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 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

RIP Version 1 (RIP-1) Message Format 1 2 3 RIPng ("RIPv6") Message Format and Features

RIP-2 Message Format

The basic message format for RIP-2 is also pretty much the same as it was for RIP-1, with the Version field of course set to 2, to clearly identify the message as being RIP-2. The real differences are in the individual RIP entries, as you can see in Table 121 and Figure 177.

Table 121: RIP Version 2 (RIP-2) 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.
Version	1	Version Number: Set to 2 for RIP version 2.
Must Be Zero	2	Reserved: Field reserved; value must be set to all zeroes.
Route Table Entries (RTEs)	20 to 500, in increments of 20

As you can see, the unused fields allow the new RIP-2 features to be implemented without changing the basic structure of the RIP entry format. This allows RIP-1 and RIP-2 messages and devices to coexist in the same network. A RIP-2 device can handle both RIP-1 and RIP-2 messages, and will look at the version number to see which version the message is. A RIP-1 device should handle both RIP-2 and RIP-1 messages the same way, simply ignoring the extra RIP-2 fields it doesn't understand.

RIP Version 1 (RIP-1) Message Format 1 2 3 RIPng ("RIPv6") Message Format and Features