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I have Router 1 and Router 2. For R1 I have 1.1.1.1 with /24 mask, for R2 I have 1.1.2.1 with /24 mask. R2 is connected to R1 interface with 1.1.1.2 address. Following image shows my topology https://i.stack.imgur.com/dEoGA.png

Routing table on R1:

1.1.2.0         255.255.255.0   1.1.1.2
1.1.1.0         255.255.255.0   0.0.0.0
81.190.224.0    255.255.240.0   0.0.0.0
0.0.0.0         0.0.0.0         81.190.224.1

Routing table on R2:

1.1.2.0         255.255.255.0   0.0.0.0
1.1.1.0         255.255.255.0   0.0.0.0
0.0.0.0         0.0.0.0         1.1.1.1

What I have a problem with? As there is no problem with pinging PC1 from PC2, it is not possible to communicate anyone in R2's subnet from R1's. (ping is just an example, there is no problem with machines itself)

R1 also cannot communicate R2 on it's internal ip (1.1.2.1), but using 1.1.1.2 it can.

What am I doing wrong in this case?

Mateusz Kowalski
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  • Your configuration seems to be okay. The cause of the problem should be some other. I see the probabliest cause if you hadn't switched off NAT on R2. Can you test somewhere on R1 network, from which source ip are coming the ping packets originated from the R2 network? – peterh Feb 13 '14 at 09:32
  • Indeed, on R2 NAT is enabled. But why does it impact on connectivity between PC1 and R2? – Mateusz Kowalski Feb 13 '14 at 09:37
  • Because this is what we call NAT. If you want a NATted R2 network, that means that you make impossible the direct contact of the machines of the R2 network from the R1 network. In this case, you don't need even the 1.1.2.0/24 route on R1. If you want a transparent network, where everybody can contact everybody, you should switch off NAT on R2. – peterh Feb 13 '14 at 09:43
  • R1 should communicate R2 with its external IP (1.1.1.2) and not with its internal, also exactly contradictory how it works. Its cause is probably in some firewall settings on R2. – peterh Feb 13 '14 at 09:45
  • Your routing table misses the devices/interfaces for each of the entries. But when we accept they are correct, and the PCs all have default routes to their nearest router (only), then the problem must be in the area of ipfilter or nat rules. I would start with removing all of them and testing local only. – eckes Oct 09 '14 at 02:58

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