Hello Clement.
There are differing opinions as to how many and what type of EIGRP packets exist. Some refer to five, others to six. Some group Request packets and Query packets together. Some group ACK and Hello packets together (since ACK is basically an empty hello packet). Some just don’t mention Request packets. It really depends on who you ask.
Cisco’s official documentation states that there are five packet types:
* Hello/Acks
* Updates
* Queries
* Replies
* Requests
Although Cisco’s official CCNA curriculum gives the following list:
* Hello
* Acknowledgements
* Updates
* Queries
* Replies
In any case, a request packet is similar to a query packet, except for the fact that query packets are sent reliably while request packets are not. Request packets can be both unicast or multicast and are initially sent when an EIGRP router joins an EIGRP AS and requests information from neighbours.
Cisco also says that these packets are used in route server applications. A route server is a troubleshooting device within an Autonomous System that is able to view the IP routing tables of all participating routers. It can be used to determine routing faults and to correct routing malfunctions. So request packets are used for such applications.
The truth is it is not very clear, but I hope that this makes it somewhat clearer for you.
I hope this has been helpful!
Laz