What happens if you try two commands ‘ethtool -p ‘ and ‘ethtool ‘ in parallel.

If you start 'ethtool -p ' and also start 'ethtool ' after that, you may see the delays in 'ethtool ' command. It is because any ethtool commands start by taking 'rtnl_lock' and 'ethtool -p' is keep running for LED on/off. In the below, bnx2x's identity function just turns on or off the led. get_settings()… Continue reading What happens if you try two commands ‘ethtool -p ‘ and ‘ethtool ‘ in parallel.

External network doesn’t work in OpenStack running on VMWare fusion?

I've been hard time to figure out why my openstack doesn't communicate with outside and it's always saying 'Down' when I checked external network in router. It turned out that is the issue with 'promiscuous mode'. In default, it's requires to have authentication for entering promiscuous mode. By turning it off, the network works fine… Continue reading External network doesn’t work in OpenStack running on VMWare fusion?

How to use fixed DHCP address on VMware Fusion 4/5

There's a time you want to use fixed address even for your NATed VM guest. In the case of VMware, you can achieve this by modifying configuration file in '/Library/Preferences/VMware Fusion/vmnet8'. vmnet8 is the virtual interface for NATed guests. You can find what ranges are currently applied for this virtual guests by checking dhcpd.conf. $… Continue reading How to use fixed DHCP address on VMware Fusion 4/5

Creating virtual networks with NetworkManager

In Linux, you can create a virtual network - aka. vlan. To create it you need to create a file under /etc/sysconfig/network-scripts/ directory. For example, if you want to create a virtual network for eth0, you need to create a file something like below. Here I created with a tag 0. $ cat /etc/sysconfig/network-scripts/ifcfg-eth0:0 DEVICE="eth0:0"… Continue reading Creating virtual networks with NetworkManager

[BASH] Check dropped RX packets

This is a simple bash script to check whether NIC is dropping packets or not. It works with only one NIC card at one time because there's possiblity that packet can go through another NIC. #!/bin/bash NET_ON_LIST=`ifconfig | grep "Link encap:Ethernet"` NET_ON_COUNT=`echo "$NET_ON_LIST" | wc -l` if (($NET_ON_COUNT != 1)); then echo "Need to set… Continue reading [BASH] Check dropped RX packets

Configuring a Bridge Interface for the KVM-based virtual machines

If you are going to run virtualized host as a web server or some services for the clients, the systems should be accessible from the outside. Unfortunately, the default network configuration in KVM is NAT (Network Address Translation). It is good for some VMs who will co-work with other VMs, but for the server, it… Continue reading Configuring a Bridge Interface for the KVM-based virtual machines

Set up test environment with two virtual machines.

To test some problems usually I have to have two machines which is not easy to have. Especially if I have to configure it for each version, RHEL4, RHEL5, Fedora, etc. Virtualzation comes here to solve those kinds of difficulty. But, just installing new operating system each time is also not a perfect solution. You… Continue reading Set up test environment with two virtual machines.