I defined 3 routers connected between them with serial links and I connected to each router one LAN subnet:
LAN R1: 188.8.131.52/24
LAN R2: 184.108.40.206/24
LAN R3: 220.127.116.11/24
I configured RIP-v2 and for each router I set to be advertised only its LAN subnet:
R1: network 18.104.22.168
R2: network 22.214.171.124
R3: network 126.96.36.199
But I didn't see any RIP update at all from neither of the routers on neither of their interfaces (nor on their 2 serial itf. nor on the fastethernet itf.).
Q1a: Why the LAN subnets were not advertised ?
Only after I added the other 2 networks to be advertised:
R1: network 188.8.131.52, network 184.108.40.206, network 220.127.116.11
R2: network 18.104.22.168, network 22.214.171.124, network 126.96.36.199
R3: network 188.8.131.52, network 184.108.40.206, network 220.127.116.11
the RIP updates started to be sent (they contained as well the LAN subnets).
Q1b: So any idea why this behavior ?
Also I observed by using both:
'show ip route' and 'debug ip rip events'
that the routes advertised through RIP were all with /8, not with /24.
Q2: Why this behavior, as version 2 of RIP is set on all the routers (and the RIP updates are correctly sent to 18.104.22.168 confirming so that indeed RIP-v2 is used) ?
Next I changed the LAN subnets as follows:
LAN R1: 22.214.171.124/26
LAN R2: 126.96.36.199/25
LAN R3: 188.8.131.52/26
and set as well in R2 and R3 the network 184.108.40.206 to be advertised.
I observed that still the updates and the routes were with /8 as before.
However, surprisingly for me, the ping was working between the LANs...and I don' understand how it could work.
In R1 for instance I have the following routes for 220.127.116.11 network:
R 18.104.22.168/8 [120/1] via 22.214.171.124, 00:00:18, Serial3/0
[120/1] via 126.96.36.199, 00:00:04, Serial2/0
C 188.8.131.52/26 is directly connected, FastEthernet0/0
Q3: So how the router R1 knows where to route a packet with a destination for ex. 184.108.40.206 ? To Serial 3/0 or to Serial 2/0 ?
There's ambiguity in-here, isn't there?
I even disabled the interface between R2 and R3, but ping from LAN1 was still working to LAN2 and LAN3.
Could anyone help me uncover this mystery?
PS: All the tests were done with PacketTracer 5, so on a simulated environment.