Configuring and deploying Cisco IOS certificate server


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cisco

Overview

A Certificate Authority is a trusted entity is that issues digital certificates to devices which need secure communication and plays an important part in the public key infrastructure (PKI). There are several CA implementations provided by third-party CA vendors like Microsoft or the open source OpenSSL implementation but in this article we will focus on configuring the internal Certificate Authority server which is available on Cisco IOS. We will also discuss about the certificate enrollment process with a CA and how these digital certificates can be used for authentication purposes. This feature has been introduced in Cisco IOS version 12.3(4)T and it’s available only on Cisco IOS images with the security feature set.

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Configuring Cisco ASA active standby failover


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cisco

Overview

In modern datacenters one of the most important things that needs to be addressed is uptime. Cisco ASA offers high availability mechanisms like failover in order to provide network uptime and redundancy. In order to configure failover we need two identical ASA devices connected to each other through a dedicated failover link and, optionally, a stateful failover link. There are two different failover modes that are supported on the ASA platform: active/standby and active/active. In this article we will focus only on configuring active/standby failover. In an active/standby failover setup only one unit called the active unit is passing traffic. The standby unit is used as a backup of the active unit and only accepts management connections (all transit traffic is dropped). When the active unit fails, it changes to the standby state while the standby unit changes to the active state.

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Configuring private vlans on Cisco switches


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cisco

Overview

Private VLANs are used to provide layer 2 isolation between members of the same broadcast domain. Private VLANs are documented in RFC 5517. In a standard VLAN environment traffic between members of the same VLAN can flow without restrictions. We can think of private VLANs like a segmentation of a normal VLAN in multiple subdomains. This feature is available only on layer 3 Catalyst 3560s and higher switches. Private VLANs can be used to address two issues found in service provider networks. First using normal VLANs an ISP must assign one VLAN per customer and thus a scalability problem would arise if the ISP needs to support more than 4094 clients which is the maximum number of supported VLANs by a device. Secondly when using IP routing each VLAN requires a separate subnet, which can lead to IP address management problems by wasting unused IP addresses.

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How to configure Port Address Translation (PAT) on Cisco routers


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cisco

Overview

Port Address Translation (PAT), is an extension to the well known Network Address Translation (NAT) protocol that allows multiple devices on a local area network (LAN) to access Internet resources using a single public IP address. NAT is defined in RFC 1631 and the main purpose of using it was to slow the depletion of public IP address space. A practical use of PAT is for example when an ISP allocates a public IP address for an organization which has many devices which need Internet access. PAT uses private IP address classes defined in RFC 1918 for all inside devices and also uses port numbers to identify the connection. When an internal host wants to communicate with the outside it sends a datagram with its private source address and a random port. The NAT router will then rewrite the source address and port with its public IP and sends the datagram to the requested resource. The response will come back to this same public address and port combination (called a socket) and can be translated back again.

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Understanding file permissions and ownership on Linux


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bash

Overview

The Linux filesystem is based on a hierarchical directory structure where the root mount point is defined by the ‘/’ symbol. In fact everything is a collection of files (files, directories, partitions, pipes, sockets, and hardware devices). Directories are used as containers that list other files. Most Linux distributions follow the Filesystem Hierarchy Standard (FHS) for organizing the filesystem structure. Permissions are used to control who can read, write and execute the contents of a file, and ownership indicates to which username and group a file belongs. If you are working as a system administrator, assigning incorrect permissions or ownership can have serious consequences in terms of security. In this article I will explain the theory and show you how to manipulate them using some practical examples.

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