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 and the network between the router and the stations being the 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      YES NVRAM  up                    up
FastEthernet0/1     YES NVRAM  up                    up

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 to network

S* [1/0] via is variably subnetted, 2 subnets, 2 masks
C is directly connected, FastEthernet0/0
L is directly connected, FastEthernet0/0 is variably subnetted, 2 subnets, 2 masks
C is directly connected, FastEthernet0/1
L 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, mask of and default gateway of

Now this is where it gets weird: From the router's CLI I can successfully ping,, and From the test PC I can successfully ping only and When trying to ping 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?


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.

2 Answers 2


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


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 /24 network is reachable via, or doesn't have a NAT policy for the .10.x subnet.

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