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Subnetting Question

Titiboi5542
Level 1
Level 1

I set up very simple network. The first link was a point to point link with the address 10.0.0.0/30. I then had a link with 3 devices so used the subnet 10.0.0.8/29. Two routers could then ping the third and the third could ping them, but they couldn't ping each other. I'm sure the answer is very obvious to this question and I know its not best practice, but why didn't this set up work? 

 

I changed the second segment to a 10.0.1.0/24 subnet and it worked fine. 

10 Replies 10

Hello

what was the addressing you gave to these rtrs - was the subnet address correct on all three devices - i assume they were connected all via a switch 

 

Also as they were all on the same subnet the rtrs didn’t require a default gateway or default route 

 

res

paul


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Paul

Hi Thank you for the response.

 

The routers in question are all in the same subnet. Both Routers 3 and 4 can ping router 2. Router 2 can ping 3 and 4. 

 

However, router 3 and 4 cannot ping each other.

 

Ping from router 3 to 4:

Reply to request 0 from 10.0.0.9 received 12 ms

Reply to request 1 from 10.0.0.9 received 10 ms

Reply to request 2 from 10.0.0.9 received 12 ms

etc....

 

Ping from router 4 to 3:

....... timed out...

Hello,

 

provide a schematic drawing of what your topology looks like, including what is connected to what, and which IP addresses are used on which links.

Hi Thank you for the response. The routers in question are all in the same subnet. Both Routers 3 and 4 can ping router 2. Router 2 can ping 3 and 4. However, router 3 and 4 cannot ping each other. Ping from router 3 to 4: Reply to request 0 from 10.0.0.9 received 12 ms Reply to request 1 from 10.0.0.9 received 10 ms Reply to request 2 from 10.0.0.9 received 12 ms etc.... Ping from router 4 to 3: ....... timed out...

Hello,

 

check the routing tables: R1 only knows network 10.0.0.0/30, and R3 and R4 only know network 10.0.0.8/29. In order for all networks to be reachable, you need to run either a static default route on ech router, or a routing protocol. 

 

So either:

 

R1

ip route 0.0.0.0 0.0.0.0 10.0.0.2

 

R3

ip route 0.0.0.0 0.0.0.0 10.0.0.9

 

R4

ip route 0.0.0.0 0.0.0.0 10.0.0.9

 

or on each router:

 

router rip

version 2

network 0.0.0.0

no auto-summary

A default route shouldn't be needed to communicate with a route on the same subnet though correct? The router 10.0.0.9 can ping 10.0.0.9 but not 10.0.0.11 even though they are both connected to the same switch.

sorry I meant the router on 10.0.0.10 can ping 10.0.0.9 but not 10.0.0.11

Hello,

 

post the configurations of your routers...

It seems to me that Georg is trying to solve a different problem. He is concerned about Router 1 access to Router 3 and 4. While I agree that this is a valid concern, it is not what the original post is asking about. The question here is why Router 3 and Router 4 can not communicate. To answer this we need more information. We especially need to understand how Routers 2, 3, and 4 are connected. If this turns out to be a Frame Relay connection then it is likely that the issue is that Router 3 does not have a mapping of IP to DLCI for Router 4 (and similarly lacking a mapping on Router 4 for Router 3). If the connection is a switch, then we have a different issue. I agree with Georg that having the config of the routers will be very helpful.

 

HTH

 

Rick

HTH

Rick

I agree with Richard. For the sake of verification I recreated your setup in GNS3, and with Ethernet interfaces and IP addresses 10.0.0.9/28, 10.0.0.10/28, and 10.0.0.11/28 configured on the interfaces, every IP address can ping the respective other ones.

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