Cisco: How to configure simple IP SLA monitor
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 IP SLAs use active monitoring, enabling the measurement of network performance and health.
For the following how-to please have a quick look into the topology. As you can see I have a basic routing topology, imported from another tutorial from FirstDigest, and let’s assume that we want to monitor the line between R1 and TEST-RT. For this we will configure a very simple IP SLA monitor, based on icmp echo packets, which will measure our RTT (Round Trip Time) or latency and provide us with valuable informations. For example in case of VoIP problems we can check the latency and in case of a value bigger than 200 ms (220 ms maximum accepted for the voice service to function properly) we will know from where are the problems generated. Of course IP SLA can have more complex configuration under Cisco IOS (e.g. http or ftp transfer to check if the service provider assure us the bandwidth specified in the contract).
One personal advice from my experience. Even if all the data and information provided by IOS IP SLA monitor can be checked with “show…” commands, I would advice you to get a third party software that can interpret this data for you and draw nice graphs or store them in an archive for you. This kind of software are MRTG, Weathermap, Nagios, RRDtool and others (I put here only the free ones).
Please check the how-to by clicking the image below:
Cisco: Simple configuration of IP multicast dense mode
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 topic in networking.
I think that I can share some of my experience here with you, and maybe discuss a little bit on th multicast subject. And since I do not want to enter more complex multicast configuration from the start I said I should take it slow with the easiest one: multicast dense mode configuration. As you know there is also sparse mode configuration which can be configured in a more complex way, and I will do it in next tutorials. For now I only hope that you know what is multicast and words like PIM, IGMP, dense-mode, sparse-mode does not sound like alien descriptions for you. If you are feeling insecure about this topic, please check this link as you might get very good information about IP multicast.
For this tutorial I have a simple point to point router connection (R1 and R2) with a subnet of 10.0.12.0 /24 in between, and each router has an additional host (R1 has the multicast sender connected and R2 has the multicast reveiver connected). Since I have no possibility to test the IP multicast traffic in this configuration, the explanation above is just to have a picture about the environment. I hope that for the multicast sparse mode I will find a way to generate some multicast traffic, when I will write the tutorial somewhere next weeks.
Please see the tutorial by clicking the image below:
Cisco: Using system banners announcements
Configuring banners on Cisco devices is very easy and it is a study material for CCNA. Even so, I found that not everybody is aware of the importance of the banners or know how banners can be used properly.
There are quite a lot of system banners that can be configured on a Cisco device, but today I will explain only the most used, or let’s say the most that I use, since this is a subjective choice. You will find below the banners name and a short explanation:
- banner motd – add a message-of-the-day (MOTD) banner; usually not so important, but in case of urgent maintenance work can be useful; when someone connects to the router, the MOTD banner appears before the login prompt
- banner exec – display a banner on terminals with an interactive EXEC; after the user successfully logs in to the router, the EXEC banner or incoming banner will be displayed
- banner login – when someone connects to the router, the MOTD banner (if configured) appears first, followed by the login banner and prompts; e.g. it can be useful to display a warning in case that you are not authorized to access the machine
- banner prompt-timeout – it display a message when the user is delaying a login above the definite period of time
If I forgot some very important banner or one that you find extremely useful please remind me to add it here or in another post. Please see below how to configure the system banners that I just described:
Cisco: BGP path selection for inbound traffic
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 table above:
we see that the attributes needed for inbound traffic manipulation are AS-Path and MED. Today we will use AS-Path for traffic manipulation (MED sometime in closer future).
Beside using BGP attributes, there are other ways to manipulate traffic and paths in a BGP environment, but usually this need that the provider will support your actions. As an example to understand, you can do route tagging in your network (for example in MPLS on your CE) and your ISP will apply rules based on different tags (on PE side), but this is out of the scope of this tutorial and will be discussed maybe in another tutorial.
For our test environment, that you see in the topology, we advertise everything into BGP domain, exactly as draw, so there will be no problems of reachability.
Please see the tutorial and explanations below:
