Questions: implementation of WSL 2 networking

[cerebrate]

• Your Windows build number: 18945

This is more of a series of questions/discussion items than an issue - some of which may well relate to Hyper-V and network namespaces, per #4304 - but a few things have occurred to me to ask after assorted fiddling done in the wake of my network issues ( #4342 ). The whole of the thing, really, is a request for a quick outline of how networking's implemented in WSL 2, but these are some specific questions I had:

• How does the WSL 2 interface get its IP address? It's not configured statically Linux-side, and it doesn't appear to be using DHCP, so where does that come from?
• Could it be made to use DHCP (which also I suppose is the "why doesn't it?" question? In my flailing around with [WSL 2] No network connectivity after upgrade to 18945 #4342 I observed that a DHCP client inside WSL 2 is perfectly capable of picking up an address, etc., if the WSL virtual switch is bridged to the external network, so it seemed a little odd that it wasn't)?

(I don't have a particular need for this ATM, but I note that in this brave new systemd world, mDNS support, et. al., is build into systemd-resolved rather than using avahi-daemon and can't be turned on except on interfaces configured by systemd-networkd, which so far as I can tell can either entirely ignore the WSL 2 eth0, or else can break it by not being able to get a DHCP IP. It can't set some settings and leave others alone.)

• I'm curious as to the reasoning behind WSL 2 using a NATted network rather than just bridging to the existing external network; would appreciate any insight. Is it just as a step towards unifying the IP addresses with the Windows host?
• Are there any current major barriers to IPv6 support? That's something that I couldn't get to come up even with a bridged network, which seemed curious, as I have seen it work in Hyper-V VMs before now.

Thanks in advance.

[Biswa96]

The network uses some kind of DHCP. First the Windows/Hyper-V side NIC is created with a random IPv4 address and configuration (subnet, guest IPv4, DNS, gateway). WSL side IP address is automatically added in that configuration. If WSL (aka. guest/container) is terminated the Windows side NIC remains but WSL side IPv4 address is automatically picked up from previous subnet. More network information can be found in LxssManager.dll and computenetwork.dll.