Category Archives: Linux

Ansible & Cisco – Automating configuration management.

Configuring network equipment has always been somewhat of a tedious affair. Copy and pasting a configuration file through the console port doesn’t scale (or you need a lot of interns!) and other solutions like Cisco Prime are slightly overkill if you only want to change a few lines of configuration.

This is where Ansible comes to the rescue. Originally built as a Linux Configuration Management Tool, in the vein of Chef/Puppet/Salt, it’s built around an SSH agent-less push model. Directly using the SSH connection, it’s remotely executing command you define in “Playbooks” This is why it’s a great fit when it comes to network devices as those are still telnet/SSH based. API/Netconf are starting to be more and more common, but SSH is still present. Especially on older network equipment.

Recently, Ansible has been augmented with a series of module that allow a network operator to leverage Ansible to deploy configuration to remote equipment. For example, if you just realized that your template is mysteriously missing NTP, Syslog and SNMP configuration and there are about 40 pieces of equipment deployed – I’m not saying this totally happened to us – Ansible is here to help.

The following playbook does the following :

  • Define a role : cisco-ios-common – which holds all the default configuration that is used by our devices.
  • In our case, the SSH connection is initiated from the sysadmin computer running the playbook – but it can be adapted to run from a bastion host.
  • No need to gather facts.
  • Create the variable holding the credentials necessary for accessing the equipment.

The actual file with the tasks is fairly simple.

This is literally lines that are parsed from the “show running-config” command and compared to each task. If it’s not there, it’s added or changed . In this case, we configure the RO SNMP community and the NTP server. To be extra careful, we also take a backup of the running-config before applying the changes. Using the “provider” statement, we are referencing the variables defined in the playbook file. All other private variables can be stored in an Ansible vault file and encrypted.

With the appropriate inventory file I was able to quickly fix our deployment mistake without manually connecting to every single switch.

Raspberry Pi 2 – NTP server | Stratum 1

Well, it’s done! I have a small RP2 acting as a Stratum 1 NTP Server using a GPS module with the GPIO input.

It’s been added the canadian cluster of NTP servers and has begun answering queries. The process was relatively simple with a few things to keep in mind :

  • The default repository do not hold a recent image of the NTPD image. You are better off downloading and compiling the archive yourselves.
  • Here is the GPS module for the Raspberry Pi A+/B+/2 : Link
  • If you have an older Raspberry Pi : Link
  • You might need an antenna to lock on to the GPS signal. Especially true if you are indoors. Depending if a GPS repeater is present, it might be impossible to get a lock anywhere else than the top floor of a building or a room with windows.
  • I made the mistake of ordering the old style of GPS module for the RP2. It does fit, but it’s a bit awkward and I need to get a GPIO riser so that the antenna isn’t hitting the USB/Ethernet connectors. For now, the GPS module is just not fully connected to the GPIO board. There might be 3 centimeters of the connectors exposed. Everything seems to be working fine but doesn’t look very clean.

Here is a small taste of what kind of devices seem to be hitting my server :

tcpdump_ntp (

That’s a lot of cable modem/CPE devices. I wonder why ISP are not using internal servers. Seems like time is something you would want full control over.


Centos 6.5 – Monitoring Bind9 with Bindgraph.

Bindgraph is a program based on Mailgraph and offers the same basic features. It reads the dns_queries.log file and creates a .rrd file listing the number of queries per record type (A, AAA, CNAME, PTR and a few others). It then generates a graph, takes a screenshot and creates a nice HTML page with a .cgi script.

It provides quick overview of your dns traffic. Though, it is limited to the number and type of queries and does not handle where they come from.

Day View

2014-10-12 18_05_00-DNS Statistics for

Month View

2014-10-12 18_05_50-DNS Statistics for


1) Launching the daemon :


CentOS 6.5 – Create a Certificate Authority

yum install easy-rsa
Default Directory : /usr/share/easy-rsa/2.0/


CentOS 6.5 – Private key authentication for ssh

SSH is secure! I don’t need anything else!

Well, you are not exactly wrong. But security is not something that should be taken lightly.

I’ve recently acquired a Linode host and I was stunned by the number of unauthorized login attempts. About 99% of those attempts were probably automated scripts crawling the Internet for anything responding to queries on port 22. I believe that a huge part of modern “hacking” is entirely automated which reinforces the perspective that security is a 24/7 concern.

Since SSH is your main entry point to control your machine, it’s especially critical that it’s well protected. Private/public key authentication allows you to login into your machine without providing a password.

Here is a very basic overview.

You first create a key pair : Private and Public key. The private key allows you to apply your “signature” to content. The only way to verify that signature is to have your Public key. You then transfer that public key file unto your server. When you try to connect to the server using your Private key, the server will try to match the unique signature using the Public key you had previously transferred. That entire operation completely removes the need to transfer a password. It’s almost much more complex to brute-force.

That said, it’s up to you to protect your private key. I recommend adding a passphrare during the key generation. Without that extra step, both the public and private key would both be written in clear-text.

China is knocking…

Jun 16 02:12:30 li362-86 sshd[2234]: Failed password for root from port 32848 ssh2 Jun 16 02:12:31 li362-86 sshd[2232]: Failed password for root from port 29883 ssh2 Jun 16 02:12:32 li362-86 sshd[2234]: Failed password for root from port 32848 ssh2 Jun 16 02:12:34 li362-86 sshd[2232]: Failed password for root from port 29883 ssh2 Jun 16 02:12:34 li362-86 sshd[2234]: Failed password for root from port 32848 ssh2 Jun 16 02:12:36 li362-86 sshd[2232]: Failed password for root from port 29883 ssh2

Prerequisites : This guide was performed on a CentOS 6.5 machine with almost no extra packages. Most, if not all commands, should be the same on Debian based OS. That said, be aware that you will have to substitute your own folder and files path. Any variable you need to replace with your own will be marked with the “$” sign.

Folder has to be owned by the appropriate user attempting to log in.

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CentOS 6.5 – Mumble and Django-Mumble

Mumble – Open source voice server

Django Mumble – Open source django based administration interface