Category: WAN

Video: End-to-End Latency Is Not Zero

After the “shocking” revelation that a network can never be totally reliable, I addressed another widespread lack of common sense: due to laws of physics, the client-server latency is never zero (and never even close to what a developer gets from the laptop’s loopback interface).

You need Free ipSpace.net Subscription to watch the video and the Standard ipSpace.net Subscription to register for upcoming live sessions.
add comment

Connecting Your Legacy WAN to Cloud is Harder than You Think

Unless you’re working for a cloud-only startup, you’ll always have to connect applications running in a public cloud with existing systems or databases running in a more traditional environment, or connect your users to public cloud workloads.

Public cloud providers love stable and robust solutions, and they took the same approach when implementing their legacy connectivity solutions: you could use routed Ethernet connections or IPsec VPN, and run BGP across them, turning the problem into a well-understood routing problem.

read more see 1 comments

Public Cloud Cannot Change the Laws of Physics

Listening to public cloud evangelists and marketing departments of vendors selling over-the-cloud networking solutions or multi-cloud orchestration systems, you could start to believe that migrating your workload to a public cloud would solve all your problems… and if you’re gullible enough to listen to them, you’ll get the results you deserve.

Unfortunately, nothing can change the fundamental laws of physics, networking, or application architectures:

read more add comment

Figure Out What Problem You’re Trying to Solve

A long while ago I got into an hilarious Tweetfest (note to self: don’t… not that I would ever listen) starting with:

Which feature and which Cisco router for layer2 extension over internet 100Mbps with 1500 Bytes MTU

The knee-jerk reaction was obvious: OMG, not again. The ugly ghost of BRouters (or is it RBridges or WAN Extenders?) has awoken. The best reply in this category was definitely:

I cannot fathom the conversation where this was a legitimate design option. May the odds forever be in your favor.

A dozen “this is a dumpster fire” tweets later the problem was rephrased as:

read more add comment

You Don't Need IP Renumbering for Disaster Recovery

This is a common objection I get when trying to persuade network architects they don’t need stretched VLANs (and IP subnets) to implement data center disaster recovery:

Changing IP addresses when activating DR is hard. You’d have to weigh the manageability of stretching L2 and protecting it, with the added complexity of breaking the two sites into separate domains [and subnets]. We all have apps with hardcoded IP’s, outdated IPAM’s, Firewall rules that need updating, etc.

Let’s get one thing straight: when you’re doing disaster recovery there are no live subnets, IP addresses or anything else along those lines. The disaster has struck, and your data center infrastructure is gone.

read more see 1 comments

Disaster Recovery and Failure Domains

One of the responses to my Disaster Recovery Faking blog post focused on failure domains:

What is the difference between supporting L2 stretched between two pods in your DC (which everyone does for seamless vMotion), and having a 30ms link between these two pods because they happen to be in different buildings?

I hope you agree that a single broadcast domain is a single failure domain. If not, let agree to disagree and move on - my life is too short to argue about obvious stuff.

read more add comment

The EVPN Dilemma

I got an interesting set of questions from a networking engineer who got stuck with the infamous “let’s push the **** down the stack” challenge:

So, I am a rather green network engineer trying to solve the typical layer two stretch problem.

I could start the usual “friends don’t let friends stretch layer-2” or “your business doesn’t need that” windmill fight, but let’s focus on how the vendors are trying to sell him the “perfect” solution:

read more see 13 comments

Stretched Layer-2 Subnets in Azure

Last Thursday morning I found this gem in my Twitter feed (courtesy of Stefan de Kooter)

Greg Cusanza in #BRK3192 just announced #Azure Extended Network, for stretching Layer 2 subnets into Azure!

As I know a little bit about how networking works within Azure, and I’ve seen something very similar a few times in the past, I was able to figure out what’s really going on behind the scenes in a few seconds… and got reminded of an old Russian joke I found somewhere on Quora:

read more see 3 comments

Impact of Controller Failures in Software-Defined Networks

Christoph Jaggi sent me this observation during one of our SD-WAN discussions:

The centralized controller is another shortcoming of SD-WAN that hasn’t been really addressed yet. In a global WAN it can and does happen that a region might be cut off due to a cut cable or an attack. Without connection to the central SD-WAN controller the part that is cut off cannot even communicate within itself as there is no control plane…

A controller (or management/provisioning) system is obviously the central point of failure in any network, but we have to go beyond that and ask a simple question: “What happens when the controller cluster fails and/or when nodes lose connectivity to the controller?”

read more see 4 comments

Know Thy Environment Before Redesigning It

A while ago I had an interesting consulting engagement: a multinational organization wanted to migrate off global Carrier Ethernet VPN (with routers at the edges) to MPLS/VPN.

While that sounds like the right thing to do (after all, L3 must be better than L2, right?) in that particular case they wanted to combine the provider VPN with Internet-based IPsec VPN… and doing that in parallel with MPLS/VPN tends to become an interesting exercise in “how convoluted can I make my design before I give up and migrate to BGP”.

read more see 4 comments

Don't Base Your Design on Vendor Marketing

Remember how Arista promoted VXLAN coupled with deep buffer switches as the perfect DCI solution a few years ago? Someone took Arista’s marketing too literally, ran with the idea and combined VXLAN-based DCI with traditional MLAG+STP data center fabric.

While I love that they wrote a blog post documenting their experience (if only more people would do that), it doesn’t change the fact that the design contains the worst of both worlds.

Here are just a few things that went wrong:

read more see 10 comments

Decide How Badly You Want to Fail

Every time I’m running a data center-related workshop I inevitably get pulled into stretched VLAN and stretched clusters discussion. While I always tell the attendees what the right way of doing this is, and explain the challenges of stretched VLANs from all perspectives (application, database, storage, routing, and broadcast domains) the sad truth is that sometimes there’s nothing you can do.

You’ll find a generic version of that explanation in Building Active-Active and Disaster Recovery Data Centers webinar.

In those sad cases, I can give the workshop attendees only one advice: face the reality, and figure out how badly you might fail. It’s useless pretending that you won’t get into a split-brain scenario - redundant equipment just makes it less likely unless you over-complicated it in which case adding redundancy reduces availability. It’s also useless pretending you won’t be facing a forwarding loop.

read more see 2 comments

Feedback: Data Center Interconnects Webinar

I got great feedback about the first part of Data Center Interconnects webinar from one of ipSpace.net subscribers:

I had no specific expectation when I started watching the material and I must have watched it 6 times by now.

Your webinar covered just the right level of detail to educate myself or refresh my knowledge on the technologies and relevant options for today’s market choices

The information provided is powerful and avoids useless discussions which vendors and PowerPoint pitches. Once you ask the right question it’s easy to get an idea of the vendor readiness

In the first live session we covered the easy cases: design considerations, and layer-3 interconnect with path separation (multiple routing domains). The real fun will start in the second live session on March 19th when we’ll dive into stretched VLANs and long-distance vMotion ideas.

You can attend the live session with any paid ipSpace.net subscriptiondetails here.

add comment
Sidebar