31.2.0.0.1 Asymmetric Routing

Asymmetric routing occurs when the path from node $n_1$ to node $n_2$ is different from the path from $n_2$ to $n_1$. The following shows a simple topology, and cost configuration that can achieve such a result:

Nodes $n_1$ and $n_2$ use different paths to reach each other. All other pairs of nodes use symmetric paths to reach each other.

    \$ns cost \$n1 \$r1 2
    \$ns cost \$n2 \$r2 2
    \$ns cost \$r1 \$n2 3

Any routing protocol that uses link costs as the metric can observe such asymmetric routing if the link costs are appropriately configured^31.3.