All Entries in the "Cisco-technology" Category

Cisco: Quick IOS check in 4 simple steps

This post is rather for the beginners in Cisco’s world than for advance professionals, but still I encounter situation when IOS image was corrupted even if it was uploaded to the device by a network guru. Why? It’s quite simple! Because you can be the master of the Cisco networking,  but still sometime you cannot control the device behavior or the transport of the packets to destination.

The problems is that in case of a corrupted IOS image being uploaded on a Cisco device, and having that device reloaded you can run into situation when it will not boot up anymore. When the device is in front of you, or on your desk, there is not a problem, because you can troubleshoot, find the issue (e.g wrong or corrupted IOS image) and solve it! But, what if your device is at 5000 km distance, it is 3:00 AM and you have no professional help on that location?! That’s one ugly situation and the reason for which I always insist to verify the IOS image after it is uploaded and ready to go into production.

For those of you who are dealing with this stuff everyday, this post may seem like a joke, but I bet that there are out there IT’s which never check this stuff or they are beginners and don’t know how to do it. It’s more simple that you may think it is, make you spend about 4-5 minutes for a full check, but can spare you for bigger problems in the future.

So, what are the 4 steps:
1. Check what Cisco device you have (to know what IOS image you need)
2. Check what IOS image Cisco device has (to know what IOS release to download)
3. Verify the IOS image
4. Check the results of your verification
As simplest as it can get.

Please check the tutorial by clicking the image below:

For those who cannot see a Flash movie, please read this text file, that consist of the command you should perform for IOS checking.

Popularity: 4% [?]

Cisco: Layer 1 link failure detection

It has been a while since I didn’t post anything here, but it was holidays and I used that time to relax and rest after a year of work. Following this idea I wish you all “Happy New Year” and all the best in 2009.

Today I planned to write about something easy to implement (just to get in shape), but ignored by some network engineer. For me, Layer 1 issues are very annoying, and here I’m talking mostly about the cases when everything look perfect on your side, cable is plugged in, you have green light for the link, but nothing is working.

Luckily some smart engineers think to develop and implement a feature called Unidirectional Link Detection (UDLD). UDLD is used to detect when the send channel (Tx) of a cable is down, but not the receive channel (Rx) and vice versa. This situation typically can occur in a fiber optic cable when there is a break on one side of the cable run or in copper cable when Rx or Tx pair is broken. When UDLD detects this situation the interface is brought down to prevent spanning-tree loops and black holes due to  unidirectional links.Remember, UDLD is a Layer 2 protocol that with Layer 1 mechanisms to determine the physical status of a link.

Please have a look below for a configuration example:

Popularity: 3% [?]

Cisco: Multilink PPP over Frame Relay (MLPoFR)

In this tutorial I propose to show something that is not very used these days, or at least not every day, but which can be tricky if you don’t know how to approach this type of configuration. To understand this, I assume that you know the basics about PPP, FR and Multilink. I will make a short summary here but I will not go into details:

PPP or Point-to-Point protocol is used to establish direct connection between two network points. It can provide authentication, encryption privacy and compression.
FR or Frame-Relay is a telecommunication service used mostly on the WAN side towards your provider or carrier and it relay on frames for data transmission.
Multilink is used for bundle together 2 or more channels / circuits for communication improvement.

Here we will use these 3 technology to create something called MLPoFR. For security we will use authentication. Please download here the topology. Please be aware that in the topology you cannot see actually 2 links there (it a limitation of GNS3), but trust me the links are there. To be more convenient and quick the R1 of the topology is preconfigured.

Please see the tutorial below:

Popularity: 2% [?]