Understand MTU and MRU – The Full Story

MTU or Maximum transmission unit is a topic that pops up every once in a while in different discussions. Although it’s a simple concept, it causes a lot of confusion specially for those who are new to the field. MTU typically becomes an issue of concern during network changes, like adding new vendors equipment or upgrading to a new software. One reason for that is the difference in  implementations used by different vendors or even between different OS versions or equipment  from the same vendor. Here is an example for such confusion  MTU and ping size confusion. On the other …

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Troubleshoot#1: Correlation vs Causation

Network problems can be as simple as follows: Ping neighbor. 100% packet loss. Check network interface, it’s down. Change SFP and you are done, problem solved   But they can also be complex; really complex .. In the past few years, I have had the unplanned privilege to see some of the shi**iest networking problems on earth. Not because I am an unlucky bastard but simply because I am in the position that if it reaches me, then it’s fairly complex. Dealing with such scenarios have taught me some good lessons that are not necessarily limited to networking or IT. …

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text2pcap – How to convert ASCII packet dumps to .pcap files?

Nothing in my experince is better at telling the real story than a packet capture. They tell exactly what is really going on and whether the configuration or changes are working  as expected or not. Sometimes an engineer needs to look at packet captures taken from devices that don’t generate .pcap files directly. Although with some experince and familarity, one can visually inspect some packets for certain pieces of informaiton but after all this is what computers are made for. You are probably familiar with text2pcap but in case you aren’t, It is a command line tool that comes pre-installed …

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PPPoE MTU Explained

PPPoE MTU is a buzz word that many people ask about even if they don’t have anything to do with network engineering. Just being a broadband subscriber with a PPPoE circuit is enough to get introduced to the concept. In this post I will be explaining how PPPoE MTU is calculated and what is the default value. Therefore I would expect the reader to be familiar with what MTU is and with What PPPoE is. PPPoE MTU: PPPoE MTU defines the maximum number of bytes that a PPPoE payload can have. This typically starts from IP layer in most cases. …

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What is MTU?

MTU stands for Maximum transmission unit, which is the maximum packet length that can be sent on an egress interface toward a destination. MTU is an attribute of the egress interface and is typcially considered over a full path from the source to destination. MTU size differes from one media to another and is often a source of issues when configured incorrectly in the network. The following posts will give deep understanding for What is MTU and how you can manipulate it and set it to the correct value. Understanding MTU and MRU .. The full story The post starts …

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Making sense of Broadband networks – VLAN Model

In the previous post we discussed the major considerations of a broadband network architecture. Now I want to discuss each of those points one by one adding some details. I will do this quick and might not be able to provide illustrations or configuration examples all the time due to time limits, so if anything is not so clear please let me know and I can reiterate this. Qouting from previous post, I was mentioing that a provider has to make a choice between two major VLAN models or combine both: “Which VLAN model? Customer VLAN (know as C-VLAN) or …

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