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!

The whole site in one document for easy reference!
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 Network Interface / Internet "Layer Connection" Protocols
           9  Address Resolution and the TCP/IP Address Resolution Protocol (ARP)
                9  Address Resolution Concepts and Issues

Previous Topic/Section
Dynamic Address Resolution
Previous Page
Pages in Current Topic/Section
1
2
Next Page
TCP/IP Address Resolution Protocol (ARP)
Next Topic/Section

Dynamic Address Resolution Caching and Efficiency Issues
(Page 2 of 2)

Other Enhancements to Dynamic Resolution

Other enhancements are also possible to the basic dynamic resolution scheme. Let's consider again our example of sending a request to the Internet. We send a request that needs to go to our local router, so we resolve its address and send it the request. A moment later the reply comes back to the router to be sent to us, so the router needs our address. Thus, it would have to do a dynamic resolution on us even though we just exchanged frames. Again: stupid. Instead, we can improve efficiency through cross-resolution; when device A resolves the address of device B, device B also adds the entry for device A to its cache.

Another improvement can be made too. If you think about it, the devices on a local network are going to talk to each other fairly often, even if they aren't chatting right now. If A is resolving B's network layer address, it will broadcast a frame that devices C, D, E and so on all see. Why not have them also update their cache tables with resolution information that they see, for future use?

These and other enhancements all serve to cut down on the efficiency problems with dynamic address resolution. They combine to make dynamic resolution close enough to direct mapping in overall capability that there is no good reason not to use it. Once again, you can see some more particulars of this in the topic that describes the TCP/IP ARP protocol's caching feature.

Incidentally, one other performance-improving idea sometimes is brought up in this discussion: instead of preceding a datagram transmission with an extra broadcast step for address resolution, why not just broadcast the datagram and be done with it? We actually could do this, and if the datagram were small enough it would be more efficient. Usually, though, datagrams are large, while resolution frames can be quite compact; it makes sense to do a small broadcast and then a large unicast rather than a large broadcast. Also, suppose we did broadcast this one datagram: what about the next datagram and the one after that? Each of these would then need to be broadcast also. When we do a resolution, with caching, we need to broadcast only once in a while instead of continually.

 


Previous Topic/Section
Dynamic Address Resolution
Previous Page
Pages in Current Topic/Section
1
2
Next Page
TCP/IP Address Resolution Protocol (ARP)
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.