Jou (Mxyzptlk)Silver badge
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Re: The real reason nobody wants to use it
Not sure why they thought that would be a good idea.
Actual I think multiple addresses is a good idea.
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The FE80::/7 is the former 169.254, always active, used for "same link" things, to some extend it replaces ARP, prevents ARP storms by design. Has the MAC coded into the address.
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The FEC0::/10 (usually subnetted in /64 packets), similar to 192.168.x.x, but no "default gateway" for Internet desired, only clear other LAN destination routes.
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The FC00::/7 (usually subnetted in /64 packets), similar to 10.x.x.x, but no "default gateway" for Internet desired, only clear other LAN destination routes.
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The FD00::/8 DO NOT USE (usually subnetted in /64 packets), similar to 172.16.x.x, but no "default gateway" for Internet desired, only clear other LAN destination routes. This got removed from the standard somewhere in the last 20 years and replaced by FC00::/7 which included FD00::/8, therefore better avoid.
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The FF00::/8 is multicast, similar to the 224.x.x.x
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Finally the actual internet address, usually 2001:whateverfirst64bits:your-pseudo-static-part. Depending on the provider your prefix might be /56 /48 as well. The yourpseudosstaticpart is, on many devices, optionally with privacy extensions, so they are random and change over time even if your provider does not force-disconnect-reconnect. How much "privacy" that offers is a discussion for another decade.
Normal homes have 1 and 6. Über-Nerd homes or companies with somewhat clean ipv6 adaption have 1, 2 or 3 (not both please!), and 6 to organize their WAN/LANs. Enlightened Nerds include 5 too.
2 and 3 have the advantage that they are DEFINETLY not to be used for internet, no gateway to the internet, and therefore safe for LAN. I am nerd, but don't give a s, so I have 1 and 6, and my fd address is there for historic reasons since I played with ipv6 over a decade ago but not active in use.
My gripe is a lot of the things around it which makes ipv6 a hassle, especially when your prefix from 6 changes, all you adapters, and I mean ALL ACROSS YOUR WHOLE LAN, have to automatically follow suit. Which means: When connected to the Internet a lot of formerly static ipv4 configuration cannot be static any more - unless your provider gives you a fixed ipv6.
KurganSilver badge
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Re: The real reason nobody wants to use it
My gripe is a lot of the things around it which makes ipv6 a hassle, especially when your prefix from 6 changes, all you adapters, and I mean ALL ACROSS YOUR WHOLE LAN, have to automatically follow suit. Which means: When connected to the Internet a lot of formerly static ipv4 configuration cannot be static any more - unless your provider gives you a fixed ipv6.
This is one of the worst parts of it. And even if your provider gives you a static assignment, what happens when you change provider? Or if you failover on a multi wan connection? Or even try to load balance on a multi wan connection?
The only way IPV6 can be used with the same (even better) flexibility of v4 is when you own you v6 addresses and use a dynamic routing protocol, which is not what a small business usually does. A home user even less.
Then there is the security nightmares v6 can give you. I can't even imagine how many ways of abusing it are simply yet to be discovered, apart from the obvious ones like the fact that even if you don't use v6 to connect to the internet, you LAN has FE80 addresses all around and you have to firewall the hell out of it unless you want someone that penetrated the LAN to use them to move laterally almost for free.
12 hrs
Nanashi
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Re: The real reason nobody wants to use it
fec0::/10 is long deprecated, and it's a bit odd to tell us to avoid fd00::/8 in favor of fc00::/7 when the latter includes the former. fc00::/8 is intended for /48s assigned by some central entity (but none has been set up, since there doesn't seem to be a pressing need for one) and fd00::/8 is for people to select their own random /48s from, so if you want to use ULA then you'll be picking a /48 from fd00::/8.
It's not exactly hard to hand out a new prefix to everything. Your router advertises the new subnet, and every machine across your whole LAN receives it and automatically configures a new IP from it.
Anything that assumes your IPs are never going to change is already broken. Maybe we should focus a teeny bit of the energy we spend complaining about it into fixing the brokenness?
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Most of your first questions can be broadly answered by a mix of "you advertise a /64 from the prefix that the provider gives you" and "you can use multiple addresses". And it doesn't sound like your use of v4 is very flexible if it can't handle your IPs changing sometimes.
