hi,

> Could I have a NAT rule like
> 
> map lo0 x.x.x.x -> y.y.y.y
> 
> where y.y.y.y is an address of one of the external interfaces, and x.x.x.x
> an alias on lo0 ?
> 
> Would the packets then go to the wire from y.y.y.y without checksums?

although i'm not sure about ipfilter,
i don't think it goes to the wire if y.y.y.y is an address of
one of your own interfaces.

generally, if outgoing interface decision is changed from lo0 after
udp_output check it, it can be a problem.

YAMAMOTO Takashi