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 Fundamentals and General Operation

RIP Route Determination Algorithm and Metric 1 2 3 RIP Protocol Limitations and Problems

RIP is a protocol for exchanging routing information, so its operation can best be described in terms of the messages used to exchange this information, and the rules for when messages are sent. The RIP software in each router sends messages and takes other actions both in reaction to certain events and in response to triggers set off by timers. Timers are also used to determine when routing information should be discarded if not updated.

Communication between RIP software elements in routers on an internetwork is accomplished through the use of RIP messages. These messages are sent using the User Datagram Protocol (UDP), with reserved UDP port number 520 for RIP-1 and RIP-2, and 521 for RIPng. Thus, even though RIP is considered part of layer three like other routing protocols, it behaves more like an application in terms of how it sends messages. The exact format of the message is version-dependent, and all three formats (for RIP, RIP-2 and RIPng) are described in detail in their own section. RIP messages can be either sent to a specific device, or can be sent out for multiple devices to receive. If directed to one device they are sent unicast; otherwise, they are either broadcast (in RIP) or multicast (RIP-2 and RIPng).

There are only two basic message types for all three versions of RIP:

• RIP Request: A message sent by a router to another router asking it to send back all or part of its routing table.
  
  
• RIP Response: A message sent by a router containing all or part of its routing table. Note that despite the name, this message is not sent just in response to an RIP Request message, as we will see. So it's not really that great a name… oh well.

RIP Route Determination Algorithm and Metric 1 2 3 RIP Protocol Limitations and Problems