Slow Networking After an Ubuntu Kernel Upgrade
A troubleshooting account of tracing severe network instability after an Ubuntu kernel upgrade to the r8169 driver.
After upgrading Ubuntu 12.04 to kernel 3.13.0-46-generic, web browsing became extremely slow. SSH sessions to other machines dropped immediately, many hosts could not be pinged, and the connection seemed to come and go.
My first suspicion was DNS, but adding 8.8.8.8 did not help. I then tried the universal remedy—a reboot—with no effect. I also suspected the hardware and replaced both the network cable and the network port, but the problem remained. It was clearly local to the computer and was probably caused by software or a driver. Eventually, a Google search led me to the answer.
Cause
The Realtek r8168B network adapter was using the bundled r8169 driver, which dropped a large number of packets on 3.x kernels. Installing the r8168 driver from Realtek resolved the problem.