BRAS tuning
===========

Recommendations for BRAS (Broadband Remote Access Server) performance.


Network tuning
--------------

Disable kernel mitigations to maximize performance
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Edit file ``/etc/default/grub``

.. code-block:: sh

  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 

.. code-block:: sh

  $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``:


.. code-block:: sh
  
    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:

.. code-block:: sh


  ethtool -g eth0


Fix Download speed problem (shaper)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Change shaper from htb to tbf

.. code-block:: sh

  [shaper]
  …
  down-limiter=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``

.. code-block:: sh

  [shaper]
  rate-limit=888/888


Change PPPoE MTU
^^^^^^^^^^^^^^^^

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

.. code-block:: sh

  [ppp]
  verbose=1
  min-mtu=1280
  mtu=1492
  mru=1492

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

``nano /lib/udev/ifupdown-hotplug``

.. code-block:: sh

    case "$ACTION" in
    add)
    # these interfaces generate hotplug events *after* they are brought up
    case $INTERFACE in
        ppp*|ippp*|isdn*|plip*|lo|irda*|ipsec*

just add ``|ipoe*`` after ``|ipsec*``

repeat with file ``/lib/udev/net.agent``

SYSTEMD-UDEV optimizations
^^^^^^^^^^^^^^^^^^^^^^^^^^

1. Delete ``99-default.link`` from ``/lib/systemd/network/`` directory

.. code-block:: sh

    rm /lib/systemd/network/99-default.link

2. Change ``/lib/udev/rules.d/99-systemd.rules``

.. code-block:: sh

    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"``

3. Change ``/lib/udev/rules.d/80-ifupdown.rules``

.. code-block:: sh

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

Add ``KERNEL!="ppp*|ipoe*"``