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Traffice routed through Fortigate VPN does not reach hosts on another VPN

Posted on 2016-09-04
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Last Modified: 2016-09-05
Three key points:
1) Branch (Fortigate 60c with FortiOS 5.2)
2) Headquarters (Fortigate 100d with FortiOS 5.2)
3) Third-party office (unknown device)

Current status:
1) Branch and Headquarters are linked through an IPsec Tunnel ("Branch-To-Headquarters Tunnel") that works fine. Branch hosts are able to communicate with Headquarters hosts.
2) Headquarters and Third-party office are linked through an IPsec Tunnel ("Headquarters-To-3rdParty Tunnel") that works fine. Headquarters hosts are able to communicate with Third-party office hosts.

Now, I need that Branch hosts are able to communicate with Third-party office hosts through the existing tunnels, so, I have done the following:
1) Create a static route on Branch, to route all traffic to 3rd party hosts trough "Branch-To-Headquarters Tunnel"
2) I confirmed that the requests are being received, accepted on the Headquarters firewall.

However, I don't get a reply back from 3rd party.

I'm suspecting about two possible causes:
1) traffic is not being routed from Headquarters to 3rd party (I don't think so, since I only have one static route that works when communicating from Headquarters through 3rd party)
2) There's something related to NAT that is not working as expected (for instance: 3rd party is waiting from requests from Headquarters' subnet, but requests are being received from Branch's subnet). If that's the case...how can I instruct Fortigate to "treat requests originating from Branch Office, as if they were originated in Headquarters" so the 3rd party firewall would accept them?

Please refer to the attached image for clarification.

Any help on this?

Thanks,
IssueWithRouting.png
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Question by:dsuy
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3 Comments
 
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Accepted Solution

by:
Bing CISM / CISSP earned 500 total points
ID: 41783919
by default the subnet at the 3rd party is not known by the branch, hence the Fortigate 60D should add a static route to forward corresponding traffic to the HQ, otherwise the traffic to 172.1.1.0 subnet will be sent to the Internet by default.

therefore the following route need to be added at 60D:

From: 192.168.2.0/24
To: 172.1.1.0/24
Gateway: 192.168.1.1

nothing else need to be changed. just one more route to be added on the 60D at the branch.
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Author Comment

by:dsuy
ID: 41784724
Thanks, that's what I had done by creating a PBR, but it didn't work. I then created a Static Route and it started to work.
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Author Closing Comment

by:dsuy
ID: 41784726
Marking as solution
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