<WG Chair Hat Off> Hi!
On 10/10/13 5:07 PM, "Alia Atlas" <[email protected]<mailto:[email protected]>> wrote: . . . 1. * Root Selection. No algorithm is provided. There's a reference to I-D.atlas-ospf-mrt, where a suggestion is made ("..the router with the highest GADAG Root Selection Priority is picked to be the GADAG Root"). IMHO, the algorithm should be specified in this draft, where the requirement to carry the Priority is defined so that the extensions draft(s) can show how to implement it in OSPF (or any other protocol)..not the other way around. [Alia] The Root Selection is described in draft-ietf-rtgwg-mrt-frr-architecture in Sec 7 as '"GADAG Root Selection Priority: Among the routers in the MRT Island and with the highest priority advertised, an implementation MUST pick the router with the highest Router ID to be the GADAG root." This goes back to my comment above about the capabilities and the default profile definition: If this is part of the algorithm it should be specified in the algorithm draft, not somewhere else. [Alia] Ah - the GADAG root selection is part of the MRT profile but not, IMHO, part of the algorithm... The same Lowpoint algorithm can be used with different GADAG root selection. For example, for multicast, one might do an MRT profile where the multicast S is picked to be the GADAG root - and the same Lowpoint algorithm is run. But the performance of the algorithm can be affected by the selection of the root. In 6.1 you wrote: "The particular choice of a common GADAG root is expected to affect the quality of the MRT alternate paths, with a more central common GADAG root resulting in shorter MRT alternate path lengths." For the results you chose a centrally located node to be the root. What would have happened if the root had been selected randomly? (Or the equivalent which would be to assign random Priorities.) I guess my point here is that one of the reasons the Lowpoint algorithm performs well is because of how the root is selected. We could go back and forth all day about whether the root selection should be part of the "default algorithm" or just part of the "default profile"..but I think it would be more important to stress (even mandate) that the location of the nodes be considered when assigning the Priority. Note that the current text ("Off-line analysis that considers the centrality of a router may help determine how good a choice a particular router is for the role of GADAG root." -- which is too soft for my taste) is in the algorithm draft, not in the architecture draft (which defines the profile), so it may not be completely clear.. Thanks! Alvaro.
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