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Tap
The tap networking backend makes use of a tap networking device in the host. It offers very good performance and can be configured to create virtually any type of network topology. Unfortunately, it requires configuration of that network topology in the host which tends to be different depending on the operating system you are using. Generally speaking, it also requires that you have root privileges.
Executar o QEMU como um usuário fornece uma rede simplificada. De acordo com um artigo do WikiBooks
If no network options are specified, QEMU will default to emulating a single Intel e1000 PCI card with a user-mode network stack that bridges to the host's network. The following three command lines are equivalent:
qemu -m 256 -hda disk.img &qemu -m 256 -hda disk.img -net nic -net user &qemu-system-i386 -m 256 -hda disk.img -netdev user,id=network0 -device e1000,netdev=network0 &The -net option is superceded by -netdev in newer QEMU versions.
The guest OS will see an E1000 NIC with a virtual DHCP server on 10.0.2.2 and will be allocated an address starting from 10.0.2.15. A virtual DNS server will be accessible on 10.0.2.3, and a virtual SAMBA file server (if present) will be accessible on 10.0.2.4 allowing you to access files on the host via SAMBA file shares.
User mode networking is great for allowing access to network resources, including the Internet. By default, however, it acts as a firewall and does not permit any incoming traffic. It also doesn't support protocols other than TCP and UDP - so, for example, ping and other ICMP utilities won't work.