Monday, November 15, 2010

Upgrading CentOS 5.4 to 5.5 32Bit DomU on a Xen 64 Bit Dom0

Normally upgrading centos is very simple by doing a
yum update

But when you run centos as a 32bit DomU under a 64 Bit Dom0 server, you will receive strange error messages.
This is due to the fact, that the rpm command looks at the installed kernel, and that one is a 64bit build. So it then trys to move everything to 32 AND 64 bit.
To prevent this, just create the file /etc/rpm/platform and place the line:
in it.
After this, all the yum rpm commands work fine, since they are fixed to the i386/i686 platform. No confusion about the 64bit kernel.

Wednesday, November 10, 2010

ipv6 in the wild

In the last year we did many steps toward ipv6 enabling our networks and servers.
Many things are simple, but there are also many pitfalls.

Here some infos about ipv6 in Ubuntu/Debian

- The Ubuntu distribution 9.04 and newer have good IPv6 support, most applications work with ipv4 and ipv6. Some applications however have problems with ipv6 addresses in some places. Here a upgrade to the most recent 10.10 release solves many issues.

- Debian, yeah, most things work fine in lenny, you can do most things you need, but there are still a few places where you may stumble. The real "full" ipv6 support is coming up in squeeze.

Here a two places where you might struggle:

- Assigning a static IPv6 address in debian lenny just does not work....
Nothing to worry about on workstations/desktops, but on firewalls and servers... it would be nice to always have the same ipv6 address assigned.
The reason for the problem is, that when the eth0 interface (or any other) is activated, the kernel module ipv6 is not yet loaded. So it's not possible to assign the ipv6 settings specified in the /etc/network/interfaces file.
The simplest solution is to just add ipv6 to the file /etc/modules (and rebuild the initramfs), that way ipv6 is directly loaded on boot and everything works as intended.

- RSYNC has only partial ipv6 support.
What does this mean ?
Rsync is able to resolve host names into ipv6 addresses and then connect to them via ipv6.
But if you with to specify the ipv6 address of the host directly on the commandline, then it fails parsing the address.
The simplest way to solve the problem is to install the rsync from the debian backports.

Don't forget, ipv4 addresses are running out in the next year, so prepare slowly to add ipv6 support to your network.
You don't have to do it in a big-bang way, rather just implement it step-by-step.