I am preparing my ccna exam and was reading this evening through the EIGRP protocol. At a point the autor writes that if you have a discontiguous network, you have to use the "no auto-summarize" command to make it possible that the routing updates are done correctly between the routers in the AS.
I tried a small netowrk on Boson NetSim where i had 2 routers A and B connected with a serial line and a network of 10.3.1.0/24 and on one router (A) i had a network like 172.16.10.0/24 on the fa interface and on the other one (B) a network called 172.16.20.0/24.
I configured than the eigrp and i didn't use the "no auto-summarize" command. So theoreticaly if i understood everything right i wouldn't be able to ping the 172.16.10.0/24 from router B.....but it worked....i could ping it. And if i checked the routing table everything was just fine.
So my question now....Is it possible that there is a bug in the Boson NetSim software or did i understand something wrong?
Could somebody please give me some light in this matter.
As I understand the problem, you connect two routers, and their common network is 10.3.1.0/24.
Now each router has exactly one network 172.16.?.? on the other interface? What should happen is that e.g. one router summarizes his 172.16.20.0/24 network and advertises it as 172.16.0.0/ 16 (ClassB) to his neighbour.
The other router now knows about his 172.16.20.0/24 network (as C = directly connected) and 172.16.0.0/16 on the other side. He should be able to reach each network (longest match!).
To break the network try at least 3 routers. Same setup
the point is that i took basicaly the example they gave in the course. I even found the same example in a cisco press article where they explained the same thing.
i will of course also try the 3 router approch but i am still wondering why they give this example in the course book even if it is not needed to have the "no auto-summarize" command.
What they say in the book is that both routers will start sending updates like 172.16.0.0/16 and that both routers will refuse these updates since they think they know about this network and thus you will not be able to reach the net work on the other side.
here is the article i've found from cisco press....just search for "discontiguous" in the document and you will find the example i am talking about.
I've set up the example of cisco press with 2 1603 routers to have the same lab as in the book....and if i follow the configuration, i cannot ping the ethernet interface of the routers. here is the output of the ip table of Lab_A router
Lab_A#sh ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
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