Networking

NIC Discovery on CentOS

When adding a NIC to CentOS, one normally expects to see the device appear in /etc/udev/rules.d/70-persistent-net.rules. But things don’t always go your way.

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Kali on ChromeBook

http://www.kali.org/wp-content/uploads/2013/03/k-blog.pngI recently purchased a Samsung ChromeBook. Not for ChromeOS, but for the fact that Kali Linux – the network pen-test successor to BackTrack – announced a ChromeBook build. I figured I couldn’t go wrong with $250 for a Linux wireless ultra-portable dedicated to network testing. Turns out perhaps I could go wrong. (continue reading…)


Lost Network When Upgrading To ESXi 5.1

After upgrading from ESXi 5.0 to 5.1, I was presented with a curious “change has been detected” message during VM startup. It asked whether the VM had been recently “Moved” or “Copied”. I was leaning towards “Moved”, except for the fact that it also said “when in doubt, select ‘Copied'”. Big mistake picking ‘Copied’.

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Keeping Track of iSCSI LUNs as Multipath Devices

The Dell MD3200i is a very flexible mid-level iSCSI SAN. With 12 bays (up to 3TB NearLine SAS in each) and dual quad-port controllers, it offers excellent redundancy, capacity, and expandability. The Windows or Linux MD Storage Manager provides a decent GUI from which to define disk groups of various RAID styles and virtual volumes within each disk group for future filesystems.

But for all the labeling controls that MDSM offers for groups and volumes, the LUN mappings (to allocate volumes to iSCSI IP connections) are the real exposed labels. No matter how anal-retentive you get with group/volume hierarchy, all the ‘naming’ that the iSCSI initiators will ever see are the LUN numbers 0-31.

In an iSCSI system, there could be multiple ways to reach LUNs (via multiple network interfaces). For this reason, multipath support is used to provide route management and redundancy. On CentOS, filesystems are accessed via the multipath /dev/mapper device naming, mapped to the ‘physical’ iSCSI LUN. How are these mappings managed? ‘mpatha‘, ‘mpathb‘, ‘mpathc‘, etc are assigned first-come first-served to LUNs in the order they are discovered. This can make it difficult when adding multiple LUNs at the same time, because it is not entirely obvious which /dev/mapper/mpath device corresponds to which partition (despite all that effort you employed in creatively naming your MD3200i groups and volumes).

Because of my momentary confusion in regard to this LUN mapping, I thought that I would document the iSCSI implementation steps as performed on CentOS 6:

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An Overview of Network Monitoring

Every fledgling network administrator eventually comes face-to-face with the question “how do I monitor my network?”. But “monitoring a network” means different things to different people, and if you ask a crowd of experienced network managers for tool suggestions, it is highly likely that you will get a few misleading recommendations simply because the what-to-measure is not in alignment with your objectives.

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