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)

Previous Topic/Section
Proxy ARP
Previous Page
Pages in Current Topic/Section
1
2
Next Page
TCP/IP Address Resolution For IP Version 6
Next Topic/Section

TCP/IP Address Resolution For IP Multicast Addresses
(Page 2 of 2)

Dealing With Multiple IP Addresses Mapped To One Multicast Hardware Address

Of course, there are 28 unique bits in IP multicast addresses, so this is a “bit” of a problem. J What it means is that there is no unique mapping between IP multicast addresses and Ethernet multicast addresses. Since 5 of the 28 bits of the multicast group cannot be encoded in the Ethernet address, 32 (25) different IP multicast addresses map onto each possible Ethernet multicast address. In theory, this would be a problem, but in practice, it isn't. The chances of any two IP multicast addresses on a single network mapping to the same Ethernet multicast address at the same time are pretty small.

Still, it is possible that two IP multicast groups might be in use on the same physical network and might map to the same data link layer multicast address. For this reason, devices must not assume that all multicast messages they receive are for their groups; they must pass up the messages to the IP layer to check the full IP multicast address to make sure they really were supposed to get the multicast datagram they received. If they accidentally get one that was intended for a multicast group they are not a member of, they discard it. This happens infrequently so the relative lack of efficiency is not a large concern.

 


Previous Topic/Section
Proxy ARP
Previous Page
Pages in Current Topic/Section
1
2
Next Page
TCP/IP Address Resolution For IP Version 6
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.