Revision as of 03:29, 25 February 2013

Alternative Network Setup

These are notes on macvlan on a box with real vlans. The goal here is to have the host on a management vlan, and several guests each on other vlans. There's no need for the host to talk to the guests. The host resides on the "OOB" network, and if the host needs to talk to a guest, it does so with lxc-console, like having a KVM. Each guest should get its address from the DHCP server on the appropriate vlan.Something like this:

Setup:

host	dhcp on vlan 8
guest1	dhcp on vlan 64
guest2	dhcp on vlan 129
guest3	dhcp on vlan64 (different address)

Host's /etc/network/interfaces file

auto lo
iface lo inet loopback
 
# MGMT vlan
auto eth0.8
iface eth0.8 inet dhcp
     hostname lxchost

# USR vlan - we bring it up, but dont assign an address
auto eth0.65
iface eth0.65 inet manual
   up ip link set $IFACE addr de:ad:be:ef:ca:fe
   up ip link set $IFACE up
   down ip link set $IFACE down

# VoIP vlan - we bring it up, but dont assign an address
auto eth0.129
iface eth0.129 inet manual
   up ip link set $IFACE addr 0f:f1:ce:c0:ff:ee
   up ip link set $IFACE up
   down ip link set $IFACE down

Here's /etc/lxc/lxc.conf

lxc.network.type   =   macvlan
# Allow guests on the same vlan to see each other                                   
lxc.network.macvlan.mode = bridge                                                    
lxc.network.link   =   eth0.65                     
lxc.network.name   =   eth0                                                                   
# lxc.network.hwaddr = de:ad:be:ef:c0:00    # macvlan will make one up, but possible if wanted                 
# lxc.network.flags  =   up                 # Do NOT bring up the interface, we will do so within the container
# lxc.network.ipv4   =   0.0.0.0            # Do NOT assign an address, we do so within the container          
                                                                                                     
# Capabilities to drop (for instance, to stop the guest from mounting sys)   
# Taken from http://sourceforge.net/mailarchive/message.php?msg_id=28285704  
# sys_boot is not listed here, as it causes problems when the host tries to stop the guest

# If you trust the guest, then you can get by without dropping capabilities
                                                                                  
lxc.cap.drop= sys_admin audit_control audit_write fsetid ipc_lock                 
lxc.cap.drop= ipc_owner lease linux_immutable mac_admin mac_override mknod setfcap
lxc.cap.drop= setpcap sys_module sys_nice sys_pacct sys_ptrace sys_rawio
lxc.cap.drop= sys_tty_config sys_time

Create the guests

for a in `seq 1 3`; do 
  lxc-create -n guest${a} -f /etc/lxc/lxc.conf -t alpine
  ln -s /etc/init.d/lxc /etc/init.d/lxc.guest${a}
done

vi /var/lib/lxc/guest2/config

  change lxc.network.link to eth0.129

Start and enter the first guest (this is where the fun starts)

/etc/init.d/lxc.guest1 start
lxc-console -n guest1

Fun inside the guest

If you just start networking, you'll get:

cat: can't open '/sys/class/net/eth0/ifindex': No such file or directory
/usr/share/udhcpc/default.script: line 125: arithmetic syntax error
/usr/share/udhcpc/default.script: line 125: arithmetic syntax error

This is because /sys is not mounted, and we don't really want to do that.

Fortunately, there's a simple fix:

--- /usr/share/udhcpc/default.script.orig
+++ /usr/share/udhcpc/default.script
@@ -39,7 +39,7 @@
 }
 
 if_index() {
-	cat /sys/class/net/$interface/ifindex
+	cat /sys/class/net/$interface/ifindex || echo 0
 }
 
 calc_metric() {

Let's make the /etc/network/interfaces proper

 guest1:~# cat - << EOF >/etc/network/interfaces
   auto lo
   iface lo inet loopback

   auto eth0
   iface eth0 inet dhcp
       hostname guest1
   EOF

And add networking:

 guest1:~# rc-update add networking

And test

 ctrl-a q
 lxchost# /etc/init.d/lxc.guest1 restart
 lxchost# lxc-console -n guest1

We have Networking!
Repeat the patch and configuration for guest2 and 3

What Works, What Doesnt

Pro
- Each guest has its own mac address
- Network connectivity between each guest
- No communication allowed between host and guests (this is a plus in our case - managment vlan != user vlan)
- if iptables modules are loaded in the host, each guest can create its own iptables rules (awall for all! sweet)
Con
- No communication allowed between host and guests because we are not using a bridge interface (this is a plus in our case - managment vlan != user vlan)