Discontiguous network with EIGRP and auto-summary enabled

[Reprovoid]

Hi.I've set up a simple 3 router network In PT with EIGRP (auto-summary enabled).All three routers are In the 10.0.0.0 classful network.

  The thing I don't understand Is , even though the sh ip route gives two routes for the 10.0.0.0 network on each router , It's still finding the correct route to each Lan.

Router A

10.0.0.0/8 is variably subnetted, 6 subnets, 2 masks

D       10.0.0.0/30 [90/21024000] via 10.0.2.2, 00:11:59, Serial0/0

                    [90/21024000] via 10.0.1.1, 00:11:35, Serial0/1

C       10.0.1.0/30 is directly connected, Serial0/1

C       10.0.2.0/30 is directly connected, Serial0/0

C       10.0.3.0/24 is directly connected, FastEthernet0/0

D       10.0.4.0/24 [90/20514560] via 10.0.2.2, 00:11:59, Serial0/0

D       10.0.5.0/24 [90/20514560] via 10.0.1.1, 00:11:35, Serial0/1

Why Is EIGRP still working correctly In a discontiguous network with auto-summary enabled? I don't understand why the 10.0.4.0 and 10.0.5.0 are advertised.

I've attached the PT file.I would appreciate any assistance.

[John Blakley · Accepted solution]

Auto summary works only at classful boundaries. Since all of your networks are in the 10.0.0.0/8 subnet, they'll be advertised as there full subnet with no summarization because they don't cross a boundary. Try creating a loopback interface on 1 of your routers in the 172.x.x.x/24 subnet and then advertise it and you should see it summarized as 172.x.x.x/16.

HTH,

John

[Reprovoid]

Thanks! It makes sense now.