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dsr_deep1
Beginner

VPN between two sites using same subnet

Hi there,

I am kind of new to firewalls,  someone plz help, lets say my main office and branch office  has same ip subnet ranges and i came to know that ipsec doesnot  work in that situation. what am i supposed to do to make it work. do i have to configure some kind of  natting or ?????? is there any alternative, plz kindly help.

6 REPLIES 6
Jouni Forss
Mentor

Hi,

Both sites should do NAT to their local networks before forwarding traffic to the L2L VPN between the sites.

Otherwise the traffic simply wont be forwarded correctly.

Configurations naturally depends on the devices and the software running on them.

- Jouni

Thanks for your quick reply. if am not worng we basically we use nat 0 with vpns to avoid packets being  send to some other destination. am kind of confused now, what happens if we enable netting in this situation. lets say we have 172.168.4.0 subnet on both sites and we are using ASA 5520. if possible plz provide me some url link where this situation and configuration is explained properly, tried over internet but couldn't find good explanation.THNX

Hi,

Here is one

http://www.cisco.com/en/US/products/ps6120/products_configuration_example09186a0080b37d0b.shtml

It basicly gives you a configuration example with 2 ASA which have the same LAN networks.

Its does a Static Policy NAT on both sides and NATs the local network to some other similiar equal size network.

- Jouni

THNX

Hi,

Remember to mark the reply as the correct answer if it answered your question.

Naturally if you need some help then ask away.

- Jouni

Karsten Iwen
VIP Mentor

And never forget the better solution if one site is really a more small branch-office: If you renumber the IP-addressing in that office you won't have this ongoing pain that double-NAT causes.

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