Just two quick questions:

• What's the meaning of that ones <= 80?
• Do we need the bool variable or can we just if ones <= 80 { NetworkOptionDeferIPv6Alloc(true) }?

@icecrime
When IPv6 support was added into docker, the IPv6 address assignment could happen in two ways:

• from MAC address (last 48 bits of the IPv6 address == MAC address)
• or via ip allocator

The first method was the preferred way, always chosen by bridge driver when the IPv6 network had enough host bits to contain the MAC address. That's from where the 80 (128-48) bits comes from.

This logic gave a backdoor access to configure deterministic IPv6 addresses for containers.
In order to restore that behavior (which got broken) only for the default bridge network, I had to bring the 80 bits in here.
Whenever we support the IPAM options for endpoint (container), we can deprecate the above behavior.

Since the ones are not visible outside of the if scope, I opted for a bool variable outside.
If I had to initialize the NetworkOption setter function inside the if scope, then I'd need to define anyway an extra variable outside, of type libnetwork.NetworkOption. Hence I did not see a difference.

Thanks for the background, I think it's worth a code comment (or people reading this will definitely scratch their heads).

I don't really understand why you would need a variable if you just called libnetwork.NetworkOptionDeferIPv6Alloc at that point of the code, but I'll trust you with that :-/