Category: switching

Routed Interfaces on Layer-3 Switches and Internal VLANs

In the Router Interfaces and Switch Ports blog post, I described why we have switch ports and routed interfaces on layer-3 switches. Another blog post in the same series described the conceptual architecture of a layer-3 switch:

  • All interfaces are connected to a VLAN-aware switch
  • The switch interfaces could be access or trunk interfaces1.
  • Each VLAN in a VLAN-aware switch can be connected to an internal router through a VLAN interface.

However, that’s not how we configure layer-3 switches. There’s a significant gap between the conceptual configuration model and the internal architecture:

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The Linux Bridge MTU Hell

It all started with an innocuous article describing the MTU basics. As the real purpose of the MTU is to prevent packet drops due to fixed-size receiver buffers, and I waste spend most of my time in virtual labs, I wanted to check how various virtual network devices react to incoming oversized packets.

As the first step, I created a simple netlab topology in which a single link had a slightly larger than usual MTU… and then all hell broke loose.

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MLAG Deep Dive: LAG Member Failures in VXLAN Fabrics

In the Dealing with LAG Member Failures blog post, we figured out how easy it is to deal with a LAG member failure in a traditional MLAG cluster. The failover could happen in hardware, and even if it’s software-driven, it does not depend on the control plane.

Let’s add a bit of complexity and replace a traditional layer-2 fabric with a VXLAN fabric. The MLAG cluster members still use an MLAG peer link and an anycast VTEP IP address (more details).

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MLAG Deep Dive: Dealing with LAG Member Failures

Craig Weinhold pointed me to a complex topic I managed to ignore in my MLAG Deep Dive series: how does an MLAG cluster reroute around a failure of a LAG member link?

In this blog post, we’ll focus on traditional MLAG cluster implementations using a peer link; another blog post will explore the implications of using VXLAN and EVPN to implement MLAG clusters.

We’ll also ignore the interesting question of “how is the LAG member link failure detected?1 and focus on “what happens next?” using the sample MLAG topology:

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AMS-IX Outage: Layer-2 Strikes Again

On November 22nd, 2023, AMS-IX, one of the largest Internet exchanges in Europe, experienced a significant performance drop lasting more than four hours. While its peak performance is around 10 Tbps, it dropped to about 2.1 Tbps during the outage.

AMS-IX published a very sanitized and diplomatic post-mortem incident summary in which they explained the outage was caused by LACP leakage. That phrase should be a red flag, but let’s dig deeper into the details.

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Path Failure Detection on Multi-Homed Servers

TL&DR: Installing an Ethernet NIC with two uplinks in a server is easy1. Connecting those uplinks to two edge switches is common sense2. Detecting physical link failure is trivial in Gigabit Ethernet world. Deciding between two independent uplinks or a link aggregation group is interesting. Detecting path failure and disabling the useless uplink that causes traffic blackholing is a living hell (more details in this Design Clinic question).

Want to know more? Let’s dive into the gory details.

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Network Security Vulnerabilities: the Root Causes

Sometime last autumn, I was asked to create a short “network security challenges” presentation. Eventually, I turned it into a webinar, resulting in almost four hours of content describing the interesting gotchas I encountered in the past (plus a few recent vulnerabilities like turning WiFi into a thick yellow cable).

Each webinar section started with a short “This is why we have to deal with these stupidities” introduction. You’ll find all of them collected in the Root Causes video starting the Network Security Fallacies part of the How Networks Really Work webinar.

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MLAG Clusters without a Physical Peer Link

With the widespread deployment of Ethernet-over-something technologies, it became possible to build MLAG clusters without a physical peer link, replacing it with a virtual link across the core fabric. Avaya was one of the first vendors to implement virtual peer links with Provider Backbone Bridging (PBB) transport, and some data center switching vendors (example: Cisco) offer similar functionality with VXLAN transport.

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