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In my network journey, I'm studying static routes now (I know that isn't used in large environments, but just studies).

I made this topology in GNS3, and I'm wondering if some points are correct. enter image description here

PS: The .x are the IP of the interface.

The routing tables are:

**R1**
     172.16.0.0/24 is subnetted, 1 subnets
C       172.16.1.0 is directly connected, FastEthernet0/0
     10.0.0.0/30 is subnetted, 2 subnets
S       10.0.0.0 [1/0] via 10.0.1.2
C       10.0.1.0 is directly connected, FastEthernet1/0
C    192.168.1.0/24 is directly connected, FastEthernet0/1
S    192.168.2.0/24 [1/0] via 10.0.1.2
S    192.168.3.0/24 [1/0] via 10.0.0.2


**R2**
     10.0.0.0/30 is subnetted, 2 subnets
C       10.0.0.0 is directly connected, FastEthernet0/0
C       10.0.1.0 is directly connected, FastEthernet1/0
S    192.168.1.0/24 [1/0] via 10.0.1.1
C    192.168.2.0/24 is directly connected, FastEthernet0/1
S    192.168.3.0/24 [1/0] via 10.0.0.2


**R3**
     10.0.0.0/30 is subnetted, 2 subnets
C       10.0.0.0 is directly connected, FastEthernet0/0
S       10.0.1.0 [1/0] via 10.0.0.1
S    192.168.1.0/24 [1/0] via 10.0.1.1
S    192.168.2.0/24 [1/0] via 10.0.0.1
C    192.168.3.0/24 is directly connected, FastEthernet0/1

I'm wondering, for the R3 to reach the subnet 192.168.1.0, I do need to specify static routes for 10.0.1.0/30 AND 192.168.1.0?. Same goes for the R1 reach 192.168.3.0... Is this the way it works?

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  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin
    Aug 9 '17 at 1:56
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If your plan is to replicate the insanity of a dynamic routing protocol, then you're well on your way. :-)

No sane network engineer would ever add static routes to non-local endpoints. Your 192.168.3.0/24 on R1, for example, is routed to 10.0.0.2, which is not connected to it. In order to install that route in the table, a route to 10.0.0.2 (10.0.0.0/30) must exist. This just makes reading your config a pain. The router will make multiple passes over the RIB to build the active route table. (in this case, it'll sync in a fraction of a second.)

Textbook answer: The next-hop must be reachable for the route to be installed.

(Dynamic routing protocols may do this for other reasons. Humans tend to avoid it because it generates real headaches.)

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This is one way to do it however not best practice, two things; 1/ If your router only has one connection outside of its LAN side in your case R3 only has fa0/0 which is connected to 10.0.0.0/30. You can just have a static default route 0.0.0.0 0.0.0.0 pointing to the next hop of 10.0.0.1 on R2. Treat R3 as a stub unless you add more interfaces.

2/ the static route you have configured: S 192.168.3.0/24 [1/0] via 10.0.0.2 should NEVER be used in real environment, pointing a static route to a local IP address rather than a directly connected next-hop will cause excessive ARP, each time a packet is sent out this interface in turn resulting in high CPU. Might not see this in GNS3 as it is all software processed in CPU anyway but on a real router (if Cisco) this will not be CEF switched.

Also as you said so many static routes is not a good idea, if you want to advertise your LAN networks just use a routing protocol...

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  • Ok, got the R3 issue. But about the second one, for the real environment, I should add one more interface in the R3 and make it directly connected to R1? Aug 30 '14 at 1:46
  • That was just hypothetical if you had another interface and doesnt need to be connnected to r1 just make sure you point the static route to r2's ip address not r3 (itself) Aug 30 '14 at 2:00
  • This is better now, right? i.imgur.com/M1LZkQG.png Now R2 and R3 is connected to the get-to-internet router. Aug 30 '14 at 2:18
  • 1
    Yep much better Aug 30 '14 at 3:40
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    Routing doesn't happen by ARP -- unless you route to an ethernet interface. (DON'T!)
    – Ricky
    Aug 30 '14 at 5:51

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