HNA - route calculation

HNA routes are recalculated on all changes in the topology or the HNA set. If there exist multiple gateways to the same network, the gateway closest(in hop-count) is chosen.

HNA routing is done hop-by-hop. This means that HNA routes are added with the next-hop neighbor on the route to the gateway as the actual gateway to the HNA announced network. In a scenario like the one illustrated in figure 4.3, A would add the following entry to its routing table:

destination: 0.0.0.0/0
gateway: B
metric: 3

This means that the actual gateway who announced the external connectivity is not added to the routing table.

Figure: A would add B as its Internet gateway.