North American Network Operators Group|
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Re: /24s run amuck
Sprint and a few others used to filter on /19s, 'cause that's what ARIN & others handed out. They changed that to /20s when the rules changed. Sprint gave that up.The filtering was done on the /18 because that was what I expected we could easily afford to support in terms of memory and computation, in terms of maximum number of prefixes.
The move to /19s was driven by two arguments: firstly, the regional internet registries explained how they would not allocate out half the available /19s within a generation of routing equipment, and secondly, it squelched many of the usual sources of complaint.
The deployment of progressive flap-damping further relieved the need to filter on short prefixes, and the subsequent complementary deployment of progressive maximum prefix count limits have essentially eliminated the need to do prefix-length filtering at all. Long prefixes now are simply less reliable than the covering shorter prefixes allocated by the RIRs. Just how unreliable a given prefix is would be difficult to predict, which is a misfeature, but the routing system as a whole is much more robust than it was a decade ago.
Unfortunately there has been a macroeconomic cost to the growth of background noise in the Internet -- and the noise is still there -- which has made the Internet as a whole more expensive and less widely available than it ought to be. However, there are much larger contributions of such waste outside the public Internet's routing system that dwarf the cost of the unnecessary demands on router power resulting from poor aggregation, poor hygiene, and poor stabilization practices.
Almost everyone filters on /24s - they do not want to see /32s in the global table.Why not? I'm curious about why /24s are OK but /32s are not.
I suggest that if there is no reason other than a watered down version of the voodoo mentality you've accused me personally of having with respect to long prefixes -- i.e., if you think I'm right about the problem but too aggressive about the limit -- that there is a business opportunity still waiting to be exploited by someone enterprising.
With respect to that, for my part I wish I could go back in time and complete the next phase of the filtering, viz. a web page which would accept a credit card number from anyone who wanted to have a particular prefix allowed through the access-list, for a small recurring fee.
Live and learn...