Troubleshooting NTP

Those who have read my article on Non Technical tips on CCIE Troubleshooting and who are following my Technical tips on CCIE Troubleshooting would be wondering why I have chosen to write an article on NTP after writing a post on Troubleshooting MPLS VPN. NTP is trivial as compared to MPLS VPN, so why not the new post on BGP or OSPF? The message I want to send home is that no topic is simple in CCIE. I thought NTP is easy and did not practice it and during Lab, this simple topic caused me to go blank because without practice, there is no strategy and without strategy you don’t know what to do. In this article we will see few scenarios with regards to troubleshooting NTP in a Cisco network. Continue reading

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Troubleshooting MPLS VPN

As I had promised in my post “Non-Technical Tips for CCIE Lab Troubleshooting”, I am back with a series on troubleshooting different networking technologies centering around CCIE Lab. In this post I will be talking about MPLS VPN. For an average person working in Computer Networks, MPLS seems to be a topic which seems to be most scary. Even if their project involves just an MPLS circuit between 2 locations, the word “MPLS” still scares them although there is not much difference between it and a layer 2 circuit. I have received International calls from many of my friends and colleagues who were overwhelmed by MPLS. This could stem from lack of knowledge on MPLS or the way many people teach MPLS. I have seen many guys teaching MPLS by jumping straight to configuration. This teaching method even overwhelmed me, so I tore apart MPLS VPN to understand it better and if you see the concept first and then individual protocols, it might not seem that difficult. In this post, I will not explain MPLS VPN but help develop a strategy to troubleshoot MPLS VPN. It is expected that you know MPLS beforehand to make sense of it or at least have partial knowledge. As I had mentioned in my previous blog about the disadvantages of “Show Run”, so I would be concentrating on using debugs and show commands rather than show run for troubleshooting. Continue reading

Tracing Cables with CDP

Information Technology has become such an important part of our lives that not even a single facet of our life has been left untouched by it. The field is so vast and deep that it is not possible for one person to know everything. Every Specialty requires a specialist and some times a single person is expected to know more than one specialties. There are programmers, networkers, database admins, network and information security officers, voice admins, etc who look into managing their respective domain. There is a segment which is oft ignored and assigned to people who are reluctant on taking the responsibility or to unskilled staff. This segment is cable management. Continue reading

MPLS VPN Torn apart

MPLS is one of the topic where there is too much entry barrier as far as information is concerned. You have to deal with new protocols, different label types, MP BGP, VRFs, etc. on top of the fact that we don’t get exposure to it in our day to day networking (except if you work for an ISP). When I was taught MPLS the first time, it was very difficult for me to visualize (I rely heavily on visualization to understand a topic) the flow as labels had been flying all over the place and pushed and popped and what not. So this is my attempt to explain MPLS VPN by tearing open the packets and showing you what takes place across the network. I will try my best to make it as graphical as possible. Continue reading

Why Traceroute drops packet at Last Hop?

In our work environment we are always surrounded by people who are either smarter than us or act smarter than us. If we are surrounded by people who are smarter than us, the advantage of working with such people is that you will learn a lot from them, this obviously if they are the good ones who happily share knowledge. If they are unwilling to share knowledge, their presence or absence doesn’t make a difference. If we are surrounded by people who just act smart rather than are smart, we must be very careful as the knowledge which they would be sharing might not always be right as they just want to show that they know while they know not. This can be very bad because at the learning stage if you learn all the wrong things, your foundation will be built on wrong information. The best thing anyone who does not know certain thing can do is just say that he doesn’t know so that we can search for the right reason. The best thing about knowledge is that it is no ones property. Whoever desires to acquire knowledge can easily do it. Continue reading

Build your own Cisco Terminal Server with Raspberry Pi

I have been working in Computer networking for more than 8 years now and the biggest fear I still harbor is losing access to a router by misconfiguration. During my first stint with Service Provider networks, losing access to a router or switch would mean running to the Data Centre and taking console to a router and revert the changes and this because we didn’t have console servers in our Data Centre. Our Data centre was just across the NOC so it would take less than a minute to reach the equipments. During my second stint, the Data centre was the largest in India and going to the Data Centre would take minimum of 15 minutes from the NOC. Although we had a management network connecting all networked equipments, this did not help when a router or switch was malfunctioning and the only option left was taking console. My third stint with Service Provider network had no option of running to the router as many of the PoPs were international. Few of the larger PoPs had Terminal Servers but not all had this. A question would run through anyones mind as to why someone would not provision a console server on a remote site? The primary reason is the cost. The second reason is that it does not make business sense to have a console server for a couple of routers. Continue reading

MPLS VPN QoS with GNS3 and Virtualbox

The integration of Virtualbox with GNS3 has driven me crazy as simulations you can do with it are limitless. When QoS over MPLS is concerned, not many websites are available explaining it in simple terms. The vast majority of results you might get on google would refer to Cisco documentations. It gives me chills to refer to Cisco documentations as it is just too vast and the thought of it overwhelms me. So in this blog, we will see how QoS works in an MPLS environment and the various types and options available with it. We will make a vanilla MPLS setup so that we can concentrate more on QoS. Continue reading

QOS with GNS3 and Virtualbox

With the addition of Virtualbox to GNS3, you can do all sorts of simulations (except full switching) involving routers, firewalls, servers (windows or linux), applications, etc. It used to bother me a lot to run a network topology and rely on ping and tftp as test traffic for QOS. Now you do not have to rely on boring traffic to test QOS. You can use actual user traffic and classify and mark it on your routers to give it preferential treatment. You can set bandwidth caps on certain protocols, you can prioritise certain protocols, you can remark certain protocols, etc. The options for QOS testing are limited by your imagination.

In this blog, we will cover basic user traffic like web, ftp and windows sharing and classifying them to mark for QOS treatment. We will rate limit some, prioritise some and remark some on our network and see its effects on the destination end. We can also use the relevant show commands to verify proper operations. Continue reading

Non-Technical Tips for CCIE Lab Troubleshooting

With the introduction of Troubleshooting section in CCIE Lab Routing and Switching, getting the CCIE number has become ever so difficult. I have even come across people who have switched to other CCIEs like Security, Voice, etc because clearing Troubleshooting section was beyond them. The other problem with TS is that it is placed before the Lab exam, so if you think that you will not be able to clear TS Section, you will have absolutely no interest in completing the configuration portion. The disadvantage to this is that you will lose the free attempt to practice configuration section which would be helpful in future attempts.

In this blog I will write about the Non-Technical aspects which might help you in clearing the TS Section. There are several things you must know before you attempt the TS Section, during the preparation for it, before attempting it and during the attempt. These inputs are based on my experience and could differ from people to people. Continue reading

MPLS across Multiple Cities over Internet

Many articles have been written about MPLS VPN amongst different ISPs but not much information is available if there is a global ISP having PoPs across several cities in the world. In this blog, we will look into a way of providing MPLS connectivity to customers present across various cities of the world where you have point of presence. Since, the geographical location of your PoPs are diverse, your PoPs might as well be connected over the Internet. Continue reading