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I have 2 NICs: eth0 & eth1 on a host OS which runs some VMs (LXC) under it.

  • The hosts eth0 is connected to a private network and configured as the primary interface.
  • The hosts eth1 is connected to the DMZ.
  • Each VM has a static IP that bridges to eth0 on the host.
  • Some VMs, which need a public IP, have a 2nd virtual NIC bridged to the hosts eth1.

Question:

  • Can I remove the IP address on the hosts eth1 NIC? The host has absolutely no need for a public IP address, I only need to bridge the interface to selected guest VMs. It's the guest VM which will host a service on whatever public IP its assigned.

Cursory attempts at removing the IP on the hosts eth1 have generated errors.

2
  • You might be interested in this question.
    – TNW
    Apr 16, 2013 at 11:17
  • 1
    Have generated what errors? Apr 16, 2013 at 11:37

2 Answers 2

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It should work, as long the interface is still up

ifconfig eth0 | grep UP
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

the bridge is a "switch" and it doesn't need to have one IP. But please check if you have firewall rules in eth0:

iptables -l -vnx

if rp_filter is off

 cat /proc/sys/net/ipv4/conf/eth1/rp_filter
 0

and if all fails, try to enable the STP:

 brctl stp br0 on

and enable the promisc mode in that interface:

  ifconfig eth0 promisc 

(ifconfig eth0 -promisc to remove it)

Of course, also check if there is no other config using that removed IP :)

1

Yes it works.

It depends on your operating system on how to configure such a network setup in a way that the bridge is up and running after a reboot in that constellation.

From my experience:

  • SLES10 SP4: Works - do not use yast2
  • SLES11 SP2: Works - use mv to rename the bridge to something useful after setup with yast2
  • Ubuntu 10.04 LTS: Works only manually - Ubuntu keeps setting a dummy-IP.
  • RedHat 5: Works - use vi.

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