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Blog Posts in May 2021

Video: Cisco SD-WAN Site Design

In the Site Design part of Cisco SD-WAN webinar, David Penaloza described capabilities you can use when designing complex sites, like extending SD-WAN transport between SD-WAN edge nodes, or implementing high availability between them. He also explained how to track an Internet-facing interface and a service beyond its next hop.

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Does Small Packet Forwarding Performance Matter in Data Center Switches?

TL&DR: No.

Here’s another never-ending vi-versus-emacs-type discussion: merchant silicon like Broadcom Trident cannot forward small (64-byte) packets at line rate. Does that matter, or is it yet another stimulating academic talking point and/or red herring used by vendor marketing teams to justify their high prices?

Here’s what I wrote about that topic a few weeks ago:

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Back to Basics: The History of IP Interface Addresses

In the previous blog post in this series, we figured out that you might not need link-layer addresses on point-to-point links. We also started exploring whether you need network-layer addresses on individual interfaces but didn’t get very far. We’ll fix that today and discover the secrets behind IP address-per-interface design.

In the early days of computer networking, there were three common addressing paradigms:

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BGP-Free MPLS Core with Segment Routing

After I created the Segment Routing lab to test the relationship between Node Segment ID (SID) and MPLS labels (and added support for IS-IS, SR-MPLS, and BGP to netsim-tools), I was just a minor step away from testing BGP-free core with SR-MPLS.

I added two nodes to my lab setup, this time using IOSv as those nodes need nothing more than EBGP support (and IOSv is tiny compared to IOS XE on CSR):

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Response: There's No Recipe for Success

Minh Ha left a lengthy comment to my There’s No Recipe for Success blog post, adding an interesting perspective of someone who had to work really hard to overcome coming from a third-world country.


Ivan, I happened to read “Deep Work: Rules for Focused Success in a Distracted World” recently so I can attest that it does provide some valuable advices on how to do things well. Some of the overarching themes are stay focused and cut off unnecessary noise/drain the shallow. The author also suggests removing your social media account if you can’t see how it add values to your work/business, as social media can create attention disorder, seen in many young kids these days.

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Worth Reading: When Stretching Layer Two, Separate Your Fate

Ethan Banks wrote the best one-line description of the crazy stuff we have to deal with in his When Stretching Layer Two, Separate Your Fate blog post:

No application should be tightly coupled to an IP address. This common issue should really be solved by application architects rebuilding the app properly instead of continuing like it’s 1999 while screaming YOLO.

Not that his (or my) take on indisputable facts would change anything… At least we can still enjoy a good rant ;)

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Back to Basics: Do We Need Interface Addresses?

In the world of ubiquitous Ethernet and IP, it’s common to think that one needs addresses in packet headers in every layer of the protocol stack. We have MAC addresses, IP addresses, and TCP/UDP port numbers… and low-level addresses are assigned to individual interfaces, not nodes.

Turns out that’s just one option… and not exactly the best one in many scenarios. You could have interfaces with no addresses, and you could have addresses associated with nodes, not interfaces.

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Segment Routing Segment IDs and MPLS Labels

In one of my introductory Segment Routing videos, I made claims along the lines of “Segment Routing totally simplifies the MPLS control plane, replacing LDP and local labels allocated to various prefixes with globally managed labels advertised in IGP

It took two years for someone to realize the stupidity over-simplification of what I described. Matjaž Strauss sent me this kind summary of my errors:

You’re effectively claiming that SRGB has to be the same across all devices in the network. That’s not true; routers advertise SIDs and must configure label swap operations in case SRGBs don’t match.

Wait, what? What is SRGB and why could it be different across devices in the same network? Also, trust IETF to take a simple idea and complicate it to support vendor whims.

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Feedback: Microsoft Azure Networking

Azure and AWS have decent documentation (I always found it relatively easy to figure out what they’re doing), but what they implemented is sometimes so far away from what we’re used to that it’s hard to bridge the gap. Here’s how Olle Wilhelmsson solved that challenge:

I would just like to send a huge thank you, I’ve been a fan of your appearances on tech field day as a voice of reason, and different podcasts all around. Happy to finally be able to contribute and purchase an IPspace subscription, and was not disappointed.

This series on Azure networking was fantastic, it’s been frustrating to find any kind of good material on this topic. Even if Microsofts documentation is generally good, they really don’t have any resources to compare it to “regular” networking in physical equipment. So just a huge thank you, this has definitely saved me countless hours of reading and googling questions!

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RFC 7868: The Definitive EIGRP Guide

Seventeen years after I started working on my EIGRP book, the reverse engineering days were over: RFC 7868 is the definitive guide to modern EIGRP (I’m not familiar with at least half of the concepts mentioned in it).

Just in case you’re interested in a bit of historical trivia:

  • My EIGRP deciphering history started a few years before the book was published. In mid-1990s I was asked (as an external trainer) to create an EIGRP course for Cisco EMEA Training.
  • I’ve never seen any internal EIGRP documentation or code – everything I knew about EIGRP I’ve learned from trying out crazy stuff and deciphering debugging messages.
  • Two of the RFC authors (Russ White and Don Slice) were the technical reviewers for my EIGRP book. Russ copiously rewrote my pidgin English into something understandable – if you like reading my blog posts today, you should (also) thank Russ.
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