EIGRP question related to the 16 retry rule.

adam-b

Hello All,

It is my understanding that EIGRP will declare a neighbor dead if an ACK is not recieved in response to any of the 16 queries that it sends. Does this rule apply to updates and replies as well? So for example, if a router does not recieve an ack to a query reply that it sends, then will it send the reply 15 more times and then declare the neighbor dead? Or does this rule only apply to Query packets?

Thanks for the clarification,

Adam

jovan88

anyone can correct me if I'm wrong, I believe the 16 resend rule applies to all reliable RTP packets.

Forsaken_GA

From Routing TCP/IP, Vol. 1

'If any packet is reliably multicast and an ACK is not received from a neighbor, the packet will be transmitted as a unicast to that unresponding neighbor. If an ACK is not received after 16 of these unicast transmissions, the neighbor will be declared dead'.

Dubuku57

adam-b wrote: »

Hello All,

It is my understanding that EIGRP will declare a neighbor dead if an ACK is not recieved in response to any of the 16 queries that it sends. Does this rule apply to updates and replies as well? So for example, if a router does not recieve an ack to a query reply that it sends, then will it send the reply 15 more times and then declare the neighbor dead? Or does this rule only apply to Query packets?

Thanks for the clarification,

Adam

From McGraw Hill CCNA Study Guide 640-802 Apr 2008,

"...EIGRP, like OSPF, is connection-oriented: certain
EIGRP messages sent by a router will cause it to expect an acknowledgment (ACK) from the destination(s). Here are the message types for which an EIGRP router expects an ACK back:

■ Update Contains a routing update

■ Query Asks a neighboring router to validate routing information

■ Reply Responds to a query message

If an EIGRP router doesn’t receive an ACK from these three packet types,

the router will try a total of 16 times to resend the information. After this, the router declares the neighbor dead. When a router sends a hello packet, however, no corresponding ACK is expected in return."

Hope this helps.

auos

Hi,
If any one want to understanding the (Hello, ACK, Query, Replay and Update) Messages I extremely recommended to read (Authorized Self-Study Guide BSCI 642-901 3rd Edition), because it is explain these messages in more efficient way.

BR,
Auos.

adam-b

Thanks for your replies guys. This was an area of confusion for me...thanks for clearing up.