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0 points0x4571y ago0 comments

Wait, what's not standard about /64?

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4 comments · 2 top-level

hylaride1y ago· 2 in thread

Strictly speaking, it's perfectly standard and you can subdivide it (manually). However, for a variety of reasons subnetting smaller than a /64 is difficult and not supported at all via SLAAC (because the host portion is derived from the MAC which is already 48 bits, plus other overhead). So if you want to split up a /64 from your ISP, you're limited to manual configuration, DHCPv6 (and no android support), or other ways:

https://version6.ru/en/dividing-the-indivisible

If you're just dealing with a single network at home, a /64 is otherwise fine. But there's a reason the recommended handout from ISPs is a /56; the inventors of IPv6 (or more specifically SLAAC) just didn't take into consideration how intransigent big telecoms would be.

0x457OP1y ago

I understand that, but what I'm replying to says: "TBH ISPs that hand out /64's shouldn't be allowed to say that they support IPv6 because it's a completely non-standard — not as in "uncommon", but as in "violates the documented standards" - setup."

hylaride1y ago

RFC6177 specifically recommends a /48 to /56 because future security measures may require subnetting, even on home networks (eg having IoT devices on a secure DMZ).

Basically, giving out a /64 is the modern equivalent to ISPs saying "you have to pay extra to have more computers on the internet and you're not allowed to use NAT" that was actually a thing up until the mid 2000s.

The frustrating this is that there's no reason to do a /64 as IPv6 was literally designed to hand out huge IP ranges.

1 more reply

kstrauser1y ago

RFC 3177[0] says:

"In particular, we recommend:

- Home network subscribers, connecting through on-demand or always-on connections should receive a /48.

- Small and large enterprises should receive a /48.

- Very large subscribers could receive a /47 or slightly shorter prefix, or multiple /48's.

There was some walking that back in later RFCs, arguing that home customers could get by with just a /56.

[0] https://www.rfc-editor.org/rfc/rfc3177.txt

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