Why do Cisco MPLS TE tunnels require a link-state routing protocol?
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MPLS Traffic Engineering (MPLS TE) tunnels are used to create explicit paths through the network, which allows service providers to control the flow of traffic in their network. MPLS TE tunnels are typically set up between specific routers and can be used to reserve bandwidth, ensure specific Quality of Service (QoS) levels, and improve network resiliency.
MPLS TE tunnels require a link-state routing protocol such as OSPF or IS-IS for several reasons:
Path Calculation: MPLS TE tunnels rely on the underlying routing protocol to calculate the best path between the tunnel endpoints. Link-state routing protocols, such as OSPF and IS-IS, use Shortest Path First (SPF) calculations to determine the best path through the network. By leveraging the SPF calculation, MPLS TE tunnels can be set up along a specific path, rather than relying on the default path chosen by the routing protocol.
Topology Discovery: Link-state routing protocols provide a complete view of the network topology. This information can be used by MPLS TE tunnel endpoints to select the best path for a tunnel. By analyzing the complete topology, MPLS TE tunnel endpoints can identify the most efficient path and ensure that the tunnel is set up along that path.
Bandwidth Reservation: MPLS TE tunnels can be used to reserve bandwidth along a specific path. Link-state routing protocols provide information about the available bandwidth on each link in the network. By using this information, MPLS TE tunnel endpoints can select a path with sufficient available bandwidth to meet the requirements of the tunnel.
Fast Reroute: MPLS TE tunnels can be used to improve network resiliency by providing a backup path in the event of a link or node failure. Link-state routing protocols provide information about the alternate paths available in the network. By using this information, MPLS TE tunnel endpoints can quickly reroute traffic onto a backup path in the event of a failure.
In summary, MPLS TE tunnels require a link-state routing protocol because they rely on the underlying routing protocol to calculate the best path through the network, provide a complete view of the network topology, allow for bandwidth reservation, and improve network resiliency through fast reroute.