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hypercube

I would recommend Paessler PRTG.  Depending on the number of devices, there is a free version that works quite well for this purpose.  
You may have to learn a little about how to get devices to communicate with the monitor but they make it as easy as possible.
Kimputer

One of the cheapest way to find out more about bandwidth usage, is to have a very old network hub (but that limits you to 100mbits), or a newer smaller smart switch with port mirror support.
With a laptop on one port, and the most outer edge outgoing network cable on the other port, you can capture the full scope of the outgoing network, and see which device is using the most bandwith (With the laptop running Wireshark, and having the network statistics window open).

Most enterprise level hardware will also do with their built-in software, but it costs quite a lot more.
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noci

Even less expensive hardware can do this.  Zywall USG
hypercube

"TTL" is a count-down number in the packets your ping sends out.  Each hop reduces it by one when it forwards.  It's used to stop packets from running around the internet forever.  If it's zero or some other lower threshold number, the routers drop the traffic.  It could vary if the paths vary.
noci

@fred: TTL has a definition of time (in seconds) so 63 means 63 seconds maximum lifetime.
A router is required to subtract their processing time from it, where the processing time is AT least 1 even if it is actually faster.
So a router may subtract a bigger number than 1.

See: https://tools.ietf.org/html/rfc791page 13
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hypercube

noci:  Thank you for pointing that out and giving me an opportunity to learn something!  I didn't know this before.
It appears that in fact, TTL is the *upper bound* in seconds for how long the packet may live.
That's because while a router may process the packet in less than a second, it has to subtract 1 second.
If one assumes that a router will process a packet MUCH faster than that, then the number subtracted is assumed to always be "1" and the units of "seconds" becomes pretty meaningless.
Under that assumption, my simplification turns out to be correct.
But I admit that I don't know the statistics. i.e. "What is the distribution of processing times for packets traversing routers?"  But, the impression I get is that a typical time is measured in microseconds.
noci

Correct, now it is, in the early days of internet that was not the case.  (1974... ish)
On a 30 Baud (30 bps)  telex line, the minimal packet takes 2 - 3 seconds to transmit...  and that time should be taken into account.
Seth Simmons

No comment has been added to this question in more than 21 days, so it is now classified as abandoned.

I have recommended this question be closed as follows:

Split:
-- 'Kimputer' (https:#a42984646)
-- 'noci' (https:#a42984655)


If you feel this question should be closed differently, post an objection and the moderators will review all objections and close it as they feel fit. If no one objects, this question will be closed automatically the way described above.

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