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DHCPv6-PD – First Steps

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Re: DHCPv6-PD – First Steps

#41

Post by hairyplanter »

yjftsjthsd-h wrote: post #37
hairyplanter wrote: post #32

Earlier quoted context omitted.

ULA is still the right solution here. ULA would let you maintain your internal lan with custom subnets and DNS even if you switch carriers or use multiple carriers. No need to update your internal DNS servers for ULA. If you're running a server on your dynamic residential service, you must be using dyndns for ipv4. So do the same with ipv6. Residential random prefixes is the nature of residential networks, as ISPs do…

I guess I'll ask here... How do I learn this? I'm comfortable with IPv4, including DHCP, DNS, VPNs, NAT, whatever. I'd like to be able to set up a v6 network[0] in whatever is the Correct and sane way. Is there a good end-to-end tutorial to set it all up by hand and explain what all these things (RA/DHCPv6/fe80::/ULA/etc.) are and how to use them or why not to use them? [0] Ideally pure v6 if possible; I think there'…

I haven’t seen one. Openwrt seems to do the right thing out of the box, but that’s not that helpful in setting up your own and learning on the way.

Maybe I will write one this weekend and make a hn post.

Re: DHCPv6-PD – First Steps

#42

Post by pantalaimon »

hairyplanter wrote: post #31
zamadatix wrote: post #26

Earlier quoted context omitted.

For those with flatter home network needs but still wanting a few things internal to be reachable by IP I'll throw in you can also use static link locals on fe80:: instead of a random ULA prefix. You'll still need the ULA method if you have multiple subnets and want static services reachable via routing though. Unless the router says the old prefix now has a valid lifetime of 0 the proper thing to do is actually to w…

As browsers don't like link local addresses in the address bar, ULA is still better.

You always have to specify the interface that goes with them since they are only guaranteed to be unique on the link.

Re: DHCPv6-PD – First Steps

#43

Post by pantalaimon »

Tigress8780 wrote: post #16
j16sdiz wrote: post #7

Earlier quoted context omitted.

No. In IPv6, you can get an address using RA. DHCPv6 only if you want to smuggle some unrelated metadata as options (which, of course, not widely used outside enterprise). DHCPv6-PD are used only when you need a whole prefix. If everybody implement all the specs out there, we will have two different DNS record type, 4 or 5 address allocation schemes, a handful of IPv6-over-IPv4 protocol, whole a lots of incomplete an…

SLAAC is fine, until you somehow get a subnet smaller than /64 on your router, in which case SLAAC completely breaks. I understand why SLAAC has such a limitation, but this is what we get. It's not optimal, but the upstream network provider does not budge, and now everything except Android devices get IPv6 address via DHCPv6.

There was a proposal for variable length SLAAC, but it went nowhere

https://datatracker.ietf.org/doc/html/draft-mishra-6man-vari...

Re: DHCPv6-PD – First Steps

#44

Post by pantalaimon »

hamandcheese wrote: post #11
kiwijamo wrote: post #10

Earlier quoted context omitted.

Out of interest as I have found IPv6 RA to work flawlessly for my home network (alongside legacy IPv4 DHCP), what advantage (if any) is there in deploying DHCPv6 within the home LAN? Or were you meaning to say DHCPv6 is great for certain (enterprise?) use cases?

When I was experimenting with IPv6 on my lan, router advertisements indeed worked great! But the big loss was that I had no control to reserve a particular IPv6 address for a particular MAC address inside the DHCP server, or assign DNS names automatically, etc. since it's basically 1 way - device receives a RA then configures itself with a random address.

You could give the device a static address and let duplicate address detection do it’s thing

Re: DHCPv6-PD – First Steps

#46

Post by jodersky »

devman0 wrote: post #21
Tigress8780 wrote: post #16

Earlier quoted context omitted.

SLAAC is fine, until you somehow get a subnet smaller than /64 on your router, in which case SLAAC completely breaks. I understand why SLAAC has such a limitation, but this is what we get. It's not optimal, but the upstream network provider does not budge, and now everything except Android devices get IPv6 address via DHCPv6.

Unicast IPv6 addresses are required to have a 64 bit interface identifier and a 64 bit network identifier (e.g. /64), handing out subnets lower than /64 is not spec compliant. Network operators can do crazy things, but if you color outside the lines things may break.

AFAIK, it's not strictly true that unicast addresses are required to use a /64 network identifier.

It's common, almost necessary even, for environments with dynamic clients to use /64 subnets (precisely so that SLAAC works), but in a static environment it's perfectly fine to use prefixes larger than /64 (e.g. delegate a /80 to each individual host in a datacenter, for virtualization applications etc).

Hence, I'm wondering what the spec is you mention that is broken?

Re: DHCPv6-PD – First Steps

#47

Post by f_devd »

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.

Re: DHCPv6-PD – First Steps

#49

Post by dcow »

Uptrenda wrote: post #33

People who advocate for IPv6 are always like 'ahhhh just plug it in and its ready to go!!!' There's even twitter accounts that shame people for how they approach IPv6. But after doing a crap load of network programming I can tell you its really not simple at all. - IPv6 has many different address types. - Depending on the type you want to bind to it needs to be handled different. - Some types need an interface ID app…

scopes are deprecated and link-local is only a thing so that the network can bootstrap itself. if you’re deploying ipv6 all you care about are global and ula, which are scope-less

Re: DHCPv6-PD – First Steps

#50

Post by thwarted »

yjftsjthsd-h wrote: post #37
hairyplanter wrote: post #32

Earlier quoted context omitted.

ULA is still the right solution here. ULA would let you maintain your internal lan with custom subnets and DNS even if you switch carriers or use multiple carriers. No need to update your internal DNS servers for ULA. If you're running a server on your dynamic residential service, you must be using dyndns for ipv4. So do the same with ipv6. Residential random prefixes is the nature of residential networks, as ISPs do…

I guess I'll ask here... How do I learn this? I'm comfortable with IPv4, including DHCP, DNS, VPNs, NAT, whatever. I'd like to be able to set up a v6 network[0] in whatever is the Correct and sane way. Is there a good end-to-end tutorial to set it all up by hand and explain what all these things (RA/DHCPv6/fe80::/ULA/etc.) are and how to use them or why not to use them? [0] Ideally pure v6 if possible; I think there'…

Hurricane Electric has a pretty decent IPv6 self-study certification program.

https://ipv6.he.net/certification/

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