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Hi, This assignment algorithm is similar to the allocation algorithm used by the RIRs themselves to make allocations to ISPs (they call it "binary-bhop"). Are ISPs as aggregation-conscious as RIRs? Do ISPs use a commercial package to make assignments or do they write their own program or do they do it manually? I find that the allocations made by the RIRs are close to each other i.e. they are scattered over a lesser area. However, the assignments made by the LIRs are scattered over a wide area - it seems more random. Harsha. On Tue, 12 Nov 2002, Alex Bligh wrote: > > > --On 11 November 2002 18:40 -0800 Harsha Narayan <[email protected]> > wrote: > > > How do ISPs manage the allocations they get from the RIRs? More > > specifically, do they make the assignments from this sequentially or not? > > Are multihoming assignments to customers amidst non-multihoming > > assignments? > > > > I ask this because /23s and /24s seem to be scattered over a wide area > > - they are not adjacent to each other. > > Some ISPs use allocation strategies (within the block from the RIR) to > maximize the likelihood of a future request from the same customer being > capable of adjacent assignment in such a manner as to produce aggregatable > blocks, to reduce routing entries. The simplest dumb strategy if all > requests were of equal size would (effectively) be to reverse the binary > bits (for instance when allocating /24s out of a /16 allocate 0.0, 128.0, > 64.0, 192.0, 32.0, 160.0, 96.0, 224.0 and so on). Others use more informal > strategies (e.g.'well you may well want 2 x /24 but you are only entitled > to one x /24 on the basis of the current network plan. We'll give you one > now use the adjacent /24 last but if we have to use it in order to get > another block from the RIR then tough'). > > Generally there's only one block (or at most 2) active at a time in > most ISPs as the RIR won't issue another until utilization in existing > ones is good. However, there is of course reuse of space when customers > leave which also distributes address space. > > Alex Bligh >
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