gurfin RiveransRafting

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 yeet

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.

Big Gaming Protocol The big bad Border Gateway Protocol (BGP) is, unlike the OSPF, EIGRP and ISIS, an eBGP designed to connect together large scale networks. Because BGP is built for scale, it is tuned to be a bit more stable than the IGPs. For example it does not allow for dynamic neighbor discovery, but rather each neighbor must be explicitly specified. The BGP hold timers are also a lot more generous than the IGP timers, with the default being 3 minutes.

Building an IaC BIND9 DNS deployment on kubernetes For some time now I have been displeased with my DNS server setup. Previously I have had a single Pi-hole instance running on a Raspberry Pi at one of my sites. This means that private DNS resolution, for the entire network, was dependent on a single site and a single compute node. This Single Point of Failure (SPoF) is not something i was to happy with, and I did not want to point all my client networks to a singular Raspberry Pi.

OSPF version 3 To support IPv6 routing, OSPF version 3 (OSPFv3) was created. It has support for both IPv4 and IPv6, but is not backwards compatible with the version 2 standard. In fact, the protocol is designed to be independent on the address family type. The communication between routers is based entirely on IPv6 though, using link-local addresses. There is also support for multiple instances within a network, which allows you to configure which routers are able to form adjacencies.

Path selection for good old OSPF Path selection is based on the Shortest Path Tree (SPT) found using Dijkstra’s Shortest Path First (SPF) algorithm. Generally OSPF prefers intra-area routes, inter-area routes and external routes, ordered from most to least preferred. If two paths exists for a given route, within the same area, then the one with the lost total metric is injected into the RIB. If two routes have equal total metrics, then both are generally injected into the RIB.

Open Shortest Path First (OSPF) 🗺️ Areas are a way to divide an OSPF domain into smaller, logical chunks, which allows for less resources to be used by the OSPF process. Each interface on an OSPF router can only be member of a single area, however, an OSPF router can have interfaces in multiple areas, thus becoming an Area Border Router (ABR). A unique LSDB will be created for each area that a router is a member of.

The basics of routing When traffic needs to traverse different networks it must be routed. This is usually done in a router (hence the name). In order for a router to send a packet correctly, it must know which interface to route the packet out of, and in the case of non point-to-point links it also needs to know which L2 device to send the frame to. In order to do this the router will keep a table of all the currently active routes which will then be used to program the ASICs with.