On MPIO and In-Guest iSCSI

April 3, 2014

I recently had a “stimulating discussion”* with Tom about MPIO initiated from a virtualized guest OS to a new SAN I am installing, and the pros and cons there of. This is one of those situations where the constraints of the technology make sense in a physical situation, but look a bit odd virtualized, so I wanted to ensure that I had the best possible solution for my needs, with the least extra effort, and importantly, some logic to back up the decision.

More…

When IIS ‘Configure’ Files Truncate

April 2, 2014

Not so common problems

There is a subset of problems that happen very very rarely. That require a set of coincidences to occur in order for them to happen. The chances of these events actually happening are so small as to be negligible. In modern computing, they happen.

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Queued Exchange Mailbox Moves

July 2, 2013

This morning I had a list of Exchange 2010 move requests that were sat in a queued state. None in progress, but a few complete. So what was holding them up?

First I tried suspending/resuming them:

Get-MoveRequest -multitenant | suspend-moverequest -Confirm:$false

Get-MoveRequest -multitenant | resume-moverequest

That didn’t help.

Next I tried removing and re-creating the requests:

[PS] C:\scripts>Get-MoveRequest -MultiTenant | Get-MoveRequestStatistics | select displayname,exchangeguid,targetdatabase | export-csv moves.csv

[PS] C:\scripts>Get-MoveRequest -MultiTenant | Remove-MoveRequest -Confirm:$false

[PS] C:\scripts>Import-Csv .\moves.csv |foreach-object {new-moverequest -confirm:$false -Identity $_.Exchangeguid -targetdatabase $_.Targetdatabase}

But still no dice. The next thing I noticed though was that the moves were all targeted at databases on the same server, so I went hunting services on that machine. It turns out that the “Microsoft Exchange Replication” service was stopped. Kicked that into action, and bingo, 4 moves went to “In Progress”

 

How I nearly failed (part of) the CCNA again

June 17, 2013

A Little Bit of History

CCNA for me has been a long journey. I first saw the cert 8 or 9 years ago, and I’ve always fancied giving it a go, but never had the opportunity until my current role. I’ve managed to fail the combined CCNA exam twice so far, at my employers expense, and took a break to get some of the Microsoft Windows Server 2012 certs under my belt to keep us in line with Partnership levels. Now I’m back to the CCNA in earnest. Read the rest of this entry »

Centos and VMware tools

May 1, 2012

I found a funky blog post detailing the steps to get VMware tools from the official vmware repo. The details below are for 4.1 but it should be easy enough to tweak for other versions of ESX…

Thanks Emanuelis!

Add VMware GPG keys:

rpm --import http://packages.vmware.com/tools/keys/VMWARE-PACKAGING-GPG-DSA-KEY.pub
rpm --import http://packages.vmware.com/tools/keys/VMWARE-PACKAGING-GPG-RSA-KEY.pub

Edit /etc/yum.repos.d/vmware-tools.repo:

[vmware-tools]
name=VMware Tools
baseurl=http://packages.vmware.com/tools/esx/4.1latest/rhel6/$basearch
enabled=1
gpgcheck=1

Install VMware Tools:

yum install vmware-open-vm-tools-nox

 

CCNA – 1 – Purpose and Function

March 27, 2012

Introduction

This is the first post in a series as I work through the CCNA syllabus. The introduction to the series can be found here.

I will be pretty much following the CCNA Composite Exam Blueprint point for point. One post per bullet point. I’m using Version 11 (640-802).

Purpose and Function

The bullet reads: Describe the Purpose and Function of Various network devices

Various isn’t too well defined, but at least for this purpose we know that we are dealing with devices found in a small office or branch office networks. So, what devices do we have?

First we have the networking devices:
* Hubs
* Switches
* Routers
* Access Points
* Hardware firewall devices

These are the devices that make up the network itself.

Client Devices:
* Desktop and laptop computers
* Tablets
* Smart Phones

These are the devices that the network exists for, the devices that access the network and utilise it.

Finally we have service devices:
* Printers
* Servers
* Storage units

These are the focus of the network, the devices the users are trying to access.

These are very arbitrary groups, and I have picked them because that is how I think of them. Printers for example work very much more like a client in reverse, receiving data rather than requesting or sending it. In a SAN, servers act as client devices for the storage.

