Valley-free routing is a concept that may not be well known but that is relevant to datacenter design. In this post, we’ll valley-free routing based on a leaf and spine topology. There are many posts about leaf and spine topology
Is One Protocol Simpler Than Two?
I’ve been in a lot of interesting discussions the last couple of days on what protocol to use for the underlay when building a VXLAN datacenter network. Do you use an IGP such as OSPF or ISIS or do you
Unnumbered Links In OSPF
This post is going to be a real deep dive! First, I want to send my sincere thanks to the maestro Peter Palúch and the guru Ivan Pepelnjak for helping me research this topic. Ivan wrote a couple of great
OSPF Convergence In a Hub and Spoke Topology
My dear friend Micheline Murphy posted an excellent question on OSPF in a Hub and Spoke topology at the Cisco Learning Network. The scenario is a Hub and Spoke topology with two Hub routers that are ABRs belonging to area
OSPF Design Considerations
Introduction Open Shortest Path First (OSPF) is a link state protocol that has been around for a long time. It is geneally well understood, but design considerations often focus on the maximum number of routers in an area. What other
OSPF – Non Broadcast and Point to Multipoint
Introduction There was a discussion on a forum about the point to multipoint network type in OSPF. What is the purpose of it and why are /32 endpoints advertised? To understand the solution we must first understand the problem. This
Why fast IGP timers aren’t always beneficial
Introduction When tuning your IGP of choice, the first thing people look at is usually the hello and dead interval. This is a flawed logic, it is true that it can help in certain cases but convergence consists of much
Some pointers on OSPF as PE to CE protocol
There was a discussion at the Cisco Learning Network (CLN) about OSPF as PE to CE protocol. I wanted to provide some pointers on using OSPF as PE to CE protocol. RFC 4577 describes how to use OSPF as PE
Why OSPF FA is only set on broadcast networks
A friend of mine asked me about the OSPF forwarding address. The question was why must the network type be broadcast for the FA to be set? Why is not point to point and point to multipoint network type valid?
Tiebreakers with routes from different OSPF processes
This post is inspired by a discussion at Twitter with Ivan Pepelnjak and Nicolas Michel. Nicolas asked what happens when there is the same route from two different OSPF processes. Which one will be selected? Ivan explained how to use