Alexandru Petrescu wrote: >Zach Shelby wrote: >> The issues is that some scalar metric representing the cost to the >> best ER through a Router should be advertised in RAs. What goes in >> the metric is determined by some routing algorithm but should be an >> easily comparable scalar for nodes to use simply to determine which >> router to use as a default without knowing anything about routing.
>Let me ask clarification about 'best router', in this example topology: > > ------ RA1 ------- RA3 ------- > |Host |---+--|Router1|-----|Router3|\ > ------ | ------- ------- \_______Internet > | ------- / > +--|Router2|--------------/ > RA2 ------- > >-what do you assume Host should choose as 'best router' - Router1, > Router2 or Router3? >-did I assume correctly the subnet structure above? In the figure above, I assume that "Internet" would represent the edge router and that the lines are the possible links, so the host can communicate directly with Router1 and Router2, but cannot reach router3 directly. The question is then if router1 or router2 should be selected. In my mind, the simplest model would be to represent the cost as hop count and in this case router1 would advertise the cost 2, while router2 would advertise the cost 1. The host would then select router2 based on lowest cost, which would in this case be the shortest route to edge router. In practical cases, this would be infinitely better than selecting routers by random, but still not perfect. A better model would be to take link quality into account. In this case, the cost going through router1 is a function of the link quality of the link to router1 and the cost from router1 to the edge router. It would probably be best to define the cost as the sum of the cost to router1 and the cost from router1 to the edge router and we should require the link cost to be at least one. By this procedure, it would still be possible to use just hop count, but also possible to use something slightly more sophisticated. Peter _______________________________________________ 6lowpan mailing list [email protected] https://www.ietf.org/mailman/listinfo/6lowpan
