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Comment by tptacek | Hacker News Reader

Right but that's still not really answering his question. Sure, the constant factor is higher for router TCAM memory. Still: you can sum this post up as "in the late 1990s, tier-1 carriers filtered advertisements for all but the 'swamp' range down to /19s or smaller prefixes; now everything is the 'swamp'". Why is that?

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Because IPv4 address scarcity means small blocks get sold as they are available to people in completely different parts of the Internet. With IPv6 the address space is so large that they can easily keep the blocks in one piece.

No, obviously, I get that (we buy a lot of IPv4 space --- and I'm actually happier with the current regime than I was with the "supplicate to ARIN" regime). I'm just wondering what technologically happened to make universal /24 advertisements fine. I assume it's just that routers got better.

The transition to 7200 VXRs as core routers really hit a tipping point around 2000. They could handle millions of entries in the FiBs and really led to a relief in pressure. Subsequent devices had to match that.

On the IPv6 side; by 2002, nobody was really experimenting with A6 records any more, and EUI64 was needless. Both were parts of IPv6 designed to facilitate "easy" renumbering, so that single prefixes could be replaced with larger ones. But the ISPs weren't complaining any more about table size.

It's interesting to consider that the IPv4 address space is only 32 bits wide. Back in the early 2000s asking for 4GB of RAM was unthinkable, but today (well last year) that's not even a big ask. If your routing decision can fit in a single byte (which interface to use next) you could load the entire thing as a 4GB table easily. 8GB if you need two bytes for the next hop. Multicast might be a problem but since multicast doesn't work on the backbone anyway I think we can ignore it.

> I'm just wondering what technologically happened to make universal /24 advertisements fine. I assume it's just that routers got better.

Routers had to get better (more tcam capacity) because there wasn't much choice. Nobody wants to run two border routers each with the table for half the /8s or something terrible like that. And you really can't aggregate /24 announcements when consecutive addresses are unrelated.

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