Mohamed Anwar asked the following question on my post “4 Types of Port Channels and When They're Used".
“I need a clarification, where if a member link fails, what will happen to the traffic already sent over that link ? Is there any mechanism to notify the upper layer about the loss and ask it to resend ? How this link failure will be handled for data traffic and control traffic ?”
— Mohamed Anwar
I think his questions are really important because he hits on two really key aspects of a failure event: what happens in the data plane and what happens in the control plane.
A network designer needs to bear both of these aspects in mind as part of their design. Overlooking either aspect will almost always open the network up to additional risk.
I think it's well understood that port channels add resiliency in the data plane (I cover some of that in the previous article). What may not be well understood is that port channels also contribute to a stable control plane! I'll talk about that below. I'll also address Mohamed's question about what happens to traffic on the failed link.
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Constrained MTU in path between R1 and R4 |
interface Tunnel0
ip address 192.168.1.1 255.255.255.0
no ip redirects
ip mtu 1400
ip pim sparse-mode
ip nhrp map multicast dynamic
ip nhrp network-id 1
tunnel source FastEthernet0/0
tunnel mode gre multipoint
tunnel path-mtu-discovery
tunnel vrf TRANSIT
end
R1#show dmvpn
Legend: Continue reading
ASERT provides a weekly threat bulletin for Arbor customers that highlights and analyzes the week’s top security events and provides other pertinent infosec material. Recently, we covered the public notification of a United Airlines breach by possible Chinese state-sponsored threat actors. In this blog, we offer an alternative hypothesis to the conclusions many have drawn regarding the motivation behind this and other recent attacks.
The Compromises
For those keeping score, the United States Office of Personnel Management (OPM), Anthem, Premera, and Carefirst Blue Cross all reported large data breaches, seemingly perpetrated by the same possible Chinese state-sponsored threat actors [1]. Research into the OPM breach provided information leading investigators to believe the same group of threat actors also compromised additional companies [2]. These investigators released IOC’s that United Airlines used to detect their own data breach in late May/early June of 2015. The data stolen reportedly included passenger manifests containing travel information and basic demographics about travelers. Additionally, according to Bloomberg, one of the individuals familiar with the case indicated information regarding United’s corporate merger and acquisition strategy was also possibly compromised.
Considering the context discussed so far, let’s highlight the current train of thought amongst many in the security Continue reading
This is the text of an internal email I sent at CloudFlare that we thought worth sharing more widely. I annotated it a bit with links that weren't in the original.
"Tim Berners-Lee- Mosaic by Sue Edkins at Sheen Lane Centre" by Robert Smith - Own work. Licensed under CC BY-SA 4.0 via Commons
Subject: Days of future past
Folks,
One of the exciting things about working at CloudFlare is our continual push to stay on top of what's new for our customers. We've pushed things like IPv6 and SPDY in the past; and we'll soon be giving the world DNSSEC and HTTP/2. In the world of SSL we've stayed on top of changes in recommended cipher suites and offer the latest signature algorithms SHA-2 to our customers.
But as we do this we must not forget the old protocols. Because we serve a truly global audience we serve everyone on the planet. It's easy inside a Silicon Valley bubble to think that everyone is on 1Gbps Internet connection with the latest version of Chrome on a new Mac, but the worldwide reality is far different.
We see every type of machine and browser out there. And Continue reading
This is a guest post by Olivier Paugam, SW Architect for the Autodesk Cloud. I really like this post because it shows how bits of infrastructure--Mesos, Kafka, RabbitMQ, Akka, Splunk, Librato, EC2--can be combined together to solve real problems. It's truly amazing how much can get done these days by a small team.
I was tasked a few months ago to come up with a central eventing system, something that would allow our various backends to communicate with each other. We are talking about activity streaming backends, rendering, data translation, BIM, identity, log reporting, analytics, etc. So something really generic with varying load, usage patterns and scaling profile. And oh, also something that our engineering teams could interface with easily. Of course every piece of the system should be able to scale on its own.
I obviously didn't have time to write too much code and picked up Kafka as our storage core as it's stable, widely used and works okay (please note I'm not bound to using it and could switch over to something else). Now I of course could not expose it directly and had to front-end it with some API. Without thinking much I also Continue reading
The latest open source project goes deep into the Linux kernel to improve networking.
Take a network break! In this episode Oracle tells customers to stop security testing on its software, Arista posts a strong Q2, Symantec sells Veritas, F5 releases a new version of Big-IP and more.
The post Network Break 49: Oracle Scolds Customers Over Security appeared first on Packet Pushers.
Furthering the thoughts I’ve put into the forthcoming book on network complexity…
One of the hardest things for designers to wrap their heads around is the concept of unintended consequences. One of the definitional points of complexity in any design is the problem of “push button on right side, weird thing happens over on the left side, and there’s no apparent connection between the two.” This is often just a result of the complexity problem in its base form — the unsolvable triangle (fast/cheap/quality — choose two). The problem is that we often don’t see the third leg of the triangle.
The Liskov substitution principle is one of the mechanisms coders use to manage complexity in object oriented design. The general idea is this: suppose I build an object that describes rectangles. This object can hold the width and the height of the rectangle, and it can return the area of the rectangle. Now, assume I build another object called “square” that overloads the rectangle object, but it forces the width and height to be the same (a square is type of rectangle that has all equal sides, after all). This all seems perfectly normal, right?
Now let’s say Continue reading