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 4 (ICMPv4) Error Message Types and Formats

Previous Topic/Section
ICMPv4 Time Exceeded Messages
Previous Page
Pages in Current Topic/Section
12
3
Next Page
ICMPv4 Parameter Problem Messages
Next Topic/Section

ICMPv4 Redirect Messages
(Page 3 of 3)

Limitations of Redirect Messages

I must emphasize that ICMP Redirect messages are not a mechanism by which the general routing process in IP is implemented; they are a support function only. They are a convenient way for hosts to be given information about routes by local routers, but are not used to communicate route information between routers.

This means that a Redirect can tell a host to use a more efficient first-hop router, but cannot tell a router to use a more efficient second-hop router. In our example above, suppose that in addition to the connections mentioned, R2 is connected to R3 and R4 as shown in Figure 143. R2 sends the datagram in question to R3, which realizes it needs to send to R4, a router already directly connected to R2. R3 cannot send a Redirect to R2 telling it to use R4 next time. The messages are simply not designed for this purpose—remember that ICMP messages always go back to the source of the original datagram, which would not be R2 in this case. Such inefficiencies must be resolved using routing protocols.

Key Concept: ICMPv4 Redirect messages are used by a router to inform a host of a preferred router to use for future datagrams sent to a particular host or network. They are not used to alter routes between routers.



Previous Topic/Section
ICMPv4 Time Exceeded Messages
Previous Page
Pages in Current Topic/Section
12
3
Next Page
ICMPv4 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.