Blog Posts in January 2013
BGP Security draft adopted as IETF workgroup document
We published the first draft of the BGP Operations and Security document almost a year ago. In the meantime, the authors and Merike Kaeo presented the draft at RIPE and IETF meetings and collected literally tons of feedback (well documented in change logs) ... and finally the draft was adopted as IETF opsec workgroup document and republished under a new name.
We would never get this far without relentless Jerome Durand who did most of the editing heavy lifting, persistent nudging from Gunter Van de Velde and gracious help of Merike Kaeo. Thank you all!
Long-Distance vMotion, Stretched HA Clusters and Business Needs
During a recent vMotion-over-VXLAN discussion Chris Saunders made a very good point: “Folks should be asking a better question, like: Can I use VXLAN and vMotion together to meet my business requirements.”
Yeah, it’s always worth exploring the actual business needs.
Based on a true story ...
A while ago I was sitting in a roomful of extremely intelligent engineers working for a large data center company. Unfortunately they had been listening to a wrong group of virtualization consultants and ended up with the picture-perfect disaster-in-waiting: two data centers bridged together to support a stretched VMware HA cluster.
Free webinar: TCP, HTTP and SPDY
Most web application developers remain blissfully unaware of the major performance roadblocks their applications face in the wild: access network bandwidth restrictions and unexpectedly high latency (see also Fallacies of Distributed Computing with an in-depth explanation). The impact of these two roadblocks is further amplified by behavior of TCP and HTTP, the protocols used by almost all web applications.
These issues are well documented in my Scalable Web Application Design course and in a free TCP, HTTP and SPDY webinar for those of you who won’t be able to make it to Ljubljana.
MTU issues (and TCP MSS clamping) in residential IPv6 deployments
Numerous residential access technologies face path MTU discovery issues. PPPoE connections (with MTU = 1492 bytes instead of 1500 bytes) is the best-known example, and we’ll see more of them as various tunneling-based IPv4-to-IPv6 transition mechanisms (6rd, DS-Lite, MAP-E) become more popular.
Obviously you could use the same old MSS clamping tricks in the brave new IPv6 world or decide (like DS-Lite) to deal with IP fragmentation in underlay access networks ... but there’s another option in the IPv6 world: reduce client-side MTU with router advertisement messages.
NEC Launched a Virtual OpenFlow Switch – Does It Matter?
On January 22nd NEC launched another component of their ProgrammableFlow architecture: a virtual switch for Hyper-V 3.0 environment. The obvious questions to ask would be: (a) why do we care and (b) how’s that different from Nicira or BigSwitch.
TL&DR summary: It depends.
Juniper MX Routers – all you ever wanted to know
During a recent ExpertExpress engagement I got an interesting question: “could we do per-customer policing and shaping on an MX-80 if we want to offer VPLS services and have Q-in-Q encapsulation on customer-facing links?” As I have preciously little Junos/MX knowledge, it was time for the classic “I’ll get back to you” reply and some heavy research.
You probably know how hard it is to find in-depth information on an unknown platform running unfamiliar software. Fortunately, Doug Hanks (@douglashanksjr) sent me a review copy of his new Juniper MX Series book a while ago. It was time for some serious reading.
TCP MSS Clamping – What Is It and Why Do We Need It?
This (not so very) short video explains what TCP MSS clamping is and why we’re almost forced to use it on xDSL (PPPoE) and tunnel interfaces.
TL&DW summary: because Internet-wide Path MTU Discovery rarely works.
DHCPv6-based address allocation on PPPoE links
Cassidy Larson from InfoWest sent me an interesting challenge: using the sample configurations I provided in the Building Large IPv6 Service Provider Networks webinar he was getting weird DHCPv6 errors when a residential CPE device requested a delegated prefix from the BRAS router (before moving forward, have to mention how nice it is to see an US ISP deploying IPv6 ;).
Could you run an MPLS-TE-only MPLS/VPN network without LDP?
