Tag: packet

Packet capture in Cisco IOS

Packet capture on IOSThis will be a brief article but a good one. It will save you some walking time to server room. I have the need to capture traffic on the switch or on the router several times every week. That action needed from me to be physically near the switch and to configure SPAN port so that I can connect to the switch with my machine and capture some packets with wireshark. Okay, I could use RSPAN to get captured packets to the closest switch but this altogether is not good enough. It’s too time consuming for short packets captures in troubleshooting sessions.

Recently in my CCIE study I came across the info that Cisco IOS is able to capture packets on the device itself and on more interfaces in once. You can later export that capture to your PC and analyze it with wireshark.

You can do it like this

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Data Packet – IP Packet – What is this packet story all about?

From the computer networking point of view, a packet is referred to a planned data unit. But certain computer communication links such as point to point communication don’t support data packets. In such cases, data is simply transmitted as an array of bytes or characters etc over the medium. Anyway, transformation of data into packets is a good way to achieve better bitrate of a communication medium in the course of sharing data amongst the users.

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How we open a web page – what is going on behind?

Open a web page, here we will see  how is this happening in the system.  TCP/IP protocol is what makes sending and receiving of data across the internet from some remote server or remote end user. But how data knows how to find us and how we know how to find the IP addresses of the web servers where are the pages saved? Data is not even going on the same way when we send something (a request) to the server, and the server response in shape of data flowing to our computer. Internet is big system that knows in every moment how to find the best route to some device connected somewhere in between all this nodes. But how is this data traveling across the wires, fibers and air? Data is divided in small packets. Every time we send a request to a server, our request first must be divided in smaller packets of the same size and then they are going to DNS – domain name server that will have the information of direction in which direction request must be forwarded. DNS have the knowledge of IP addresses for all URLs that are registered on the internet, and with this database he can translate our request for webpage in the same request but pointed to IP address of the server on which the webpage is stored.

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