Broadly speaking though, the client devices connect either using wired, or wireless (more on both later) connections to the network devices. The network devices provide a transport system, usually with security in mind, for the clients to the server devices such that the clients can make a request, and the server devices can fulfil the request.

A small example of this? Why not. A user sat at a computer would like to be sure the computer has the correct time. The computer is connected to a switch, which is connected to a server which is running NTPd. The user sends a request, picked up by the switch and forwarded to the server. The server sends back the correct time, using the reverse route.

Now, lets take those network devices in a little more detail.

First we have the hub. Don’t see many of these, and I’ve never seen one in production use! A good place to start then. A hub is basically a repeater, like a parrot, everything it hears, it repeats. Any data in to any port is immediately sent out of all other ports. This means that each port on a hub is within the same segment, and collisions are more and more likely with more ports.

Hub, 1 segment, 1 collision domain.

Next the switch. A switch starts off like a hub, but for every request it receives, it remembers the MAC address of the requester, and the port the request came in on. That way, once a request destined for that MAC is seen, it only needs to be sent out of one port, not many.

Switch, 1 segment, many collision domains.

Routers work at the level above switches, effectively moving packets based on IP address, rather than MAC address. This makes each port on a router a separate segment, and by virtue of that a separate collision domain.

Router, many segments, many collision domains.

Access points are effectively hubs for wireless devices. Using the shared medium of the same “channel” of the spectrum each client device shares the bandwidth of the access point.

AP 1 segment, 1 collision domain.

I’ve rambled a bit there, and I haven’t touched on how full duplex cabling effects the collision domain with modern switches, or fun things like VTP and how to avoid switching loops.Fortunately, they come later in the blueprint.

So today I failed to achive a CCNA

March 23, 2012

What a depressing title for a blog. Why? That’s a good question. Why did I fail it? Why am I blogging about it? Showing the world what I can’t do? Well let’s start with the first question, and see if it takes us to an answer to them all. Read the rest of this entry »

The Road to Xen

September 13, 2011

Due to some not great clicking, and a ridiculously slow Internet connection in the office. I am left with one one way to get XenApp running, and not a lot of time. I have a .vhd, but no Hyper-V machine to test on… Time for some nesting.

Starting with William Lam’s instructions on virtuallyGhetto I spun up a Windows Server 2008R2 VM, installed and swapped over to the ESXi5.0 virtual hardware. Once I’d gotten past forgetting to make the Host config change:

echo “vhv.allow = \”TRUE\”” >> /etc/vmware/config

I had a booting windows box and a happy feeling. I installed the Hyper-V role, and rebooted. Then I realized I didn’t have any NICs and the fun started. Lots of black screens later I realized that if I boot the VM with NICs added, but not “Connected” everything is fine, and once I get the proper video feed from Windows, I can connect the BICs, and Hyper-V is happy. If I leave the NICs connected at boot though, I get a black screen. Very, very odd.

So, spwan a VM, attach the VHD, boot, and we have a XenApp virtual machine. Add it to DNS, and then….Hmmm… Getting a random error.

Perhaps I’ll be back later…

Nesting

After this, it's turtles all the way down....

Gentoo, Pacemaker, and Apache

March 22, 2011

I’ve been playing around with creating HA Load Balancing Proxy servers with Apache on top of Pacemaker today.

Since Gentoo does it’s configuration a little differently than most distributions, this hit a hurdle.

Gentoo puts some Apache command line options in a file /etc/conf.d/apache2 these decide the vohosts that start and other “-D” values. Without these apache will fail to start.

As Pacemaker doesn’t know about this file, or these values, apache was failing to spawn, and I was getting an error.

Simply copying the -D values, into the HTTPOPTS variable in the /usr/lib/ocf/resource.d/heartbeat/apache file fixed the problem:

HTTPDOPTS=”-D DEFAULT_VHOST -D INFO -D SSL -D SSL_DEFAULT_VHOST -D LANGUAGE -D STATUS -D PROXY”

Now I have two load balancers, running in an active/passive configuration…

The Journey to IPv6 – Part One – The Request

March 9, 2011

Hopefully this will be the first in a series of posts exploring the testing and implementation of IPv6 in the network I administer. My ultimate goal is to have our public facing web servers dual stack, and accessible by both IPv4 and IPv6.

For the moment, I have a request in to our ISP for a /56 block which should be actioned in the next couple of days.

Wish me luck!