UML networking on Salix

[GJones]

One of the awesome things about User Mode Linux is that it doesn't require anything special on the host system; it just runs. At least in theory... In practice, things may be harder.

As an experiment I have downloaded prebuilt images of user mode kernel 3.3.4 and CentOS 6.x. Booting into this system

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$ ./kernel64-3.3.4 ubda=CentOS6.x-AMD64-root_fs mem=512M

works fine. However, tun/tap networking is very difficult to set up. I've done the following:

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# modprobe tun
# modprobe iptable_nat
# iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
# echo 1 > /proc/sys/net/ipv4/ip_forward
# chown root:users /dev/net/tun

But when I boot UML like this:

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./kernel64-3.3.4 ubda=CentOS6.x-AMD64-root_fs mem=512M umid=uml1 eth0=tuntap,tun0

and run dhclient on the resulting ethernet interface, I get the following error:

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[   45.760000] TUNSETIFF failed, errno = 1
RTNETLINK answers: Operation not permitted

1. What am I doing wrong?

2. Is there any easier way to set up networking with UML?