[Kea-users] yet another question about multiple subnets %)

[Simon]

3 <babut at yandex.ru> wrote:

> what i told you about it. in general, prefixes are not important, the dhcp server operates with pools. you can generally specify the prefix "::/0" and forget about prefixes.

OK, so you have now demonstrated that you really don’t understand all this - and I strongly recommend you try some user-focussed material to learn. See below ...

> 
>> And in the IPv4 world it is possible for a client to ask for multiple addresses - it just needs to make multiple requests using a different client-ID for each one, and the server will handle them individually.
> in the world of dhcpv6, this cannot be done, since the rfc directly requires that one client has one identifier(windows follows this requirement strictly).
> ps: i see that you don't know ipv6 very well either ;)

For a client that wishes to be a single client and get a single IPv4 address, then that is correct. However, it is (depending on client capabilities) possible to effectively run multiple client instances, each with a unique ID - and then each instance will get a single address from the server. This is not at odds with the RFC you quote, is nothing to do with IPv6, and does not create an excuse to be abusive.


>> I have a feeling that you do not understand IPv6 too well, that’s understandable as some aspects are quite different to IPv4 - IPv6 is not just IPv4 with more address bits.
>> Two resources that come to mind are :
>> https://ipv6.he.net/certification/
>> You don’t need to go all the way through and get certified - just working through the stages which introduces concepts at a controlled rate making it easy to learn about them will help. When I wore it to my local LUG, the tee short was described as the "geekiest tee shirt ever” :D
>> https://github.com/becarpenter/book6/blob/main/Contents.md
>> While this is incomplete and there are whole chapters still to be written, there is some stuff in there which you should find helpful. It’s written by people who really do know IPv6 and have mostly been involved in it’s design over the years.
> actually, to understand something just read the source documentation, but the rfc for dhcpv6 is not easy reading :\ but there is no alternative to this. so refer to the places in the rfc(give quotes), and not someone's free narrative. you've never done that ;)

If you try learning how to USE IPv6 by reading the RFCs, then you will “find it very difficult”. That is why I have referred you to two resources I know of (there are others) which distill it down into a form the end user/network admin can follow reasonably easily.



3 <babut at yandex.ru> wrote:

> ps: and now a few words about life. who came up with this? who came up with the concept in which a client who has just hatched from an egg should request something from a world about which he knows nothing?! what is the name of the person responsible for this? the world should know its heroes! i will tell everyone who is responsible for the collapse of human civilization! this reptilian who flew to us with a mission to destroy humanity should be dismissed immediately!

No one said IPv6 was perfect - but it is a step forward from IPv4. There is no one person, but a lot of people who have put a lot of effort into genuinely trying to solve real world problems faced by real people running real networks.
One such problem in the IPv4 world is the assumption in so many aspects of networking that a host will have one IP address on an interface, assigned from a single subnet on that interface (we both know that both of these are incorrect, but while you can manually configure for it, you generally find a number of issues if you do). We now have the explicit requirement (not suggestion, absolute requirement) that hosts support multiple IPv6 addresses, from multiple prefixes, on an interface. This solves a real problem for many people - but as it stands today, the process for configuring this is imperfect.
There are aspects of IPv6 that I don’t particularly like, but I can see the benefits - and why some decisions were taken the way they are.

But ranting about the people who put a lot of effort into designing this is not the way to solve your problem. Personally, I’m not interested in helping someone who is not interested in helping him/her self, who refuses to accept that some of their assumptions/beliefs are incorrect, and throws insults around at anyone and everyone instead of trying to learn from what they are being told.


To summarise :
To achieve what you want, your router(s) must advertise the correct prefixes with the M flag set for clients to use DHCPv6 - if a client is using DHCPv6 without that then there is an issue.
The RAs must also clear the A flag for clients to not perform auto config of addresses (SLAAC).
The DHCP server must be correctly configured with a shared network where there are multiple prefixes on a  link - I can’t help with this more than I already have done as I’m new to Kea (I’ve been for decades, and still am, an ISC DHCPD user).
If a client wants addresses via DHCP from multiple prefixes, then it needs to ask for them - no, I do not know how this needs to be configured, and AFAIK this is still an “unsolved problem” in general.
NOTE - this is not IPv6 not implementing something available in IPv4, it simply is a case of IPv6 supporting more functionality and not all the permutations having been worked out yet. For example, if you constrain yourself to one single prefix on a link then you’ll find DHCP working more or less the same for IPv6 as it did for IPv4 - except for support of more than one address being allocated.


I have no intention of investing any more time in this thread unless you choose to accept advice and be civil.


Simon