Blog – routingloop.net

EIGRP in Clos Topologies

Link state protocols or BGP are typically used for underlay routing in data center fabrics, deployment of these protocols is Clos (aka spine and leaf) topologies are well documented. I decided to experiment with EIGRP to get a better understanding of its operation in such topologies. Although I don’t expect to ever see a production

Are We Spending Too Much on the Network?

26NovemberStevenRouting

Are We Spending Too Much on the Network? It’s a reasonable question. Many textbooks about networking have info about aggregating routing information, optimizing link state designs for more optimal flooding and shorter SPF runs, and many other techniques that were mandatory when router CPU and memory were a rarity. Moore’s Law continued to deliver and

A Thing About EIGRP Summaries

2OctoberStevenHome Lab, Routing

IP route summarization, sometimes called aggregation, allows us to suppress the advertisement of multiple longer prefixes into a shorter prefix that encompasses a range of more specific routes. There are plenty of excellent guides on summarization, so I’ll spare those details here and jump straight into some EIGRP specific things about summaries. Demo Network For

Clear arp-cache vs clear ip arp

20SeptemberStevenHome Lab, Routing

Cisco IOS CLI provides two different commands that seem the same on the surface but have a slightly different outcome on the wire. Based on the title you probably guessed that it’s clear arp-cache vs clear ip arp. To see the difference, I connected two routers on network 10.0.0.0/30 with a SPAN enabled switch in

TCP CUBIC vs BBR Pt. 1

1AugustStevenHome Lab

TCP congestion control algorithms have a tough problem to solve. They need to estimate the available capacity of a network path without any knowledge of network. Remember that TCP runs in the end hosts. It’s important to estimate the network capacity to achieve the maximum throughput for a single flow while sharing network resources with

Don’t Have a Bad Day

31MarchStevenHome Lab, Routing

Anycast RP with Multicast Source Discovery Protocol (MSDP) is a great way to provide fault tolerance to your multicast network. Configure another router with the RP address, bang out a few msdp commands on the RP routers and you’re all set for a basic anycast RP design. It’s important to not get tunnel vision and

EIGRP Metric Calculation

27MarchStevenHome Lab, Routing

If you’ve worked with or studied EIGRP, you’ve probably seen that scary formula with the K values that EIGRP uses to calculate routing metrics. It turns out that if you’re using the default K values so that only bandwidth and delay are being considered, the math involved isn’t that bad. In this article we’ll explore

IPv6 Next Hop

16MarchStevenHome Lab, IPv6, Routing

Over the last two weeks I’ve been focusing on strengthening my knowledge of IPv6 and it got me thinking about usage of link local addresses as the next hop for routing. It became apparent that this difference from IPv4 makes it possible to have equal cost next hops via the same output interface and for

IPv4 Fragmentation

2MarchStevenHome Lab, Routing

One of the attributes that helped IPv4 stand the test of time is the ability to slice and dice big datagrams into multiple smaller ones on the fly. This provides tremendous flexibility for different data links and their maximum packet size, reduced MTUs inside of tunnels, and the like. The process of chopping up IP

Exploring CEF

25FebruaryStevenRouting

There are a few fundamental actions that a router must perform to take a packet coming in one interface and forward it out of another. The router must perform lookups to determine the exit interface and next hop information, it must rewrite the data link layer header and trailer for the egress link, and if