Wt routing protocol is best if an enterprise uses vpn to connect its branches through a single isp?

an enterprise uses vpn to connect its branches through a single isp and i want to know weather i should use IGP or EGP at the enterprise gateway to t

an enterprise uses vpn to connect its branches through a single isp and i want to know weather i should use IGP or EGP at the enterprise gateway to the isp.

or:an enterprise uses vpn to connect its branches through a single isp and i want to know weather i should use IGP or EGP at the enterprise gateway to the isp.

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