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+Recommendations
+===============
+
+Enable forwarding
+-----------------
+To enable packet forwarding need edit /etc/sysctl.conf and add or uncomment next:
+
+.. code-block:: sh
+
+  net.ipv4.ip_forward=1
+  net.ipv6.conf.all.forwarding=1
+  
+For apply this params now, use command ``sysctl -p`` or after reboot server this params will be applied automatically.
+
+MTU
+---
+
+If used vlan-per-user often required 802.1ad standard also called as QinQ or Q-in-Q, then need to set MTU on main interface and S-VLAN, because adding to headed one more field.
+Interface which using QinQ usually consist of ``<interface_name>.<S-VLAN>.<C-VLAN>``.
+S-VLAN (Service VLAN) is TAG which wrap C-VLAN (Customer VLAN).
+
+As example: 
+
+.. code-block:: sh
+
+  MTU
+             1504
+               |   1504
+               |   |   1500
+               |   |   |
+            eth0.2001.101
+               |   |   |
+               |   |   C-VLAN
+               |   S-VLAN
+               Interface
+   
+Set up MTU on interface eth0 and interface with S-VLAN
+
+.. code-block:: sh
+
+  ip link set eth0 mtu 1504
+  ip link set eth0.2001 mtu 1504
+
+.. admonition:: Note:
+
+  If used ``bonding`` need change MTU on *bonding* (bond0) and *slaves* (eth0, eth1 ...) interfaces.
+
+Increase ARP cache size
+-----------------------------
+
+If accel-ppp used as DHCP BRAS important to increase ARP cache size, otherwise you can cache overflow and clients have lost connections. Edit /etc/sysctl.conf and add next:
+
+.. code-block:: sh
+
+  net.ipv4.neigh.default.gc_thresh1 = 4096
+  net.ipv4.neigh.default.gc_thresh2 = 8192
+  net.ipv4.neigh.default.gc_thresh3 = 12288
+  net.ipv6.neigh.default.gc_thresh1 = 4096
+  net.ipv6.neigh.default.gc_thresh2 = 8192
+  net.ipv6.neigh.default.gc_thresh3 = 12288
+
+For apply this params now, use command ``sysctl -p`` or after reboot server this params will be applied automatically.