Questions[dhcpv6](server)

According to RFC3315:

Each DHCP client and server has a DUID. DHCP servers use DUIDs to identify clients for the selection of configuration parameters and in the association of IAs with clients. DHCP clients use DUIDs to identify a server in messages where a server needs to be identified.

[...]

Clients and servers MUST treat DUIDs as opaque values and MUST only compare DUIDs for equality. Clients and servers MUST NOT in any other way interpret DUIDs.

For IPv4 it's very common for a DHCP server to allocate fixed addresses to clients based on, for example, MAC addresses. So for IPv6 how does the DHCPv6 server allocate fixed IPv6 addresses?

I have two virtual machines with Ubuntu Server 20.04. One of these virtual machines is a DHCPv6 server, and the other one is a client. I am able to set an IPv6 address on the client, but I cannot ping to and from this address. ip -6 route shows this address but with prefix length of 128. I would like to have the prefix length equals to 64, the same as the server IP address has. When I add to my routing table on the client IP address obtained from the server but with prefix length equals to 64, I can ping between my virtual machines.

This is my /etc/dhcp/dhcpd6.conf file on the server:

default-lease-time 2592000;
preferred-lifetime 604800;
option dhcp-renewal-time 3600;
option dhcp-rebinding-time 7200;
allow leasequery;
option dhcp6.name-servers 3ffe:501:ffff:100:200:ff:fe00:3f3e;
option dhcp6.domain-search "test.example.com","example.com";
option dhcp6.info-refresh-time 21600;

authoritative:
subnet6 fdaa:a:a:a::/64 {
   range6 fdaa:a:a:a::100 fdaa:a:a:a::199;
}

The last three lines were added by me.

This is my /etc/netplan/00-installer-config.yaml file on the client:

network:
   ethernets:
      ens3:
         dhcp4: false
         dhcp6: true
   version: 2

Thank you in advance for any help.

I'm currently working on adding IPv6 capabilities to our network, and I have some questions on what is considered best practice in 2020 to convert some of the IPv4 concepts we are used to into the IPv6 world.

In the current setup that I have, we are allocated a /64 from the ISP, and the router advertises that prefix for clients to configure themselves using SLAAC. This seems to work fine and as far as I know everyone has IPv6 internet access.

However we like to be able to query things by name, and I'm not sure what the best practice is to provision AAAA records for the clients.

What I have done is deploy stateful DHCPv6 on the dnsmasq instance that runs our DHCPv4 and tell it to hand out ULAs from some range which naturally provisions AAAA records for anyone who asks for an address. This also seems to work fine, but I know there is some dislike of stateful DHCPv6. This also helps me to consolidate the assignment of the servers we have on static IPs exactly as I do for DHCPv4, these servers for various reasons should be accessible at a fixed IP address and we would like that to continue to be the case for IPv6.

The only other way I can think of to do the AAAA records is to send the dnsmasq machine the RA prefix from the router via unicast and then use the dnsmasq to advertise the GUA prefix for slaac using the ra-names option. This wouldn't solve the static address assignments though as far as I can tell and I'm not sure how reliable it actually is. Is there a better way to handle internal AAAA records than ULAs with stateful DHCPv6?

Finally, as things are starting to work, we are now looking at migrating our public services to IPv6. My understanding is that this would require a fixed GUA for the servers to provision public AAAA records. I'm not sure how to achieve this using SLAAC from the edge router, unless there is some kind of dynamic-dns equivalent. Can I again use DHCPv6 or another manual assignment method to pick IPs in our assigned prefix? I was hesitant to do this because I thought it might collide with a SLAAC address and I'm not sure what happens if there's a collision. Alternatively I have the option to ask the ISP for a /48, should I do that and advertise a single /64 for local clients to get connectivity and different /64 for static servers? This seemed like overkill to me, we already wont come close to filling the single /64 but this might be my IPv4 mindset confusing me.

For IPv6, I understand clients may get an address either statelessly using SLAAC, or statefully using DHCPv6 (although I hear Android doesn't support address assignment via DHCPv6).

My question is, for clients that configure their IPv6 address via SLAAC, what is the way for a network to push other network configuration to them? Can they get such configuration through Router Advertisements, or must the network also deploy DHCPv6 for clients to get this extra information (but not get their IPv6 address)? Eg:

• DNS server
  • I hear RFC 6106 - IPv6 Router Advertisement Options for DNS Configuration is intended to provide a way for communicating DNS servers. In practice, do Windows, Linux, Android, iOS clients use RA or DHCPv6 to find IPv6 DNS servers?
• NTP server
  • I have found a draft for NTP advertising through Router Advertisements. But this draft was not accepted, I guess. So do clients need to find an NTP server via DHCPv6?
• SIP server
  • Do clients need to use DHCPv6 option 21 or 22? Is there any Router Advertisement equivalent?
• Vendor-specific protocols
  • DHCPv6 has option 16 and option 17 for vendor-specific information, which could be used by a client to find a vendor-specific server on a network, if the DHCPv6 administrator has configured it. Is there any Router Advertising equivalent?

If DHCPv6 is the only way to get this sort of server info, is it reasonably straight-forward to configure a client to get its address via SLAAC, and then get this extra configuration via DHCPv6?

isc-dhcp-server now supports rfc6939 as of version 4.3, and I would like to be able use it as it is quite nice to be able to just use the mac address to identify dhcpv6 clients. However, I can't seem to find a dhcpv6 relay that supports rfc 6939, option 79, or dhcp6.client-linklayer-addr, other than the one on a Cisco switch as in this article:
https://insinuator.net/2015/02/is-rfc-6939-support-finally-here-checking-the-implementation-of-the-client-link-layer-address-option-in-dhcpv6/

I imagine the isc-dhcp-relay should be able to do this since isc-dhcp-server does, but it doesn't out of the box and the man page on ubuntu 16.04 server doesn't mention a way of turning it on. Does anyone either know how to enable this option, or know of a dhcpv6 relay that is installable on linux that does support it.