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!

Read offline with no ads or diagram watermarks!
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  TCP/IP Routing Protocols (Gateway Protocols)
                9  TCP/IP Interior Routing Protocols (RIP, OSPF, GGP, HELLO, IGRP, EIGRP)
                     9  TCP/IP Routing Information Protocol (RIP, RIP-2 and RIPng)
                          9  RIP Version-Specific Message Formats and Features

Previous Topic/Section
RIP Version-Specific Message Formats and Features
Previous Page
Pages in Current Topic/Section
1
2
3
Next Page
RIP Version 2 (RIP-2) Message Format and Features
Next Topic/Section

RIP Version 1 (RIP-1) Message Format
(Page 2 of 3)

RIP-1 Message Format

The basic message format for RIP-1 is described in Table 120 and illustrated in Figure 176.


Table 120: RIP Version 1 (RIP-1) Message Format

Field Name

Size (bytes)

Description

Command

1

Command Type: Identifies the type of RIP message being sent. A value of 1 indicates an RIP Request, while 2 means an RIP Response. Originally, three other values and commands were also defined: 3 and 4 for the Traceon and Traceoff commands, and 5 reserved for use by Sun Microsystems. These are obsolete and no longer used.

Version

1

Version Number: Set to 1 for RIP version 1.

Must Be Zero

2

Reserved: Field reserved; value must be set to all zeroes.

RIP Entries

20 to 500, in increments of 20

 



Figure 176: RIP Version 1 (RIP-1) Message Format

The RIP-1 message format can contain up to 25 RIP Entries. Here, RIP Entry #1 is shown here with each of its constituent subfields.

 


If you're like me, the first thing that comes to mind looking at this message format is this: what's with all the extra space? I mean, we have four different fields that are reserved (must be zero), and even most of the other fields are larger than they need to be (a metric of 1 to 16 needs only 4 bits, not 32.) The command type and version number could easily have been made only 4 bits each as well (if not less.) And why bother having a two-byte field to identify the address type when we are only going to deal with IP addresses anyway?

This seeming wastefulness is actually an artifact of the generality of the original RIP design. The protocol was intended to be able to support routing for a variety of different internetworking protocols, not just IP. (Remember that it wasn't even originally developed with IP in mind.) So, the Address Family Identifier was included to specify address type, and RIP entries were made large enough to handle large addresses. IP only requires 4 bytes per address so some of the space is not used.


Previous Topic/Section
RIP Version-Specific Message Formats and Features
Previous Page
Pages in Current Topic/Section
1
2
3
Next Page
RIP Version 2 (RIP-2) Message Format and Features
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.