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0 pointssgjohnson2y ago0 comments

I kind of just winged it. But IPv6 is really super similar to IPv4. The key differences are:

- 128-bit addresses, expressed in hexadecimal. A single character is 4 bits (making every 4 bits a nibble boundary, making allocations really easy)

- All subnets are /64 (if you really want to have a different size subnet, you can, but it’s against the standard, and anything other than /64 will break SLAAC. There is one exception to the standard—point to point links are allowed to have a /127)

- The concept of a network address or a broadcast address within the subnet doesn’t exist. ff02::1 is the all-nodes link-local multicast address (serves the same purpose as a broadcast address in v4).

- ARP is gone. A very similar protocol, ND takes its place

- The preferred way to assign addresses to endpoint devices is SLAAC. Which is basically the router telling the endpoints to self-assign. Ridiculously small chance of a collision, and in case a collision happens, just run the rng again. It’s 64 bits after all. You can use DHCPv6 instead or in tandem with SLAAC if you need more granularity.

- You don’t need to use NAT. Which means you have to set up a firewall on the router correctly. Default-deny, while still allowing ALL ICMP traffic through, as ICMP is kinda vital for IPv6 because it’s used to communicate error conditions.

I’m sure I’ve missed something, but these are all the differences I can recall from the top of my head.

0 comments

jpdb2y ago

> You don’t need to use NAT. Which means you have to set up a firewall on the router correctly. Default-deny, while still allowing ALL ICMP traffic through, as ICMP is kinda vital for IPv6 because it’s used to communicate error conditions.

I do think using NAT in the form of NPTv6 is awesome for home use because it allows you to have a consistent address regardless of your ISP prefix assignment.

Think of NPTv6 as a kind of "stateless NAT" where the prefix is mapped 1:1 to your internal prefix. This means if your ISP changes your address, you only need to your external DNS versus all of your devices.

sgjohnsonOP2y ago

> This means if your ISP changes your address

Yes. If your prefix is dynamic, stateless NAT66 can reduce some headaches. But that’s just about the only use case.

teddyh2y ago

You don’t need a system for assigning IPv4LL addresses (169.254.0.0/16), since IPv6 has automatic link-local addresses on all interfaces.

cchance2y ago

Gotta say i had to check wtf a nibble was lol

blooalien2y ago

A nibble is half a byte. (4 bits) Arcane binary maths wizardry from way back when every single bit had value to the programmers, and 64 Kilobytes was a lot of RAM. ;)

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