Configuring BGP - Advertising default route to neighbors - default originate

This post is dedicated to my good friend / colleague Mr. Rage :) 

In this blogtorial we will explore one of the methods by which we can advertise a default route to BGP neighbors. One of my colleagues last week asked "would we loose the BGP default route advertisement if the advertising neighbor lost the default route in its own RIB" and honestly I wasn't sure. And I hate being unsure of "something" network related. So I did what any curious person would do, I lab'd it up and it turns out that default route advertisement is not lost when you loose the default route in the routing table, although you can certainly configure it as such.

Here is a simple topology to get started. 

TCP SACK Demystified

In this blogtorial, we will briefly explore TCP SACK (Selective Acknowledgement) option and the benefits of using TCP Selective Acknowledgement. TCP SACK is negotiated in the initial 3-way TCP handshake and both parties must agree to use this option or TCP SACK will not be permitted.

Let's walk through an example and observe what happens when SACK is not enabled.