Blog – routingloop.net

BGP Graceful Shutdown

BGP Graceful Shutdown is a feature and technique that we can use to minimize traffic loss when administratively disabling a BGP peering session. Graceful shutdown utilizes a well-known community value that was standardized in RFC 8326. We can use the graceful shutdown feature to lower the local preference within the local autonomous system and signal

Remote Triggered Black Hole

1MarchStevenHome Lab, Routing

Remote Triggered Black Hole (RTBH) is a tool we can use to drop unwanted traffic in BGP networks using the forwarding plane. It’s called a remote trigger because once we have the base configuration on all our routers, we can initiate the black hole by making changes on just the “trigger” router. In this article,

Link State Microloops

9NovemberStevenHome Lab, Microloops, Routing

Routingloop.net finally lives up to its name! In this article, I touch on how microloops happen and display how I was able to create and observe a live microloop. What is a microloop anyways? A microloop is a temporary forwarding loop that can occur during network convergence, typically with link state protocols. Why link state?

IS-IS LSP Authentication

29SeptemberStevenHome Lab, Routing

I learned something today that now seems obvious. IS-IS LSP Authentication only impacts the trust of the Link State Packet itself, not IS-IS neighbor maintenance. Neighbor adjacency authentication is a separate function in IS-IS. Neighbors will still form if LSP authentication is mismatched but the LSP content will not be published to the Link State

OSPF v2 LSDB Illustrated

27SeptemberStevenHome Lab, Routing

In this lab exercise, I am going to attempt to draw a diagram of the network based on the OSPF Link State Database (LSDB) using the virtualized network shown below. The diagram will be based on R1’s view of the network. R1’s OSPF Router ID (RID) is 1.1.1.1. Let’s start by examining R1s LSDB at

A World Without Window Scaling

24AugustStevenHome Lab

In the world of modern TCP, window scale multipliers are a commodity often ignored until it’s not there. The window is the number of bytes that the receiving TCP is prepared to receive. RFC 793 states that the window field is 16 bits. With 16 bits, the receiving TCP can indicate that it is willing

EIGRP in Clos Topologies

1DecemberStevenHome Lab, Routing

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