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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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► Support for multicasting: R<strong>IP</strong>-2 supports the use of multicasting rather than<br />

simple broadcasting of routing annoucements. This reduces the processing<br />

load on hosts not listening for R<strong>IP</strong>-2 messages. To ensure interoperability<br />

with R<strong>IP</strong>-1 environments, this option is configured on each network interface.<br />

► Support for authentication: R<strong>IP</strong>-2 supports authentication of any node<br />

transmitting route advertisements. This prevents fraudulent sources from<br />

corrupting the routing table.<br />

► Support for R<strong>IP</strong>-1: R<strong>IP</strong>-2 is fully interoperable with R<strong>IP</strong>-1. This provides<br />

backward-compatibility between the two st<strong>and</strong>ards.<br />

As noted in the R<strong>IP</strong>-1 section, one notable shortcoming in the R<strong>IP</strong>-1 st<strong>and</strong>ard is<br />

the implementation of the metric field. R<strong>IP</strong>-1 specifies the metric as a value<br />

between 0 <strong>and</strong> 16. To ensure compatibility with R<strong>IP</strong>-1 networks, R<strong>IP</strong>-2 preserves<br />

this definition. In both st<strong>and</strong>ards, networks paths with a hop-count greater than<br />

15 are interpreted as unreachable.<br />

5.4.1 R<strong>IP</strong>-2 packet format<br />

The original R<strong>IP</strong>-1 specification was designed to support future enhancements.<br />

The R<strong>IP</strong>-2 st<strong>and</strong>ard was able to capitalize on this feature. R<strong>IP</strong>-2 developers<br />

noted that a R<strong>IP</strong>-1 packet already contains a version field <strong>and</strong> that 50% of the<br />

octets are unused.<br />

190 <strong>TCP</strong>/<strong>IP</strong> <strong>Tutorial</strong> <strong>and</strong> <strong>Technical</strong> <strong>Overview</strong>

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