Hi, Can anyone please tell me the answer to the following question? 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. Harsha.
-----Original Message----- From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu] On Behalf Of Harsha Narayan Sent: Monday, November 11, 2002 9:40 PM To: nanog@merit.edu Subject:
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.
Single-homed customers migrating to multi-homed is one thing that would cause this. --Phil
--On 11 November 2002 18:40 -0800 Harsha Narayan <hnarayan@cs.ucsd.edu> 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
Fundamentally, you can implement an allocation/assignment policy that optimizes utilization at the cost of aggregation or a policy that optimizes aggregation at the cost of utilization. The challenge is to find a reasonable solution in the middle of those extremes. -ron
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 <hnarayan@cs.ucsd.edu> 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
Generally ISPs use their own, in-house solutions for IP address assignment, although freeipdb and northstar are now available as well. Most ISPs don't assign address space with on-net aggregation in mind. Most aggregation occurs at the AS boundary. I can't say that I have ever found an ISP that emulated RIR practices, because addressing behavior is so different... - Most folks who receive space from their upstreams don't ever require more, and if they do, contiguous space is certainly not a requirement. - ISPs who receive space from RIRs will typically be back for more, at some point, and may turn in some space to get other, more aggregatable space. This requires some degree of forethought on the part of the RIRs who anticipate that someone receiving a /20 may be back for the second half of that /19 at some point. - Dan On Tue, 12 Nov 2002, Harsha Narayan wrote:
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 <hnarayan@cs.ucsd.edu> 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
participants (5)
-
Alex Bligh -
Daniel Golding -
Harsha Narayan -
Phil Rosenthal -
Ron da Silva