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Comment by snuxoll | Hacker News Reader

> if anything home ISP's need a slap on the wrist for their stingy DHCPv6 delegations of what basically amount to a SINGLE ipv6 address or some weird less-than /64. splitting a 56 is a better idea here.

This is the single most infuriating issue with IPv6 rollout in the US. CenturyLink is starting to roll out native IPv6 support (instead of 6rd which they've been using for years), the only issue is you get a single /64. I mean, I have no use for giving every single host a /64, but I've got five or six VLAN's and without at least a /56 I've got no way of actually deploying IPv6 on my network. By the way, this is a business DSL connection too - so it's not like they shouldn't expect something more than your typical flat home network where everything sits on a single broadcast domain.

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>I mean, I have no use for giving every single host a /64, but I've got five or six VLAN's and without at least a /56 I've got no way of actually deploying IPv6 on my network.

Why can't you subnet the /64? CenturyLink isn't doing dot1q tagging to you, so you must have a router with tagged interfaces on your network.

Edit: Imagine this is because you want to use SLAAC.

because if you want slaac to work without nat, the smalles ipv6 subnet you can have is a /64. so if your provider gives you just a single static /64, all you can allocate is a single subnet.

> Edit: Imagine this is because you want to use SLAAC.

Not just because of SLAAC, prefixes smaller than /64 are likely to mess with all sorts of assumptions built into networking gear. It may not be "correct" since there are valid reasons for subnets as small as a /127 (though they are used infrequently enough at least), but a lot of networking gear cheats with IPv6 routes to keep the amount of TCAM memory needed down. Why spend 128-bits per route and quadruple the memory required when you can double it and go 64-bits per route and dump the longer ones to slower DRAM (I mean, you only use /127's for point-to-point links that don't need link-rate switching anyway)?

Regardless of anyone's philosophy of address assignment strategies, prefixes smaller than /64's in IPv6 are un-wise unless you want to degrade into worst-case routing paths on your network gear.

Somewhat of a good point, but I don't think it applies here - some implementations, particularly inexpensive devices like SOC's, do exact search on common prefix lengths like /64 and /48. I can't imagine this would be a huge problem within a home network, though. Even then, DRAM, which is essentially software switching, is rarely used. Further, you said you had 6 VLANs - this is well within the route scale of the vast majority of network devices regardless of how they implement their lookup data structures.

Good example: The SRX300, a desktop router/firewall implemented on a MIPS based Cavium Octeon (both control and data plane) can handle up to 256K IPv6 routes: https://www.juniper.net/assets/us/en/local/pdf/datasheets/10...

The Trident series SOC's can do 8K by default, and 64K with ALPM enabled: https://www.juniper.net/us/en/local/pdf/datasheets/1000480-e...

>(I mean, you only use /127's for point-to-point links that don't need link-rate switching anyway)?

/126's and /127's are often used for PTP's for peering/transit. Line rate is table stakes. Bear in mind that the gear used in these situations has plentiful lookup memory (SRAM, RLDRAM, HMC, or HBM).

RFC4193 "Unique Local Addresses" may be your only hope when you need multiple VLANs and only a /64 allocation. You then use NPT. Basically, its a bit like RFC1918 + NAT. The horror ...

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