Can I bridge IPv4 while routing IPv6 on the same two interfaces?

Solution 1:

Bridging is a layer-2 thing. Aliasses on interfaces are for assigning multiple IP addresses: that is layer-3...

What you want is a brouter. See http://ebtables.sourceforge.net/examples/basic.html#ex_brouter

Solution 2:

Aliases are deprecated and basically meaningless. They exist solely to support adding multiple ip addresses to a single interface with the also long deprecated ifconfig command. They're not real interfaces. You can add multiple ip addresses to a single interface with the 'ip addr' command.

Using ifconfig is really a bad idea since it basically uses obsolete kernel interfaces that need to outright lie for some slightly more complex setups. This is unavoidable due to there simply not being a way to provide a correct answer within their limited flexibility.

This also means that bridging aliases is meaningless. Aliases don't really exist, they're just some (obsolete) syntactic fluff over the underlying interface (to trick ifconfig), so can't be meaningfully bridged (though the underlying interfaces can be).

That said, see https://unix.stackexchange.com/questions/432967/how-can-i-bridge-ipv4-but-route-ipv6-at-the-same-time