EIGRP FD and FS process

jsb515

can anyone help me further understand how EIGRP finds a FD and FS? I read it in Odom's book and it kinda left me a tad bit confused on how he explained it.

here is a copy and paste out of my home lab that is currently running EIGRP. Looking at this who can tell me what the FD and FS are and how did you know?

From what it looks like the 281600 is the FD via the connected Ethernet0 interface, and the FS is the 192.168.2.0 network because of the 2169856 is lower then the FD. This correct understanding?

Copy and Past from Router1
IP-EIGRP Topology Table for process 1


Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - Reply status

P 192.168.1.0/24, 1 successors, FD is 281600
via Connected, Ethernet0
P 192.168.2.0/24, 1 successors, FD is 2195456
via 192.168.1.2 (2195456/2169856), Ethernet0
P 192.168.3.0/24, 1 successors, FD is 2323456
via 192.168.1.2 (2323456/2297856), Ethernet0


Copy and Past from Router2
IP-EIGRP Topology Table for AS(1)/ID(192.168.2.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status

P 192.168.1.0/24, 1 successors, FD is 28160
via Connected, FastEthernet0/0
P 192.168.2.0/24, 1 successors, FD is 2169856
via Connected, Serial0/0
P 192.168.3.0/24, 1 successors, FD is 2297856
via 192.168.2.2 (2297856/128256), Serial0/0


Copy and Past from Router3
IP-EIGRP Topology Table for AS(1)/ID(192.168.3.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status

P 192.168.1.0/24, 1 successors, FD is 2172416
via 192.168.2.1 (2172416/28160), Serial0/2
P 192.168.2.0/24, 1 successors, FD is 2169856
via Connected, Serial0/2
P 192.168.3.0/24, 1 successors, FD is 128256
via Connected, Loopback1

atorven

Your kind of looking at this the wrong way, those successors that your seeing are for different networks so they are calculated independent of each other, to see the whole picture run a sh ip eigrp topology all-links, this will show you all the other routes that aren't successors.

jsb515

so for Router 1, what it is saying is to get to the 192.168.2.0 network the best FD is by using the 192.168.1.2 via E0 interface. There is is FS because one is not listed. This correct?

atorven

To use your example, Router 1 is saying "My best route to get to 192.168.2.0/24 is through 192.168.1.2 which I can get to using Ethernet0, the total cost of this route from my perspective is 2195456, my neighbour is telling that it costs him 2169856 to get to the same network; So to get my total cost I need to add up the cost of getting to my neighbour + what my neighbour is telling me it costs him"
HTH