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In order to have a second "backup" gateway for my company network, I tried to implement this topology:enter image description here

It is pretty straightforward, with the network between the modem and the router being the 192.168.1.0/24 and the network between the router and the stations being the 192.168.10.0/24. The actual IP addresses are the ones on the sketch.

The status of the interfaces on the router is like this:

cisco1#show ip interface brief Interface IP-Address OK? Method Status Protocol FastEthernet0/0 192.168.1.69 YES NVRAM up up FastEthernet0/1 192.168.10.69 YES NVRAM up up Serial0/0/0

The routing table is like this:

cisco1#show ip route Codes: L - local, C - connected, S - static, 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 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP + - replicated route, % - next hop override Gateway of last resort is 192.168.1.1 to network 0.0.0.0 S* 0.0.0.0/0 [1/0] via 192.168.1.1 192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks C 192.168.1.0/24 is directly connected, FastEthernet0/0 L 192.168.1.69/32 is directly connected, FastEthernet0/0 192.168.10.0/24 is variably subnetted, 2 subnets, 2 masks C 192.168.10.0/24 is directly connected, FastEthernet0/1 L 192.168.10.69/32 is directly connected, FastEthernet0/1

As you can see I have configured the modem's IP address as the gateway of last resort, so that the packets take that way towards the Internet.

I have also configured my test PC with an IP of 192.168.10.13, mask of 255.255.255.0 and default gateway of 192.168.10.69.

Now this is where it gets weird: From the router's CLI I can successfully ping 192.168.1.1, 192.168.1.69, 192.168.10.69 and 192.168.10.13. From the test PC I can successfully ping only 192.168.1.69 and 192.168.10.69. When trying to ping 192.168.1.1 from the test PC it fails.

Of course I have no Internet connectivity from the test PC.

Now, is there something I am overlooking? Why is it that I cannot connect to the internet?

UPDATE:

After some more inspection, my routing table looks really fishy. Why have the directly connected networks been broken up like that? I have never before seen The interface IP addresses mentioned in the routing table as separate "/32" directly connected subnets.

Does anyone have any idea why this is happening? I have a strong feeling this may be related to my connectivity issue.

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2 Answers 2

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As @cpt_fink already worte, the issue is the reverse route: enter image description here

Configure NAT on the Router. I found a great post about that topic: http://www.firewall.cx/cisco-technical-knowledgebase/cisco-routers/260-cisco-router-nat-overload.html

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In reverse order...

Your routing table is actually correct. The L flag means that is the IP address local to the router on that link, while the C flag means that network is attached to the router on that link.

The problem would be that your modem doesn't know that the 192.168.10.0 /24 network is reachable via 192.16.1.69, or doesn't have a NAT policy for the .10.x subnet.

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