HNA problems

Figure: Node alters between having connection with Intermediate Node 1(IN1) and Intermediate Node 2(IN2) causing Internet traffic to alter between being routed through Gateway1(GW1) and Gateway2(GW2).

OLSR sets up hop-by-hop routes. This means that while calculating the complete route locally, olsrd will just enter the next hop on the path to the destination into the routing table. Therefore OLSR routing is depending on the distributed operation of the protocol since the sender has no control of where the next hop router routes the traffic. This also goes for HNA routes. If A has a static link to IN1 and no link to IN2 in the scenario depicted in figure 13.1, it will use GW1 as its Internet gateway. The route added to the kernel routing table will be:

Network: 0.0.0.0
Gateway: IN1
metric:  2

IN1 will have a route entry:

Network: 0.0.0.0
Gateway: GW1
Metric:  1

If A, for some reason, wishes to communicate through GW2, it simply cannot. A cannot add GW2 as the gateway since a gateway is to be the next hop along the path. Because of this a route to GW2 would be:

Network: 0.0.0.0
Gateway: IN1
Metric:  3

But when this traffic arrives at IN1, it will be routed via GW1. This fact causes problems in several ways.