One of my readers sent me a surprising question: “We run only LDP in our MPLS network and need to run RSVP for TE and then phase out LDP. How could we do it?”
My first reaction was “Why would you ever want to do that” and I got no reasonable answer (suggestions, anyone?) but let’s focus on “Could you do it?”
TL&DR summary: You could, but that doesn’t mean you should.
How would you like to configure Policy-Based Routing (PBR)
Adam Sweeney, VP of EOS Engineering @ Arista Networks posed me a challenging question after my I-so-hate-PBR-CLI rant: “Is there something in particular that makes the IOS PBR CLI so painful? Is there a PBR CLI provided by any of the other systems out there that you like a lot better?”
My Twitter friends helped me find the answer to the second question: PBR in Junos is even more convoluted than it is in Cisco IOS... but what would be a better CLI?
Redundant Data Center Internet Connectivity – High-Level Design
Yesterday I described the roadblocks you might encounter when faced with a seemingly simple challenge:
In a network with two data centers (connected with a DCI link), ensure the applications in a data center stay reachable even if its Internet links fail.
In the Solutions Corner (a brand new part of my web site) you’ll find a short high-level design document describing the overall solution and listing the technologies you could use to implement it (you might want to watch the video before reading the document).
Redundant Data Center Internet Connectivity – Problem Overview
During one of my ExpertExpress consulting engagements I encountered an interesting challenge:
We have a network with two data centers (connected with a DCI link). How could we ensure the applications in a data center stay reachable even if all local Internet links fail?
On the face of it, the problem seems trivial; after all, you already have the DCI link in place, so what’s the big deal ... but we quickly figured out the problem is trickier than it seems.
When discussing stretched clusters ...
... and someone mentions redundant layer-2 data center interconnect might fail creating a split-brain problem:
Source: DevOps Reactions (HT @Bigmstone)
Edge Protocol Independence: Another Benefit of Edge-and-Core Layering
I asked Martin Casado to check whether I correctly described his HotSDN’12 paper in my Edge and Core OpenFlow post, and he replied with another interesting observation:
The (somewhat nuanced) issue I would raise is that [...] decoupling [also] allows evolving the edge and core separately. Today, changing the edge addressing scheme requires a wholesale upgrade to the core.
The 6PE architecture (IPv6 on the edge, MPLS in the core) is a perfect example of this concept.
Extending MPLS/VPN to Customer Sites
Erich has encountered a familiar MPLS/VPN design challenge:
We have Cisco's 2901s with the data license running MPLS/VPN on customer site (the classical PE is at the customer site). Should we use eBGP between CPE router and network edge router, some sort of iBGP route reflector design, or something completely different?
The “it depends” answer depends primarily on how much you can trust the routers installed at the customer site (CPE routers).
Link Aggregation with Stackable Data Center Top-of-Rack Switches
Tomas Kubica made an interesting comment to my Stackable Data Center Switches blog post: “Suppose all your servers have 4x 10G port and you bundle them to LACP NIC team [...] With this stacking link is not going to be used for your inter-server traffic if all servers have active connections to all nodes of your ToR stack.” While he’s technically correct, the idea of having four 10GE ports on each server just to cater to the whims of stackable switches is somewhat hard to sell.
The Magical U-curve and technology adoption
Simon Gordon introduced me to the magic U-curve during a fantastic meeting with the QFabric team more than a year ago. It turns out you can explain around 80% of IT phenomena with the U-curve (assuming you choose the proper metrics and linear or log scale) … and you can always try the hockey stick if the U-curve fails.
Edge and Core OpenFlow (and why MPLS is not NAT)
More than a year ago, I explained why end-to-end flow-based forwarding doesn’t scale (and Doug Gourlay did the same using way more colorful language) and what the real-life limitations are. Not surprisingly, the gurus that started the whole OpenFlow movement came to the same conclusions and presented them at the HotSDN conference in August 2012 ... but even that hasn’t stopped some people from evangelizing the second coming.