Eigrp - what happens after network command is issued

Here is EIGRP message

As soon as you configure network command on eigrp, following things happen in the given order:

Step 1. Hellos are sent.

Step 2. Receive Update.

Step 3. Run the dual and install the best route for the network learned in 2nd step.

Step 4. Send update about that interface.

An important observation here is that first of all, the above 4 steps are executed for directly connected networks.

You must be knowing this..i guess..

But notice their order..

Suppose there are two routers R1 and R2 connected via a serial link

Suppose there is a fast ethernet on each of the router R1 and R2..

Let the serial interfaces be named as R1S and R2S.

Let the fast ethernet interfaces be named as R1F and R2F

So R1 and R2 are connected via R1S and R2S...

As soon as u configure the network command, following things happen on Router R1..

a) Hello sent to R1F

b) Received update from R1F about that network

c) Run Dual and calculate the best path with the available data and feasible successor for the network learnt in step b. Enter the successor in routing table.

So you see, although local networks are already in the routing table, yet DUAL recalculates the best path and recreate the routing table with that network ..

d) Send update about network of R1F

"" At this stage ROUTING TABLE IS CREATED ( With one fastethernet network )...although Hellos are YET TO BESENT TO serial interface R1S. """

e) Hello sent to R1S

f) Received update from R1S about that network

g) Run Dual and calculate the best path and feasible successor for the network learnt in step f. Enter the successor in routing table.

h) Send update about network of R1S

After the above steps, neighbour adjancency is established with R2 if all the parameters are okay..

SO IT MEANS HELLOS ARE NOT IMMEDIATELY SENT ON ALL THE APPROPRIATE INTERFACES..

It is sent on one interface and then above 4 steps get executed in the above order.

Then hello is sent on 2nd interface and then again above 4 steps get executed in the given order.

Similar process goes on for the other interfaces that are enabled for receiving and sending EIGRP updates.

So routing table is created (though it is not complete) BEFORE hellos are sent out all the appropriate interfaces.

ref.:https://cisco.hosted.jivesoftware.com/message/5596