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[AfriNIC-rpd] Draft Policy: Anycast Assignments in the AfriNIC region

Bill Woodcock woody at
Wed Apr 18 16:45:18 UTC 2012

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On Apr 18, 2012, at 3:50 AM, McTim wrote:
> Well, typically Anycast uses one address, but routes the entire /24.  If an Anycast service provider got a /22 and only used 4 addresses, that would mean 1020 go unused, but all /24's are routed. It's more wasteful than letting them "waste" 254 IPs.


To expand a little on Tim's explanation, when you're advertising anycast services, you typically want to be able to advertise each one independent of the others, to the degree possible.  That is, if you're advertising Google's web site and Kenya's ccTLD, both are anycast, but if there's a problem with one, and you need to withdraw an instance of it from the routing table in order to keep queries from going unanswered, you don't want to also withdraw the other (completely unrelated) service, just because they happen to be in the same block of space.  Thus, you advertise each service from an address that's in a block with nothing else used.

Note that this doesn't indicate an inefficiency in the servers-per-address ratio…  It's quite possible that there are 256 servers utilizing that one IP address, out of a /24.  Because it's anycast, they're all using the same address, rather than all using different addresses, but the ratio of servers to addresses may well be identical, or possibly even better than one-to-one.  I'm not advancing that as an excuse for leaving 254 addresses fallow, however, just pointing out that it's not necessarily any worse than what people do with non-anycast addresses.

The real problem here lies not with anycast providers, nor with the RIRs, but with ISPs that indiscriminately block prefixes longer than /24, because they once heard, a long time ago, from someone older than themselves, that that was a good idea.  One rule I learned long ago is that if I'm going to learn something new about the Internet, it'll be from someone younger than me, not from someone older than me.  Blocking prefixes longer than /24 is a lazy inefficiency that will be worked out of the system by smart young people who are paying attention and want to use all 256 addresses in each /24, not just one of them.  But we're not quite there yet.

The part AfriNIC can do is consider minimum allocations longer than /24.  Not so much because they're needed yet, as because it would be a wake-up call to ISPs.


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