From the monthly archives: December 2008

GNS3: How-to save multiple topology configurations for good

By On December 19, 2008 · 4 Comments

GNS3 is an extremely useful tool if you are using Dynamips to emulate Cisco devices. It is a graphical environment in which even a newbie can do complex configuration by clicking and dragging routers, switches, connections into a topology that can be saved.

The problem that occurred to me in the past (and maybe to you also) is the following. Let’s assume that we create a configuration with routers named R0 and R1 and you save the topology config and also the routers config (“copy [...]

Continue Reading →

Cisco 2800 ISR series

By On December 19, 2008 · Leave a Comment

Continue Reading →

Cisco: How to configure simple IP SLA monitor

By On December 16, 2008 · 12 Comments

Before we begin let’s see what is this SLA term, for those of us who are not very familiar with the Service Provider terms. IP Service Level Agreements (SLAs) enable customers to assure new business-critical IP applications, as well as IP services that utilize data, voice, and video, in an IP network. With Cisco IOS IP SLAs, users can verify service guarantees, increase network reliability by validating network performance, pro actively identify network issues assure an easy way to deploy new IP services. Cisco IOS [...]

Continue Reading →

Cisco: Simple configuration of IP multicast dense mode

By On December 15, 2008 · 5 Comments

Until now, I did not meet a network engineer to be really “in love” with multicast. Some are considering challenging, interesting, useful but most of the network engineers (I repeat myself, from the persons that I discussed with) are rather preferring do other topics that multicast. If you are curious about my position in regarding multicast, well I’m somewhere in the middle. I consider it challenging, a topic for the future (like IPv6), I MUST know it, but let’s say that is not my strongest [...]

Continue Reading →

Cisco: BGP path selection for inbound traffic

By On December 10, 2008 · 3 Comments

In some previous post we saw how we can manipulate BGP paths using attributes for outgoing traffic. Today we will see how to use another BGP attribute, but this time for manipulating inbound traffic. First I would like to ask you to have a look into the topology file and also to check the config files (if you have a basic idea about how BGP is configured that you don’t need the config files).

From the [...]

Continue Reading →

Cisco: Traffic manipulation with Policy Based Routing

By On December 5, 2008 · 3 Comments

Cisco Policy Based Routing provides a flexible mechanism for network administrators to customize the operation of the routing table and the flow of traffic within their networks. Policy Based Routing (PBR) offers many advanced features, including selection and forwarding of traffic to discreet Virtual Routing and Forwarding (VRF) instances, as well as Enhanced Tracking of the availability of next-hops. More about PBR you can read here.

Before we start this tutorial please download the topology file [...]

Continue Reading →

Cisco: Very simple NTP configuration

By On December 3, 2008 · 2 Comments

NTP (Network Time Protocol) is usually very simple to configure on Cisco devices. Of course you can reach complex configuration, but since I work in this field I didn’t saw somebody to push the things to extreme in NTP configuration.

NTP is based on server – client relation. It is recommended that in a Cisco network environment, you should use online the client part of the NTP, and to choose some external NTP sever to synchronize with.  This is because using a NTP server (master) [...]

Continue Reading →

Cisco: How to improve BGP table stability with route dampening

By On December 3, 2008 · 4 Comments

One of the issues that can affect BGP table stability is link flapping. Imagine that if a link to a network is flapping very often, BGP process has to remove the route to that network from the BGP table and implicit from the routing table and then we the link is available again to re-introduce the prefix in these tables. All this means some BGP operations that consume CPU and memory of the machine.

A way to improve the BGP table stability is to use [...]

Continue Reading →

Cisco: BGP path selection for outgoing traffic

By On December 1, 2008 · 2 Comments

Before going further on, please download the topology and the initial configuration files and have a close look into them (mostly into topology drawing). Also, this tutorial is addressed to people that know what is BGP and how to do a basic configuration for peering establishing.

For modifying the BGP automate selection of the best path, we have to modify some of BGP attributes from the table below:
Since today we will deal [...]

Continue Reading →