Fortigate routing issues over IPsec VPN

Posted on 2014-10-14
Last Modified: 2014-11-23

We have a Fortigate 310B, which is our firewall.
Firmware: 5.0.7

We have multiple IPsec VPN tunnels to different companies and from several branch offices etc.

After creating a new physical interface we are seeing that remote locations(branch offices etc.) which is connected to us attempts to use the new physical interface as the default gateway when routing over the IPsec VPN tunnel.

Created another new physical interface, and the issue is the same. The only difference is that remote users over IPsec now sees this interface as their gatway, when routing over the IPsec Tunnel.

Applies only to interface/Route based IPsec VPN tunnels.

The routing sill works from remote locations over IPsec VPN, however we have a a few VPN Concentrators which is critical to our branch offices to access other companies network. As long as a new physical interface is active with an IP-Address the concentrator stops working all together.

Examples where a user from remote location tries access a server at our Lan and a remote company over a concentrator.

Without the new physical interfaces, the routing is normal

With a new physcial interface

With new physical inteface and to remote company over ipsec
* * * timeout
* * * timeout

Our physical interfaces are as follow:
P1 Internet: Public IP
P9: (newly created)

Anyone experienced anything similar with a Fortigate or know what is causing this issue ?

Question by:Lenblock
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LVL 39

Expert Comment

by:Aaron Tomosky
ID: 40381342
No personal experience, but my google-fu has found references to the placement of the policy in the config having effects like this.

Author Comment

ID: 40381814

Tried that, without luck.

I've set the physical interface to deny ping (icmp), and created no policies for it.
The remote computer still uses the Physical interface as a gateway.
LVL 39

Expert Comment

by:Aaron Tomosky
ID: 40382579
Perhaps this will help?

Hopefully someone with more fortigate experience will show up.
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LVL 22

Expert Comment

by:Jakob Digranes
ID: 40383726
what routes are setup for the device?

Author Comment

ID: 40383934

Static routes for the following:

Default route to internet.
All IPsec VPN Interface Based Tunnels.
All Branch offices which is connected over our IPS's network


Author Comment

ID: 40386270

Possibly found the cause for this.

Each Interface on the Fortigate is given an index number.
When creating the new interface on port9 it was given an index number lower than port5.
Fortigate decides which interface should be used as the next hop based on the index number.

Therefore remote computers over an IPsec Interface would use port9 as their next hop.

Looking into how we would go about changing the index number for an interface.
Not yet found out how.

Anyone know how or can suggest a different solution ?


Accepted Solution

Lenblock earned 0 total points
ID: 40451735

For any others looking for the answer:
If you enable multiple networks on multiple ports on a fortigate without vdom it will use the port with the lowest index as the default next hop in routing. You cannot change the index number. This is a problem if you have a IPsec concentrator.

Enabling vdom and separating the additional network solves this issue.

Author Closing Comment

ID: 40460415
Enabling vdom solves it.

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