[c-nsp] separate two directly connected networks on a Cisco 1800 series ISR?

[Martin T]

Hi,

I have a network setup where networks 192.168.1.0/24 and
192.168.2.0/24 are served by same router(Cisco 1841,
c1841-spservicesk9-mz.124-7a.bin) and while addresses in
192.168.1.0/24 are NAT -ed to inside global address 10.10.10.1, the
192.168.2.0/24 network is not NAT-ed:
http://s10.postimg.org/dsn73dzm1/test.png

I would like to deny access from 192.168.2.0/24 network to
192.168.1.0/24. For this reason I have "deny ip 192.168.2.0 0.0.0.255
192.168.1.0 0.0.0.255" ACL in inbound direction on interface facing
the 192.168.2.0/24 network:

R3#sh ip access-lists 100
Extended IP access list 100
    10 deny ip 192.168.2.0 0.0.0.255 192.168.1.0 0.0.0.255 (456 matches)
    20 permit ip any any (90 matches)
R3#


However, at the same time, one should have access from 192.168.1.0/24
network to 192.168.2.0/24 network. Because of the ACL described above,
this obviously does not work as returning packages from 192.168.2.0/24
network will have src IP from 192.168.2.0/24 network and dst IP from
192.168.1.0/24 network and will be dropped by ACL. What are the
options here? I tried to add second NAT setup which should change the
src address of those packets which are from 192.168.1.0/24 AND
destined to 192.168.2.0/24. Configuration for this was following:

interface Vlan5
 description -> T42 eth0
 ip address 192.168.1.1 255.255.255.0
 ip nat inside
end
!
interface Vlan10
 description -> T60
 ip address 192.168.2.1 255.255.255.0
 ip access-group 100 in
 ip nat outside
end
!
ip nat inside source list 102 interface Vlan10 overload
!
access-list 102 permit ip 192.168.1.0 0.0.0.255 192.168.2.0 0.0.0.255
!

Such approach seems to work. If I send an ICMP "echo request" package
from 192.168.1.2 to 192.168.2.2, then it's NAT -ed and for 192.168.2.2
host this ICMP "echo request" appears to be from 192.168.2.1.


In addition, I tried few setups with policy based routing, but
eventually none of those worked.


What is the best approach here? Stick with this NAT solution described
above? Something completely different to separate two networks behind
the same router?



regards,
Martin