Please Whitelist This Site?
I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)
If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.
If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK.
Thanks for your understanding!
Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide
|
NOTE: Using software to mass-download the site degrades the server and is prohibited. If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.
|
|
|
|
ICMPv4 Time Exceeded Messages
(Page 3 of 3)
Applications of Time Exceeded Messages
As an ICMP error message type, ICMP
Time Exceeded messages are usually sent in response to the two
conditions described above (TTL or reassembly timer expiration).
Generally, Time To Live expiration messages are generated by
routers as they try to route a datagram, while reassembly violations
are indicated by end hosts. However, there is actually a very clever
application of these messages that has nothing to do with reporting
errors at all.
Key Concept: ICMPv4 Time Exceeded messages are sent in two different time-related circumstances. The first is if a datagrams Time To Live (TTL) field is reduced to zero, causing it to expire and the datagram to be dropped. The second is when all the pieces of a fragmented message are not received before the expiration of the recipients reassembly timer. |
The TCP/IP traceroute (or
tracert) utility is used to show the sequence of devices over
which a datagram is passed on a particular route between a source and
destination, as well as the amount of time it takes for a datagram to
reach each hop in that route. This utility was originally implemented
using Time Exceeded messages by sending datagrams with successively
higher TTL values. First, a dummy datagram is sent
with a TTL value of 1, causing the first hop in the route to
discard the datagram and send back an ICMP Time Exceeded; the
time elapsed for this could be measured. Then, a second datagram is
sent with a TTL value of 2, causing the second device in the
route to report back a Time Exceeded, and so on. By continuing
to increase the TTL value we can get reports back from each hop
in the route. See
the topic describing traceroute for more details on its operation.
If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support! |
|
|
Home -
Table Of Contents - Contact Us
The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.
|