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DHCPv6-PD – First Steps

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Re: DHCPv6-PD – First Steps

#51

Post by greenicon »

f_devd wrote: post #47
ninkendo wrote: post #23

This article hints at what I consider to be the biggest technical drawback to IPv6 for residential use, which is that dynamic prefixes mean your internal LAN IPs are never stable. The answer to this is usually something like “duh, use DNS”, but how are you going to configure that DNS server if your whole network’s IP address range could change at any time? Yes, multicast DNS is a thing, but it’s not supported in all…

My only gripe with IPv6 is that clients use an entire /64, I get it's useful for SLAAC, but I wish I could make clients receive a /68 or more with DHCPv6 so that the address space can be subdivided even when you are already behind a /64 prefix.

That’s exactly what prefix delegation is for. Your ISP ought to give an /56 or more, so you can then have multiple /64.

I get an /56 by my ISP and have 6 or so different /64 in my residence.

Re: DHCPv6-PD – First Steps

#52

Post by derkades »

ninkendo wrote: post #23

This article hints at what I consider to be the biggest technical drawback to IPv6 for residential use, which is that dynamic prefixes mean your internal LAN IPs are never stable. The answer to this is usually something like “duh, use DNS”, but how are you going to configure that DNS server if your whole network’s IP address range could change at any time? Yes, multicast DNS is a thing, but it’s not supported in all…

Unfortunately, it seems that support for automatically configuring multiple addresses is quite poor. Linux it can be done with NetworkConfiguration or Netplan: use SLAAC to get a GUA and DHCPv6 for a ULA. NetworkManager also seems to use both by default. Android does not support DHCPv6 at all. I don't know about Windows, iOS, or macOS.

Re: DHCPv6-PD – First Steps

#53

Post by krylon »

hairyplanter wrote: post #30
ninkendo wrote: post #23

This article hints at what I consider to be the biggest technical drawback to IPv6 for residential use, which is that dynamic prefixes mean your internal LAN IPs are never stable. The answer to this is usually something like “duh, use DNS”, but how are you going to configure that DNS server if your whole network’s IP address range could change at any time? Yes, multicast DNS is a thing, but it’s not supported in all…

> or just bite the bullet and use ULA. This is the proper ipv6 solution. With ipv6, one ethernet interface is _supposed_ to have multiple addresses. You wouldn't want your lan routing to stop working when your ISP goes down, right? So configure your internal DNS with ULA (which should be stable for each machine for a given prefix, even with SLAAC) and be done with it, much like internal DNS using private addresses in…

I never heard of ULA before, and it sounded a bit overwhelming at first. But on a Fritz!Box with recent firmware, it's very easy to enable, and voila! - just works.

Re: DHCPv6-PD – First Steps

#54

Post by simoncion »

derkades wrote: post #52
ninkendo wrote: post #23

This article hints at what I consider to be the biggest technical drawback to IPv6 for residential use, which is that dynamic prefixes mean your internal LAN IPs are never stable. The answer to this is usually something like “duh, use DNS”, but how are you going to configure that DNS server if your whole network’s IP address range could change at any time? Yes, multicast DNS is a thing, but it’s not supported in all…

Unfortunately, it seems that support for automatically configuring multiple addresses is quite poor. Linux it can be done with NetworkConfiguration or Netplan: use SLAAC to get a GUA and DHCPv6 for a ULA. NetworkManager also seems to use both by default. Android does not support DHCPv6 at all. I don't know about Windows, iOS, or macOS.

> Unfortunately, it seems that support for automatically configuring multiple addresses is quite poor.

What? SLAAC configures addresses on all -er- not-expired prefixes advertised on the link. So, if the border router advertises a ULA prefix and a globally-routeable prefix, SLAAC assigns two addresses to the computer.

If whatever network-configuration tooling you're using causes your computer to not generate an address for every advertised prefix (and you've not told the tooling to behave in this way) then it's broken.

Re: DHCPv6-PD – First Steps

#55

Post by OJFord »

hairyplanter wrote: post #30
ninkendo wrote: post #23

This article hints at what I consider to be the biggest technical drawback to IPv6 for residential use, which is that dynamic prefixes mean your internal LAN IPs are never stable. The answer to this is usually something like “duh, use DNS”, but how are you going to configure that DNS server if your whole network’s IP address range could change at any time? Yes, multicast DNS is a thing, but it’s not supported in all…

> or just bite the bullet and use ULA. This is the proper ipv6 solution. With ipv6, one ethernet interface is _supposed_ to have multiple addresses. You wouldn't want your lan routing to stop working when your ISP goes down, right? So configure your internal DNS with ULA (which should be stable for each machine for a given prefix, even with SLAAC) and be done with it, much like internal DNS using private addresses in…

What's the point of using IPv6 at all on a home network if you use ULA though? If you continued to use an IPv4 setup you were familiar with but allowed your router to talk both or v6 only, wouldn't it be the same?

