Category: WAN

After I completed the LAN-over-RS-232 project, it was obvious (well, not in retrospect) that the solution to every problem must be Z80 computers connected with some crazy RS-232 wiring. A few years later we had to write an application to support rally races. Guess what the solution was ;)

Summer is a great time to do odd jobs that you always wanted to do but never found time for. One of mine: document the crazy stuff I’ve been doing decades ago. Starting point: how I got into networking in 1980s.

One of my readers sent me a lengthy email asking my opinion about his ideas for new data center design (yep, I pointed out there’s a service for that while replying to his email ;). He started with:

I have to design a DR solution for a large enterprise. They have two data centers connected via Fabric Path.

There’s a red flag right there…

Mark Baker left this comment on my Stretched Firewalls across Layer-3 DCI blog post:

Strange how inter-DC clustering failure is considered a certainty in this blog.

Call it experience or exposure to a larger dataset. Anything you build will eventually fail; just because you haven’t experienced the failure yet doesn’t mean that the system will never fail but only that you were lucky so far.

One of my readers read the Ars Technica article on ads communicating with other devices via ultrasound and wondered whether something similar could be done for IP.

Not surprisingly, someone already did it. A quick google search found this tutorial which explains how to run IP stack over Gnuradio (at speeds that were last experienced with dial-up modems 30 years ago).

I got this question from one of my readers (and based on these comments he’s not the only one facing this challenge):

I was wondering if you can do a blog post on Cisco's new ASA 5585-X clustering. My company recently purchased a few of these with the intent to run their cross data center active/active firewalls but found out we cannot do this without OTV or a layer 2 DCI.

A while ago I expressed my opinion about these ideas, but it seems some people still don’t get it. However, a picture is worth a thousand words, so maybe this will work:

You might remember the great idea David Barroso had last autumn – turn an Arista switch into an Internet edge router (SDN Internet Router – SIR). In the meantime, he implemented that solution in production environment serving high-speed links at multiple Internet exchange points. It was obviously time for another podcast on the same topic.

Another week, another ExpertExpress session, as is often the case focusing on two data centers with stretched VLANs spanning both of them. However, this one was particularly irksome, as the customer ran a firewall cluster stretched across two locations.

I gave the customer engineers my usual recommendations:

When I wrote my stretched VSAN post, I thought VSAN uses asynchronous replication across WAN. Duncan Epping quickly pointed out that it uses synchronous replication, and I fixed the blog post.

The “What about latency?” question immediately arose somewhere in my subconscious, but before I could add that thought to the blog post, Anders Henke wrote a lengthy comment that totally captured what I was thinking, so I’m including it in its entirety:

When I asked “Are there any truly QoS-aware routing protocols out there?” in one of my SD-WAN posts, Marcelo Spohn from ADARA Networks quickly pointed out that they have one – Dynamic Link-State Routing Protocol.

He also claimed that DLSP has no scalability concerns – more than enough reasons to schedule an online chat, resulting in Episode 40 of Software Gone Wild. We didn’t go too deep this time, but you should get a nice overview of what DLSP is and how it works.

::: jump-link Enjoy the podcast :::

One of my readers recently pointed me to a blog post written by Andrew Lerner from Gartner describing the drawbacks of stretched VLANs.

TL&DR: He’s saying more-or-less the same things I’ve been preaching for years. Now I can put Blessed by Gartner logo on my blog posts ;), and you can use the report to sway your CIO.

My Business Case for SD-WAN blog post received numerous comments pointing out the potential pitfalls of hybrid WAN, including reduced security, unreliable Internet services and denial-of-service attacks.

While all those comments are perfectly valid, I still think hybrid WAN (whether implemented with traditional technologies or SD-WAN products) makes perfect sense.

One of my readers sent me an interesting reliability design question. It all started with a catastrophic WAN failure:

Once a particular volume of encrypted traffic was reached the data center WAN edge router crashed, and then the backup router took over, which also crashed. The traffic then failed over to the second DC, and you can guess what happened then...

Obviously they’re now trying to redesign the network to avoid such failures.

Ethan Banks recently wrote a nice blog post detailing the benefits and drawbacks of traditional routing protocols and comparing them with their SD-WAN counterparts.

While I agree with everything he wrote, the comparison between the two isn’t exactly fair – it’s a bit like trying to cut the cheese with a chainsaw and complaining about the resulting waste.

An anonymous commenter wrote this comment to my initial SD-WAN post:

I can still hardly imagine the business case behind SD-WAN. Any thoughts?

This question is really easy to answer. There’s a huge business case that SD-WAN products are aiming to solve: replacing traditional MPLS/VPN networks with encrypted transport over public Internet. However…