Did not get any response in the CentOS Virt list.

Posting in the CentOS General list hoping that some one here can provide clarification.

Thx, -- Arun Khan

---------- Forwarded message ---------- From: Arun Khan Date: Tue, Jun 12, 2012 at 8:54 PM Subject: Meaning of "vlan=" and "name=" in Linux KVM To: CentOS Virt centos-virt@centos.org

Greetings KVM gurus,

I am trying to understand a "use case" scenario for the "vlan=n" option and "name=name" for the "-net nic" and "-net tap" directives.

I have done some search but I have not come up with anything that sheds any light on the above.

<quote from kvm man> Network options:

-net nic[,vlan=n][,macaddr=mac][,model=type] [,name=name][,addr=addr][,vectors=v]           Create a new Network Interface Card and connect it to VLAN n (n = 0 is the default). The NIC is           an e1000 by default on the PC target. Optionally, the MAC address can be changed to mac, the           device address set to addr (PCI cards only), and a name can be assigned for use in monitor           commands.  Optionally, for PCI cards, you can specify the number v of MSI-X vectors that the card           should have; this option currently only affects virtio cards; set v = 0 to disable MSI-X. If no           -net option is specified, a single NIC is created.  Qemu can emulate several different models of           network card.  Valid values for type are "virtio", "i82551", "i82557b", "i82559er", "ne2k_pci",           "ne2k_isa", "pcnet", "rtl8139", "e1000", "smc91c111", "lance" and "mcf_fec".  Not all devices are           supported on all targets.

-net tap[,vlan=n][,name=name][,fd=h][,ifname=name] [,script=file][,downscript=dfile]           Connect the host TAP network interface name to VLAN n, use the network script file to configure           it and the network script dfile to deconfigure it. If name is not provided, the OS automatically           provides one. fd=h can be used to specify the handle of an already opened host TAP interface. The           default network configure script is /etc/qemu-ifup and the default network deconfigure script is           /etc/qemu-ifdown. Use script=no or downscript=no to disable script execution.

</quote from kvm man>

My objective is to create a small "virtual" network using bridges/tap interfaces on the Host OS and running the Guest OSs (the network segment separated by vlan=somenumber)

My hypothesis is that with "vlan=X" and "name=somename" the VMs can be separated into different segments i.e. a set of tap interfaces on vlan=10 and another set of tap interfaces on vlan=20 connected to the same bridge br0.

I have two VMs started with  "kvm  -net tap,vlan=10" and "kvm  -net tap,vlan=20" respectively but with IP numbers in the same subnet 172.16.0.0/24; they are able to ping each other with different "vlan" numbers.

I would appreciate any clarification on the "vlan=" and "name=" options. Sample script for my KVM VMs

<script> #!/bin/bash

kvm \ -vga std \ -m 1024 \ -cpu core2duo \ -smp 2,cores=2 \ -drive file=/home/kvmusr/KVM/vdisks/centos62.img,index=0 \ -net nic,vlan=1,model=e1000,macaddr=${nic_mac_addr0} \ -net tap,vlan=1,ifname=tap0,script=no,downscript=no \ </script>

Thanks, -- Arun Khan