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.

The Book is Here... and Now On Sale!

Searchable, convenient, complete TCP/IP information.
The TCP/IP Guide

Custom Search







Table Of Contents  The TCP/IP Guide
 9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)
      9  TCP/IP Internet Layer (OSI Network Layer) Protocols
           9  Internet Control Message Protocol (ICMP/ICMPv4 and ICMPv6)
                9  ICMP Message Types and Formats
                     9  ICMP Version 6 (ICMPv6) Error Message Types and Formats

Previous Topic/Section
ICMPv6 Packet Too Big Messages
Previous Page
Pages in Current Topic/Section
1
2
Next Page
ICMPv6 Parameter Problem Messages
Next Topic/Section

ICMPv6 Time Exceeded Messages
(Page 2 of 2)

ICMPv6 Time Exceeded Message Format

The format for ICMPv6 Time Exceeded messages can be found in Table 105 and Figure 155.


Table 105: ICMPv6 Time Exceeded Message Format

Field Name

Size (bytes)

Description

Type

1

Type: Identifies the ICMPv6 message type; for Time Exceeded messages this is set to 3.

Code

1

Code: Identifies the “subtype” of time error being communicated. A value of 0 indicates expiration of the Hop Limit field; a value of 1 indicates that the fragment reassembly time has been exceeded.

Checksum

2

Checksum: 16-bit checksum field for the ICMP header, as described in the topic on the ICMP common message format.

Unused

4

Unused: 4 bytes left blank and not used.

Original Datagram Portion

Variable

Original Datagram Portion: As much of the IPv6 datagram as will fit without causing the size of the ICMPv6 error message (including its own IP header) to exceed the minimum IPv6 maximum transmission unit (MTU) of 1280 bytes.



Figure 155: ICMPv6 Time Exceeded Message Format

 


Key Concept: Like their ICMPv4 namesakes, ICMPv6 Time Exceeded messages are sent in two different “time-related” circumstances. The first is if a datagram’s Hop Limit 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 recipient’s reassembly timer expires.


Applications of Time Exceeded Messages

In IPv4, ICMP Time Exceeded messages are used both as an error message and in a clever application to implement the TCP/IP traceroute command. This is done by first sending a “dummy” datagram is sent with a Time To Live value of 1, causing the first hop in the route to discard the datagram and send back an ICMP Time Exceeded. Then, a second datagram is sent to the same destination with a TTL value of 2, causing the second device in the route to report back a Time Exceeded, and so on.

There is of course an IPv6 version of traceroute, sometimes called traceroute6. Due to IPv6 and its protocols and applications still being in development, I have not been able to confirm definitively that traceroute6 is implemented using ICMPv6 Time Exceeded messages in the manner described above, but I believe this is the case (and it certainly would make sense.) See the topic discussing traceroute for further information.


Previous Topic/Section
ICMPv6 Packet Too Big Messages
Previous Page
Pages in Current Topic/Section
1
2
Next Page
ICMPv6 Parameter Problem Messages
Next Topic/Section

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!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



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.