How does routing behave with BOVPN Virtual Interfaces if VPN routes are defined and the virtual interface IP adresses is activated? How do the virtual interface IP addresses behave?
If routes are activated for the BOVPN VIF, they will be followed, unless another route supersedes it. The benefit of multiple routes will generally only come into play when using dynamic routing, but could be useful in other scenarios.
Generally, the choice as to if you're going to use a VIF or a standard VPN will come down to what's set up on the distant end -- you'll need to match that.
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are there any disadvantages of virtual interface configuration compared to standard VPN ?
Not all remote devices can support this type of BOVPN.
About BOVPN Virtual Interfaceshttps://www.watchguard.com/help/docs/help-center/en-US/Content/en-US/Fireware/bovpn/manual/bovpn_vif_about_c.html