BRAS tuning

Recommendations for BRAS (Broadband Remote Access Server) performance.

Network tuning

Disable kernel mitigations to maximize performance

Edit file /etc/default/grub

GRUB_CMDLINE_LINUX_DEFAULT="intel_idle.max_cstate=0 processor.max_cstate=1 idle=poll quiet mitigations=off"

Additional GRUB CMD arguments:

  • ixgbe.allow_unsupported_sfp=1 - Allow to use not original Intel SFP+ modules

  • pcie_aspm=off - Disable Active-State Power Management

After saving, please update grub settings

$sudo update-grub

Warning! Enabling the idle loop (idle=poll) parameter can cause 100% CPU utilization on your VM (if you’re using virtual enviroments like ProxMox, VMWare, etc.)

Disable NIC offloads

Disable hardware offloads,increase Tx/Rx buffers and queue length on your NICs to prevent speed problems. Please note, that GSO offload changed to tx-gso-partial in Linux kernels 4.15 and later.

Debian /etc/network/interfaces:

allow-hotplug eth0
iface eth0 inet manual
    up ethtool -K eth0 tso off gso off gro off rxvlan off txvlan off rx-vlan-filter off ntuple on &> /dev/null
    up ethtool -K eth0 tx-gso-partial off &> /dev/null
    up ethtool -G eth0 rx 4096 tx 4096 &> /dev/null
    up ip link set eth0 txqueuelen 10000 &> /dev/null

Please determine your NIC queue and buffers limit before increase:

ethtool -g eth0

Fix Download speed problem (shaper)

Change shaper from htb to tbf


Default rate limits (shaper)

If radius-server Access-Accept answer has no compatible speed attributes - to prevent unlimited session speed you can add default rate-limits (in Kbps).

nano /etc/accel-ppp.conf


Change PPPoE MTU

You can adjust allowed PPPoE min/max MTU/MRU settings: nano /etc/accel-ppp.conf


Hotplug optimization

To generate hotplug events on IPoE interfaces (Debian 10):

nano /lib/udev/ifupdown-hotplug

case "$ACTION" in
# these interfaces generate hotplug events *after* they are brought up
case $INTERFACE in

just add |ipoe* after |ipsec*

repeat with file /lib/udev/net.agent

SYSTEMD-UDEV optimizations

  1. Delete from /lib/systemd/network/ directory

rm /lib/systemd/network/
  1. Change /lib/udev/rules.d/99-systemd.rules

ACTION=="add", SUBSYSTEM=="net", KERNEL!="lo|ppp*|ipoe*", RUN+="/lib/systemd/systemd-sysctl --prefix=/net/ipv4/conf/$name --prefix=/net/ipv4/neigh/$name --prefix=/net/ipv6/conf/$name --prefix=/net/ipv6/neigh/$name"

Add |ppp*|ipoe* to KERNEL!="lo"

  1. Change /lib/udev/rules.d/80-ifupdown.rules

SUBSYSTEM=="net", ACTION=="add|remove", KERNEL!="ppp*|ipoe*", RUN+="ifupdown-hotplug"

Add KERNEL!="ppp*|ipoe*"