OpenVSwitch (OVS) is the pillar used by several emblazoned software, such as OpenStack or Red Hat's OpenShift to set up their Software Defined Networks (SDN): it enables users to quickly and easily implement multiple bridges to which connect Virtual Machines or Containers.

These bridges can be left standalone, creating isolated networks, or interconnected to the machine (or VM) NICs, providing bidirectional access to the network segment the NIC is connected to. In addition to that, it also enables the set up VxLAN Tunnel EndPoint (VTEP) on these bridges, enabling interconnecting OVS bridges from different machines. Last but not least, it also enforces traffic policies defined using OpenFlow.

The SDN tutorial - OpenFlow with OpenVSwitch on Oracle Linux, starts from where we left in the "Free Range Routing (FRR) And OpenVSwitch On OracleLinux" post, extending its Lab and provides a practical guide on how to write and set OpenFlow rules on OpenVSwitch.

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In an Infrastructure As Code (IaC) scenario, rather than provision a VM and install a networking dedicated appliance, it is best to provide something without a web-UI but that provides a good configuration API or that sources its settings from something that can be easily managed by automated configuration tools.

In such as scenario it is more convenient to just use one (or more) Linux VM with a very basic installation, having it manage infrastructural networking: these VM can not only manage networking using routing protocol such as RIP, OCSP and even BGP, but also enforce security policies dropping unauthorised traffic.

In this post we see Free Range Routing (FRR) and OpenVSwitch on Oracle Linux in action, setting up a Lab with two virtual machines providing routing sharing routing tables using OCSP: we achieve this by installing Free Range Routing (FRR) - a free and open source Internet routing protocol suite for Linux. The advanced setup shown in this lab also makes use of OpenVSwitch, stacking FRR on top of it.

This dual layer setup enables us to exploit the Software Defined Networking (SDN) features provided by OpenVSwitch, enhancing by adding dynamic routing support, but also providing a compatibility layer with legacy bare metal devices such as "traditional" hardware routers.

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In the "OpenSSL CA tutorial - a full-featured OpenSSL PKI" post we set-up a full featured Public Key Infrastructure with Root and Intermediate Certificate Authorities, Indirect CRL and OCSP Responders. To have a go with that PKI, we also generated an Extended Validation (EV) certificate ("/tmp/foo.crt").

In this post we are using the same PKI we set up in that post, the EV certificate we generated and we also generate a new Organization Validated (OV) certificate: the goal this time is showing how to deal with Indirect CRL generation, CRL validation and OCSP validation.

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OpenSSL is a full featured tool capable not only to generate keys and certificates, but also to provide every facility a PKI must have, such as indirect CRL and OCSP responders: these features, along with certificate's best practices such as the Certification Practice Statement (CPS), publishing CRL Distribution Points URL, OCSP Responders URL, CA Issuers URL, are the topics of the OpenSSL CA tutorial - A full-featured openssl PKI. 

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As we saw in our post on Symmetric And Asymmetric Cryptography, asymmetric key pairs can be used to encrypt and digitally sign documents, but have a huge shortcoming: since they are just keys, they don't provide the metadata necessary to enable people to securely identify their owner. As we saw in the post on GNU Pretty-Good Privacy, GPG addresses this shortcoming by wrapping the key into a container object (the GPG key) that also embeds some metadata about the owner of the key. Of course also the IETF addressed this problem, defining the standard for X.509 certificates (currently X.509v3). X509 Certificates Howto & Public Key Infrastructure Tutorial explores X.509 certificates and how they are trusted by the means of a Public Key Infrastructure.

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Every system administrator daily use SSH to connect to remote systems and perform they daily tasks: the very most of the time these consist into typing statements on the terminal or copying files from and to the remote system, or again running remote commands, but SSH is much more than this: it not only provides additional facilities such as agent  or forwarding, port forwarding and X11 forwarding, but it has also a subsystem that can be exploited to provide SSH secured services such as SFTP.

The goal of the "OpenSSH Tutorial - The Ultimate SSH Guide To Understand It" post is to tell you what historically drove us to SSH, describe the protocol suite in detail and provide a thorough tutorial on using all of these facilities.

SSH is a huge topic: thoroughly explaining both server and client side would require much more than a single post - actually even just explaining server side would deserve several posts. For this reason this post shows only the minimum required settings that are required server side to enable the features that are instead thoroughly described client side. In addition to that, some parts of this post are a little bit redundant, but it was the only way I found to clearly explain how things work from the client perspective and from the server perspective.

This post is based on Red Hat Enterprise Linux 9, but the same concepts apply to the very most of the Linux distributions.

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