When multiple TE tunnels have the same cost, traffic can be load-balanced across them. Traffic
can also be load-balanced between the native IP path and TE tunnels if the cost of the routing is
the same. This situation has some restrictions, however; see the earlier section “Cost Calculation
of IGP Routes over TE Tunnels.†When you are load balancing over TE tunnels, the load balancing
can even be unequal cost load balancing. The load balancing of traffic is weighted proportionally
to the bandwidth requirement of the TE tunnels. If you have one tunnel with 80 MB and one with
20 MB of reserved bandwidth, the load-balancing ratio is 4:1, or the first tunnel should get four
times more traffic than the second tunnel. However, the load-balancing ratio is an approximation,
because Cisco Express Forwarding (CEF) has only 16 hash buckets. See Chapter 6, “Cisco
Express Forwarding,†for more on this.
When an LSR performs the load balancing over one or more IP paths and one or more TE tunnels,
it is always equal cost load balancing. This means that every path gets the same amount of traffic.
Multiple TE tunnels can be handy when the amount of bandwidth to be reserved between a pair
of routers is more than the bandwidth capacity of the links. You can then just create multiple TE
tunnels with each a piece of the required bandwidth.
