Routing traffic through fortigate appliance from other subnets than the one the appliance is in.

Simon Blomsterlund 0

Hi!

I need to route traffic from a VNet to an on premise network through a fortigate virtual appliance. Since I'll need to use container environments I can't place the fortigate appliance in the same subnet as the container environment, since its subnet needs to be delegated to mcrsft.Apps/Environments.

I don't have access to edit the fortigate appliance's configuration. And I'm trying to debug this using a VM.

I have tried setting up a route table associated with the subnet connected to the VM. I have double checked that the network interface on the fortigate appliance is set to "allow IP forwarding".

I'm at the end of my wits and can not understand what I'm doing wrong.

I have disabled all NSG features during testing.

Fortigate appliance has the IP 172.16.2.10

The IP addresses I'm trying to access through the fortigate appliance are 195.80.240.0/20.

Subnet	CIDR
Subnet A (contains fortigate appliance)	172.16.2.0/24
Subnet B (contains my test VM)	172.16.3.0/24

I have set up the UDR

CIDR	Next hop	Associated subnet
195.80.240.0/20	172.16.2.10	SubnetB

But I can't ping anything in the 195.80.240.0/20 network. And I can't ping the fortigate interface IP from the test VM in the other subnet. If I place my test VM in the SubnetA I can access the target network.

KapilAnanth-MSFT 47,201 Reputation points Microsoft Employee

2024-07-10T10:13:18.5066667+00:00
@Simon Blomsterlund ,

Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.

Point to Note wrt "Since I'll need to use container environments I can't place the fortigate appliance in the same subnet as the container environment, since its subnet needs to be delegated to mcrsft.Apps/Environments."

Despite whether or not a subnet has delegation, it is always a good idea to deploy the NVA in it's own subnet

This is because, the NVA subnet should not have a UDR on itself and if you were to place a testVM and the NVA in same subnet, you will not be able to add a UDR to the testVM without affecting the NVA's routing.

Looking at your verbatim,

You can check the effective routes of a VM : Check NIC Effective routes

Can you check for TestVM and confirm the nextHop of 195.80.240.0/20 is the NVA's IP.

Can you confirm if the network range "195.80.240.0/20" is in Azure (VNET Peering or same VNET) or connected to Azure via VPN/ExpressRoute?

From the NVA, are you able to ping/telnet to "195.80.240.0/20" ?

If the NIC Effective routes indicate the packets are indeed being routed to the NVA, your next steps would be to

Check the NVA's configuration

Make sure the packet actually reached the NVA or not by checking the NVA's logs

Because, it is highly possible that the NVA is simply dropping the packets destined to "195.80.240.0/20"

Cheers,

Kapil
Simon Blomsterlund 0 Reputation points

2024-07-10T12:17:04.6766667+00:00
Thanks Kapil!

Yeah I checked the effective routes, and it seems to direct requests correctly to the NVA. Next hop for requests towards target network from VM in subnetB is the fortigate.

I have reached out to the service partner to check the NVA configuration. I'll try to update this thread if that is the case if someone else are trying to solve similar issues.

Cheers,

Simon
KapilAnanth-MSFT 47,201 Reputation points Microsoft Employee

2024-07-11T08:42:06.3933333+00:00

@Simon Blomsterlund ,

Sure.

Let us know if the packets actually reached the NVA and if so, did NVA drop the packet or forwarded to the destination "195.80.240.0/20".

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