Tech@Sakana – A sysadmin’s blog

My new center of interest those days being virtualization, I tried quite a few software starting with Xen, then QEMU, then KVM, and finally VirtualBox. But as far as giving a network access to the VM is concerned, I’ve always sticked to a network bridge for the reason that this makes the VM appear on the network just like any other computer of your network.

This post provided a sample script to setup a bridge suitable to use with all of the named virtualization softwares.

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photo credit: saschaaa

This posts gives a short intro about VLAN and a simple configuration sample on a DELL PowerConnect 5224 switch with an OpenBSD machine.

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If you are looking for a procedure to reset the password of a Dell PowerConnect switch, you’ll find it at the Dell support forum in the following thread : PowerConnect Password Recovery Procedure for managed switches.

As far as the 5224 is concerned, you mostly have to hold Ctrl-F from the power-on till the end of the boot of the switch, which will bring the “reset to factory ?” question and solve the problem of the lost password.

The User Guide for the 5224 is available online.

A bit of context : I have a bind 9 DNS allowing DNS updates from clients on the LAN (ok this is fairly insecure, but still my LAN is my home LAN composed of 4 machines … let’s say that’s good enough for me ! )

The named.conf allows those updates with this config directive in the zone config block :

allow-update {mynet; };

and mynet is defined an acl directive to be my LAN.

Then you can update your DNS with the nsupdate tool with a syntax along the following lines :

spaghetti:~# nsupdate
> server 192.168.0.1
> update delete spaghetti.domain.name A
> update add spaghetti.domain.name 8000 A 192.168.0.103
> send
> quit

I was then looking for a place to hook a code snippet doing that update after an update via DHCP and I found the answer in A dynamic dns update client on Debian with dhcp3-client (many thanks dude !).

Here is the drill down :

1. install the dhcp3-client package (apt-get install dhcp3-client ): this version has easy to use hooks before and after querying the DHCP server to get network config
2. you can drop a script which will automate the nsupdate in “/etc/dhcp3/dhclient-enter-hooks.d” and it will get run right after network configuration (see the sample debug script for the variable which are available upon script execution, such as $new_ip_address)

Windows XP

To see multicast group memberships in Windows XP, you can use netsh :

U:>netsh interface ip show joins
Interface Addr   Multicast Group
---------------  ---------------
192.168.139.1    224.0.0.1
192.168.137.1    224.0.0.1
192.168.136.1    224.0.0.1

Solaris (and probably other Unixen as well)

In Solaris, the netstat command can be used :

$ netstat -g
Group Memberships: IPv4
Interface Group                RefCnt
--------- -------------------- ------
lo0       224.0.0.1                 1
eri0      224.0.0.1                 1
$