user-mode networking daemons for virtual machines and namespaces

 passt implements a translation layer between a Layer-2 network interface and
 native Layer-4 sockets (TCP, UDP, ICMP/ICMPv6 echo) on a host. It doesn't
 require any capabilities or privileges, and it can be used as a simple
 replacement for Slirp.
 .
 pasta (same binary as passt, different command) offers equivalent
 functionality, for network namespaces: traffic is forwarded using a tap
 interface inside the namespace, without the need to create further interfaces
 on the host, hence not requiring any capabilities or privileges.