Implement stateful DHCPv6 in forkdhcp

[defect-track]

Is there an existing issue for this?

• [x] There is no existing issue for this feature

What are you currently unable to do

This feature request is based on the following forum thread https://discuss.linuxcontainers.org/t/no-ipv6-for-incus-oci-containers/21086

In general you can work with dynamic IP addresses but for some services like DNS it is recommended to use a static IP. With the latest release 6.11 we can now configure custom DNS for OVN, bridge, etc. networks which is great. Trying to setup an OCI DNS on a static IPv6 only network. Current workaround is to have IPv4 enabled or use an container.

What do you think would need to be added

From my understanding of the forum topic stateful IPv6 support for OCI images.

[davidbockelman]

Hello, I'm a student at UT in Professor Chidambaram's Virtualization course. Could me and my partner take on this issue?

[stgraber]

For sure!

[davidbockelman]

Hello, our professor has advised us that this issue is harder than we initially thought, so we have chosen different issues to work on. I hope this doesn't cause you any inconvenience.

[stgraber]

Okay. I unassigned you.

For anyone else looking at this one, it should actually be pretty simple. We have a very minimal DHCP client in cmd/incusd/main_forknet.go (skip through all the C stuff, it's not relevant to the DHCP client, it's the RunDHCP struct and functions you want).

The current DHCPv4 client is implemented by using github.com/insomniacslk/dhcp which has support for both IPv4 and IPv6 DHCP client, so wiring up a basic stateful DHCPv6 client should be pretty straightforward unless there's something particularly different from their equivalent DHCPv4 client.

[rahafjrw]

hi! I'm a student at UT Austin's virtualization course and my partner and I were hoping to take this issue on. Can this be assigned to us? thank you!

[orcadennis]

I'm in the group with rahafjrw, could I also be assigned this issue?

[stgraber]

Done!

[rahafjrw]

hello! I wanted to clarify--how do we know whether to set up a DHCPv4 client or a DHCPv6 clients? Specifically, in RunDHCP line 308, "client, err := nclient4.New(iface)" is executed. How do we determine whether to use nclient4 vs nclient6? Thank you in advance!

[stgraber]

We don't really know, so we'll just run both.

[stgraber]

Technically Incus can tell in some cases and could pass us that information as arguments, but for now, let's just make it easy and have both DHCPv4 and DHCPv6 running.

[rahafjrw]

hello! I wanted to run our approach by you before we implement it. We were thinking we would define a new function that takes in a client that we then call twice inside of RunDHCP--once with the DHCPv4 client and with the DHCPv6 client. This function would pretty much contain the functionality that's currently in RunDHCP. Are we missing anything/is there something else we need to add or consider?

[stgraber]

Right so the problem is that RunDHCP is a blocking function as it goes into an infinite renewal loop at the end.

The main guiding principles here should be:

• Neither client should block the other. If running on a network with just DHCPv4, we shouldn't get stuck waiting for DHCPv6 and vice-versa.
• Network configuration for the given client should be applied once the first lease is received, this means applying the IP address and any provided routes.
• Background renewal of the lease must be handled.
• DNS configuration (resolv.conf) needs special care as that file contains data coming from both DHCPv4 and DHCPv6, so neither client functions can directly write it.

The way I'd probably tackle this is by:

• Adding two new fields to the cmdForknet struct. dhcpv4Lease and dhcpv6Lease, both pointers to the relevant DHCP Lease struct.
• Adding new dhcpRunV4 and dhcpRunV6 functions to the cmdForknet struct. Those will setup the relevant client, perform the initial DHCP request, apply the IP config and handle lease renewal.
• Adding a new dhcpApplyDNS function which will look at both dhcpv4Lease and dhcpv6Lease to generate the resolv.conf file. This function will be called by both dhcpRunV4 and dhcpRunV6 after they acquire a valid lease and have put a pointer to it in the shared struct.
• RunDHCP would then just handle bringing up the interface and reading the hostname before calling both dhcpRunV4 and dhcpRunV6` inside of Go routines, using Go channels to block until both clients have returned an error before exiting the process.

[rahafjrw]

got it, thank you!!