Configuring Generic Routing Encapsulation (GRE) tunnels on Cisco IOS

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Overview

Generic routing encapsulation (GRE) is a tunneling protocol which was initially developed by Cisco, and later it has been adopted as an industry standard in RFC 2784. GRE allows the encapsulation of a wide variety of network layer protocols inside virtual point-to-point links. This means that the original packet is encapsulated inside a GRE header and a new IP header containing the source and the destination of the tunnel endpoints. The GRE protocol does not provide any security for the data being transported so if encryption is needed GRE must be used in conjunction with IPsec protocol. Some of the reasons for using GRE are the need to transport multicast traffic, or to provide workarounds for networks with limited hops. In this article we will demonstrate how two networks which do not have reachability can be connected through an GRE tunnel.

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Configuring Policy Based Routing on Cisco ASA

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Overview

Normally when a routing device receives a packet it decides where to forward it based on the destination address of the packet. Policy Based Routing (PBR) is a mechanism which allows you forward packets based on policies manually defined by network administrators. A good use case for PBR is when a company which has multiple outside connections to different ISPs needs to control how traffic can be distributed across these connections. Compared to traditional routing PBR allows you to implement routing policies based on different criterias like source or destination address, source or destination port, protocol, size of the packet, packet classification and so on. Cisco introduced this feature on Cisco ASA beginning with version 9.4(1). Let’s dive into the PBR configuration.

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Configuring and deploying Cisco IOS certificate server

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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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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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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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