Description
This article describes specificity when changing Internet Service Providers.
Scope
FortiGate.
Solution
When changing ISP's follow the steps listed below :
- Change the external IP on the interface (System -> Network -> Edit Interface). Network -> Interfaces -> Edit.
- Delete old static routes (Router -> Static). Network -> Static Routes -> Delete.
- Create new static routes (Router -> Static). Network -> Static Routes -> Create New.
If updating an existing static route entry, make sure to update the gateway IP. Go to `Network -> Static routes`. Edit the default route 0.0.0.0 entry and provide the new gateway IP address on the static route.
To edit the static route from CLI :
config router static
edit <ID number>
set gateway x.x.x.x <----- New ISP provider gateway IP.
set distance 10
set device "port1"
next
end
A warning may appear if the gateway IP from the previous Internet Service Provider is not updated to match the new provider’s IP gateway.
In the screenshot below, the warning shows that the Gateway IP 100.92.16.100 is not reachable via the New Service Provider IP range 10.9.11.3/20.
- If the interface is a member of an SD-WAN zone, update the gateway address under the SD-WAN member as described in Technical Tip: How to modify WAN IP settings when using SD-WAN
- Kill all active sessions on the device. From the GUI:
diagnose sys session filter sintf <WAN>
diagnose sys session clear
diagnose sys session filter dintf <WAN>
diagnose sys session clear
- Change the external IP addresses on the VIP if there are any.
- If necessary, reconfigure the DNS servers on the device (System> Network> Options). Network -> DNS.
- Sometimes, after changing the service provider (ISP) the ARP entry is not registered as expected on FortiGate. Make sure to verify the ARP entry for the gateway:
get system arp
If the ARP is not registered, try to ping the gateway IP of the service provider to verify connectivity and the MAC address ARP entry:
execute ping-option source x.x.x.x [WAN ip address]
execute ping x.x.x.x [ISP gateway IP]
Note:
When defining the new Static Route, leave the Destination IP and Mask as 0.0.0.0, select the external interface for the unit, define the Gateway received from the Internet Service Provider, and leave the Distance set to 10.
To clear all active sessions, type: 'diagnose sys session clear'.
Related document:
