For the purpose of communication, the EIGRP routing protocol does not make use of either TCP or UDP, just like other routing protocols. For the purpose of communicating with other EIGRP-speaking routers, an EIGRP router employs the RTP protocol.
Reliable Transport Protocol is referred to as RTP. It is a proprietary protocol used by Cisco. It was created by Cisco to offer dependable communication between two devices. In order to guarantee prompt and dependable packet delivery, it makes use of both multicasts and unicasts.
This is because RTP only sends one packet at a time. Due to the fact that it only transmits a single packet at a time, it does not make use of windowing or any other congestion control function. Furthermore, it is compatible with both multicast and unicast transmission systems.
How does RTP work with EIGRP?
For EIGRP to talk to other EIGRP-speaking routers on the network, it uses RTP. During the application of EIGRP, RTP is in charge of making sure that EIGRP packets are delivered in the right order by using sequence and acknowledge numbers.
In EIGRP, each router knows who its other routers are. When an EIGRP router sends a multicast, it keeps track of the neighbors who have answered by making a list. Unicasts are used by the EIGRP router to send the same data again if it doesn’t hear back from a neighbor through multicast. It says the router is dead if it doesn’t hear back from the neighbor after 16 unicast tries. There is a name for this process: reliable multicast.
EIGRP gives each file a sequence number so that it can be tracked. Sequencing helps routers get rid of old or unnecessary packets and packets that are out of order.
For each neighbor, RTP keeps a retransmission table. It keeps track of all the reliable packets that were sent but not recognized before the Retransmission Time Out (RTO) in this table. A record is made in the table for each reliable packet that RTP sends. The entry contains the RTO timer. RTP will send the same copy of the reliable packet again if the RTO timer runs out before an ACK packet is received. This process will be repeated by RTP until the neighbor’s hold time in the neighbor table runs out. If a neighbor’s hold time in the neighbor table runs out, EIGRP takes that neighbor out of the neighbor table.
Types of EIGRP packets
There are five packet types used by EIGRP. The update, query, reply, hello, and acknowledgement types are among them. Let’s talk about these kinds.
Update
You can find the latest routing information or updates in an Update packet. Two EIGRP routers establish a neighbor relationship by exchanging routing information through update packets. After establishing a neighbor relation, the only time they communicate about changes is through update packets.
Whether sending an update packet via multicast or unicast, EIGRP always employs reliable methods. If you want to notify all of your neighbors at once, you can use EIGRP’s multicast feature. If you only want to notify one neighbor, you can use its unicast feature.
An acknowledgment is always required by EIGRP for each update packet, regardless of the method it employs to send them.
