VTI - Virtual Tunnel Interface

Set Virtual Tunnel Interface

set interfaces vti vti0 address 192.168.2.249/30
set interfaces vti vti0 address 2001:db8:2::249/64

Results in:

vyos@vyos# show interfaces vti
vti vti0 {
    address 192.168.2.249/30
    address 2001:db8:2::249/64
    description "Description"
}

Warning

When using site-to-site IPsec with VTI interfaces, be sure to disable route autoinstall

set vpn ipsec options disable-route-autoinstall

More details about the IPsec and VTI issue and option disable-route-autoinstall https://blog.vyos.io/vyos-1-dot-2-0-development-news-in-july

The root cause of the problem is that for VTI tunnels to work, their traffic selectors have to be set to 0.0.0.0/0 for traffic to match the tunnel, even though actual routing decision is made according to netfilter marks. Unless route insertion is disabled entirely, StrongSWAN thus mistakenly inserts a default route through the VTI peer address, which makes all traffic routed to nowhere.