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I'm new to network engineering. Currently I'm studying a few routing protocols.

However, when I'm studying RIP. There is a small thing that is bothering me. I wasn't sure if RIP sends all its routing table to its neighbors or just sends downed route with metric of 16.

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When in doubt, you should check the RFC (RFC 2453, RIP Version 2, Section 3.10.1, Triggered Updates):

3.10.1 Triggered Updates

Triggered updates require special handling for two reasons. First, experience shows that triggered updates can cause excessive load on networks with limited capacity or networks with many routers on them. Therefore, the protocol requires that implementors include provisions to limit the frequency of triggered updates. After a triggered update is sent, a timer should be set for a random interval between 1 and 5 seconds. If other changes that would trigger updates occur before the timer expires, a single update is triggered when the timer expires. The timer is then reset to another random value between 1 and 5 seconds. A triggered update should be suppressed if a regular update is due by the time the triggered update would be sent.

Second, triggered updates do not need to include the entire routing table. In principle, only those routes which have changed need to be included. Therefore, messages generated as part of a triggered update must include at least those routes that have their route change flag set. They may include additional routes, at the discretion of the implementor; however, sending complete routing updates is strongly discouraged. When a triggered update is processed, messages should be generated for every directly-connected network. Split Horizon processing is done when generating triggered updates as well as normal updates (see section 3.9). If, after Split Horizon processing for a given network, a changed route will appear unchanged on that network (e.g., it appears with an infinite metric), the route need not be sent. If no routes need be sent on that network, the update may be omitted. Once all of the triggered updates have been generated, the route change flags should be cleared.

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