Is it that you'd still have the globally addressable addresses on NICs with a ULA too, just that's not what you'd use for routing internally? (Not that I'm really sure of the benefit of that residentially either?)

Re: DHCPv6-PD – First Steps

#56

Post by simoncion »

krylon wrote: post #53
hairyplanter wrote: post #30

Earlier quoted context omitted.

> or just bite the bullet and use ULA. This is the proper ipv6 solution. With ipv6, one ethernet interface is _supposed_ to have multiple addresses. You wouldn't want your lan routing to stop working when your ISP goes down, right? So configure your internal DNS with ULA (which should be stable for each machine for a given prefix, even with SLAAC) and be done with it, much like internal DNS using private addresses in…

I never heard of ULA before, and it sounded a bit overwhelming at first. But on a Fritz!Box with recent firmware, it's very easy to enable, and voila! - just works.

Yep! ULA should be thought of as the IPv6 equivalent of RFC 1918 space... with the added bonus that -unlike with IPv4- ULA prefixes are very unlikely to collide, so merging internal networks will very rarely require renumbering.

Re: DHCPv6-PD – First Steps

#57

Post by simoncion »

candiddevmike wrote: post #2

While the article is focused on OpenBSD, implementing DHCPv6 with systemd-networkd is really slick and typically a 1-2 line config for your interfaces: Upstream: [DHCPv6] PrefixDelegationHint=::/56 Downstream: [DHCPv6PrefixDelegation] Token=::1

While I understand that this would not be a situation that's typical for a residential LAN, how does systemd-networkd handle assigning prefixes assigned from multiple DHCPv6-PD assignments?

To make it more concrete, imagine for a moment that one's border router has multiple WAN interfaces, each with its own prefix delegated to it.

I notice that there's an UplinkInterface parameter [0], but if the documentation is not silent on whether or not there's any support at all for delegating multiple prefixes to the same LAN interface, then I missed it.

[0] https://man.archlinux.org/man/systemd.network.5#%5BDHCPPREFI...>

Re: DHCPv6-PD – First Steps

#58

Post by simoncion »

kccqzy wrote: post #29
ninkendo wrote: post #23

This article hints at what I consider to be the biggest technical drawback to IPv6 for residential use, which is that dynamic prefixes mean your internal LAN IPs are never stable. The answer to this is usually something like “duh, use DNS”, but how are you going to configure that DNS server if your whole network’s IP address range could change at any time? Yes, multicast DNS is a thing, but it’s not supported in all…

Your rant doesn't make sense. The solution is already known and you mention it: ULA. It's not a compromise. You don't need to bite the bullet. Just use it. It's designed for this use case. Fixed IP address for every single device.

Homie likes to pretend to overcomplicate things. Check the comment history, this rant isn't new.

And yeah, folks need to understand that ULA addresses are functionally equivalent to RFC 1918 addresses, and ask themselves why they'd expect an ISP who charges extra for an unchanging globally-routable IPv4 address to give you an unchanging globally-routable IPv6 prefix for free.

Re: DHCPv6-PD – First Steps

#59

Post by simoncion »

ninkendo wrote: post #23

This article hints at what I consider to be the biggest technical drawback to IPv6 for residential use, which is that dynamic prefixes mean your internal LAN IPs are never stable. The answer to this is usually something like “duh, use DNS”, but how are you going to configure that DNS server if your whole network’s IP address range could change at any time? Yes, multicast DNS is a thing, but it’s not supported in all…

> ...they don’t drop the old one until the lifetime expires...

That's a configuration problem on your end. Your border router needs to notice that it's being instructed to switch delegated prefixes and instruct radvd (or whatever route advertising daemon it's using) to advertise the now-defunct prefixes with a zero lifetime just before or just as you're advertising the new prefixes.

With this information, devices on your LAN that aren't asleep will do the right thing, and devices that were asleep should reconfigure their network interfaces when they wake up... assuming that the world hasn't changed while they've been asleep is something only morons would do (coughAppleComputerscough).

Re: DHCPv6-PD – First Steps

#60

Post by simoncion »

greenicon wrote: post #51
f_devd wrote: post #47

Earlier quoted context omitted.

My only gripe with IPv6 is that clients use an entire /64, I get it's useful for SLAAC, but I wish I could make clients receive a /68 or more with DHCPv6 so that the address space can be subdivided even when you are already behind a /64 prefix.

That’s exactly what prefix delegation is for. Your ISP ought to give an /56 or more, so you can then have multiple /64. I get an /56 by my ISP and have 6 or so different /64 in my residence.

Sadly, I've only ever gotten /60s. 16 subnets is better than zero, but it's far less than 256.
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