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In the beginning, God created IPv4 When the internet was first created, large public IPv4 address blocks were handed out and assigned to organizations. When the usage of the internet grew it became quite apparent that the available IPv4 address space would not be enough. One of the most implemented solutions to this problem is Network Address Translation (NAT), which allows Layer 3 capable devices to rewrite source and/or destination addresses.

This post will be covering some useful, but less heavy technologies, namely NTP and FHRP. These are essential to building a resilient and well functioning network. It’s funny, every time I work with NTP I am reminded of when I took a certain exam. During one of the labs there was a need for configuring NTP on a router - simple enough, I though. I spent about 40% of the entire allotted exam time on trying to get NTP to synchronize - turns out, that everything was correctly configured and NTP was just slow… 🤦‍♂️

Quality of Service (QoS) is a technology that you hope you never need to use, but when you do, it’s really handy! The core principal of QoS is to allow us to affect the network resource allocation based on the given service and it’s requirements. QoS is a technology that only becomes relevant when you have a network that is strained in one or more of the following ways: Insufficient bandwidth Jitter or latency Packet loss In situations where you are not experiencing the aforementioned issues, QoS will not bring any benefit to your network.

Ever wanted to try being your own ISP? Ever wanted to setup a transit AS while hosting some services on IP-addresses you own? Enter “dn42” (https://dn42.eu/), where you are able to build an overlay network of software or hardware based routers and do BGP peering with hundreds of other AS:s. For a couple of months now I have been itching to setup a dn42 network to learn some more about software based routing and networking in the cloud.

I have a special appreciation for the multicast technology. Back when I used to work in first line support for a Swedish service provider of IPTV, I was always intrigued by the efficiency of using multicast to deliver the TV to peoples homes. Using multicast drastically reduced the bandwidth requirements for the central streaming sources that were used to send out the TV broadcasts onto the fiber networks. Now, in recent years service providers have moved away from this and into using unicast streaming in stead.

A project I have recently undertaken requires me to use linux based routing processes to communicate with other peers. The software I have chosen to run is bird2, which allows me to establish adjacencies with and BGP peer, Cisco or other. I have noticed however, that I find myself google:ing the same commands over and over again. So I though I would collect all the commands I have found to be useful in a blog post, that I myself can refer back to.

Summer and winter time adjustments is something that causes quite the headache when you want all your devices to have an accurate clock. This is especially important when you are going to review logs. I will therefore share a short snippet of config which can be used to set the clock of a Cisco IOS-XE device to correctly adapt to the summer/winter time. clock timezone SWEDEN 1 0 clock summer-time SUMMERTIME recurring last Sun Mar 3:00 last Sun Oct 3:00 In order to also display log entries with the correct timestamp you need to add the following command:

I have been doing this blog now for the past year, admittedly with varying intervals between posts. Reflecting on everything I have written is becomes apparent how my interest and focus has wandered around during the last year. Everything from traditional routing on Cisco platforms and MPLS, to building CI/CD pipelines and deploying applications to the cloud. There are a few posts that I feel have been especially important this past year.

The fiber guide It’s quite common for network engineers not to be as familiar with the hardware side of networking. One of the most common hardware questions I get is about optical network links, something that has become the new standard for network interconnects. So I figured I would do a writeup on the optics topic. Back to basics The goal of a data transfer is to communicate some type of data across distance.

BGP Path selection One of the most essential parts of BGP is its path selection algorithm. It dictates how BGP is to select which paths to promote to the RIB. Using the different Path attributes you can affect how routing of your prefixes is done within your network, in your peers network and even on the internet. The path selection is done in a ascending order, where the first unequal attribute will be the determinator of which path is selected.