A customer has requested that the service provider use a Cisco MPLS TE tunnel to force the E- line service to take a specific route. What is used to send the traffic over the tunnel?

While a static route can direct traffic, it's not the primary or most scalable method for dynamic traffic steering over MPLS TE tunnels in a service provider network, which typically relies on IGP integration.

When an MPLS TE tunnel is configured as a 'preferred path,' it signals to the Interior Gateway Protocol (IGP) to favor this tunnel for specific prefixes or destinations. This causes the IGP to install a route via the TE tunnel, effectively steering the traffic for the E-line service over the engineered path.

A forwarding adjacency allows an MPLS TE tunnel to be advertised into the IGP as a link, effectively making the tunnel appear as an IGP adjacency. While this influences routing, 'preferred path' is a more direct mechanism to specifically prefer the tunnel for traffic.

Autoroute destination is a feature that allows a TE tunnel to be advertised into the IGP for all destinations reachable via the tunnel's endpoint. This makes the tunnel a viable path in the IGP's SPF calculation, but 'preferred path' specifically denotes preference over other equal-cost paths.