EIGRP does not rely exclusively on the use of timers for routing table maintenance; rather EIGRP uses periodic communication to perform the following:
• Dynamically learn of new routers that can join the network.
• Identify routers that become either unreachable or inoperable.
• Rediscover routers that had previously been unreachable.
The initial exchange of routing tables is accomplished with the EIGRP hello packet between neighbors. Reliable Transport Protocol
EIGRP can provide guaranteed and reliable delivery of its various packets, whereas other routing protocols rely on other mechanisms, such as time, to determine if a packet needs to be retransmitted. EIGRP uses the Reliable Transport Protocol (RTP) to provide reliable delivery of its own packets.
RTP is a transport layer (OSI Layer 4) protocol that correlates to the functions found in TCP and UDP; however, RTP is not an open protocol standard.
RTP is used to transport all EIGRP messages through an internetwork and supports both unicasting and multicasting, even simultaneously for different peers.
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