1

Does NAT affect other networks on the router?

If I have two subnets on a router and I want to access the non-natted network through natted interface. Will it have any affect at all?

I.e.will I have any trouble accessing the normal non-natted network from r1?

r1
|
nat outside network
|
r2-----------------------(normal network non-natted)
|
|
nat inside network

1
  • 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 10, 2017 at 3:19

1 Answer 1

3
 r1
 |
 nat outside network
 |
 r2-----------------------(normal network non-natted)
 |
 |
 nat inside network

... will I have any trouble accessing the normal non-natted network from r1?

Assuming you are routing on all devices correctly, R1 can access the normal network non-natted. To be explicit...

Assume:

  • nat outside network is 198.51.100.0/24
  • (normal network non-natted) is 203.0.113.0/24
  • nat inside network is 10.1.1.0/24
  • R1 has a route to 203.0.113.0/24
  • R2 has a routes to anything on or behind R1

Packet flow:

If R1 receives a packet for 203.0.113.50, it will forward the packet to R2. R2 has a connected interface for 203.0.113.0/24, so it looks up the layer2 adjacency information for 203.0.113.501 and forwards R1's packet to normal network non-natted. As long as 203.0.113.50 has a default pointing to R2, and R2 can reach the IP subnet which originally sourced the traffic behind R1, then there are no problems.

In summary, NAT is a local operation between two interfaces on the same router / firewall. NAT does not affect the reach-ability of interfaces that are not participating in NAT.


1using ARP tables, if normal network non-natted is Ethernet.

2
  • Is this "bridging" the connection?
    – HAL
    Mar 10, 2014 at 13:32
  • 1
    The traffic described in my answer is routed Mar 10, 2014 at 13:34

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.